Previously we identified the highly conserved amino acids Glu-Leu-Asp-Lys-Trp-Ala (ELDKWA) on the ecto-domain of gp41 as the epitope of a neutralizing monoclonal antibody (2F5) directed against human immunodeficiency virus type 1. In the present study, the sequence defining the epitope was introduced into the loop of antigenic site B of the influenza virus hemagglutinin. The resulting chimeric virus was able to elicit ELDKWA-specific immunoglobulins G and A in antisera of mice. Moreover, the distantly related human immunodeficiency virus type 1 isolates MN, RF, and IIIB were neutralized by these antisera. These data suggest that this conserved B-cell epitope is a promising candidate for inclusion in a vaccine against AIDS. The results also show that influenza virus can be used to effectively present the antigenic structure of this B-cell epitope.

Idiopathic pulmonary alveolar proteinosis (I-PAP) is a rare disease of unknown etiology in which the alveoli fill with lipoproteinaceous material. We report here that I-PAP is an autoimmune disease with neutralizing antibody of immunoglobulin G isotype against granulocyte/macrophage colony-stimulating factor (GM-CSF). The antibody was found to be present in all specimens of bronchoalveolar lavage fluid obtained from 11 I-PAP patients but not in samples from 2 secondary PAP patients, 53 normal subjects, and 14 patients with other lung diseases. It specifically bound GM-CSF and neutralized bioactivity of the cytokine in vitro. The antibody was also found in sera from all I-PAP patients examined but not in sera from a secondary PAP patient or normal subjects, indicating that it exists systemically in I-PAP patients. As lack of GM-CSF signaling causes PAP in congenital cases and PAP-like disease in murine models, our findings strongly suggest that neutralization of GM-CSF bioactivity by the antibody causes dysfunction of alveolar macrophages, which results in reduced surfactant clearance.

B lymphocytes bearing the Leu-1 cell-surface antigen (Leu-1+), the human equivalent of mouse Ly-1+ B lymphocytes, have been detected in human peripheral blood, but there is little information on their frequency and properties. Analysis by fluorescence-activated cell sorter and double immunofluorescence showed that Leu-1+ B cells are consistently present in the peripheral blood and spleens of healthy subjects and constitute 17.0 +/- 5.0% (mean value +/- standard deviation) and 17.3 +/- 3.9%, respectively, of total B cells. When purified Leu-1+ and Leu-1- B lymphocytes were transformed into immunoglobulin-secreting cells by infection with Epstein-Barr virus and the culture fluids were tested for reactivity with self-antigens, at least two important autoantibodies, antibody to the Fc fragment of human immunoglobulin G (rheumatoid factor) and antibody to single-stranded DNA, were found to be made exclusively by Leu-1+ B cells. It is concluded that the Leu-1+ lymphocytes represent a major subset of the normal human B cell repertoire and include the B cells capable of making autoantibodies similar to those found in systemic lupus erythematosus and rheumatoid arthritis.

Sarcoidosis is a polygenic immune disorder with predominant manifestation in the lung. Genome-wide linkage analysis previously indicated that the extended major histocompatibility locus on chromosome 6p was linked to susceptibility to sarcoidosis. Here, we carried out a systematic three-stage SNP scan of 16.4 Mb on chromosome 6p21 in as many as 947 independent cases of familial and sporadic sarcoidosis and found that a 15-kb segment of the gene butyrophilin-like 2 (BTNL2) was associated with the disease. The primary disease-associated variant (rs2076530; P(TDT) = 3 x 10(-6), P(case-control) = 1.1 x 10(-8); replication P(TDT) = 0.0018, P(case-control) = 1.8 x 10(-6)) represents a risk factor that is independent of variation in HLA-DRB1. BTNL2 is a member of the immunoglobulin superfamily and has been implicated as a costimulatory molecule involved in T-cell activation on the basis of its homology to B7-1. The G ->> A transition constituting rs2076530 leads to the use of a cryptic splice site located 4 bp upstream of the affected wild-type donor site. Transcripts of the risk-associated allele have a premature stop in the spliced mRNA. The resulting protein lacks the C-terminal IgC domain and transmembrane helix, thereby disrupting the membrane localization of the protein, as shown in experiments using green fluorescent protein and V5 fusion proteins.

Apical membrane antigen 1 (AMA1), a polymorphic merozoite surface protein, is a leading blood-stage malaria vaccine candidate. A phase 1 trial was conducted with 30 malaria-naive volunteers to assess the safety and immunogenicity of the AMA1-C1 malaria vaccine. AMA1-C1 contains an equal mixture of recombinant proteins based on sequences from the FVO and 3D7 clones of Plasmodium falciparum. The proteins were expressed in Pichia pastoris and adsorbed on Alhydrogel. Ten volunteers in each of three dose groups (5 mug, 20 mug, and 80 mug) were vaccinated in an open-label study at 0, 28, and 180 days. The vaccine was well tolerated, with pain at the injection site being the most commonly observed reaction. Anti-AMA1 immunoglobulin G (IgG) was detected by enzyme-linked immunosorbent assay (ELISA) in 15/28 (54%) volunteers after the second immunization and in 23/25 (92%) after the third immunization, with equal reactivity to both AMA1-FVO and AMA1-3D7 vaccine components. A significant dose-response relationship between antigen dose and antibody response by ELISA was observed, and the antibodies were predominantly of the IgGG purified from sera of vaccinees, demonstrating biological activity of the antibodies. To our knowledge, this is the first AMA1 vaccine candidate to elicit functional immune responses in malaria-naive humans, and our results support the further development of this vaccine.

Antiviral antibody production is often sustained for long periods after resolution of an acute viral infection. Despite extensive documentation of this phenomenon, the mechanisms involved in maintaining long-term antibody production remain poorly defined. As a first step towards understanding the nature of long-term humoral immunity, we examined the anatomical location of antibody-producing cells during acute viral infection. Using the lymphocytic choriomeningitis virus (LCMV) model, we found that after resolution of the acute infection, when antiviral plasma cells in the spleen decline, a population of virus-specific plasma cells appears in the bone marrow and constitutes the major source of long-term antibody production. Following infection of adult mice, LCMV-specific antibody-secreting cells (ASC) peaked in the spleen at 8 days postinfection but were undetectable in the bone marrow at that time. The infection was essentially cleared by 15 days, and the ASC numbers in the spleen rapidly declined while an increasing population of LCMV-specific ASC began to appear in the bone marrow. Compared with the peak response at 8 days postinfection, time points from 30 days to more than 1 year later demonstrated greater-than-10-fold reductions in splenic ASC. In contrast, LCMV-specific plasma cell numbers in the bone marrow remained high and correlated with the high levels of antiviral serum antibody. The presence of LCMV-specific plasma cells in the bone marrow was not due to persistent infection at this site, since the virus was cleared from both the spleen and bone marrow with similar kinetics as determined by infectivity and PCR assays. The immunoglobulin G subclass profile of antibody-secreting cells derived from bone marrow and the spleen correlated with the immunoglobulin G subclass distribution of LCMV-specific antibody in the serum. Upon rechallenge with LCMV, the spleen exhibited a substantial increase in virus-specific plasma cell numbers during the early phase of the secondary response, followed by an equally sharp decline. Bone marrow ASC populations and LCMV-specific antibody levels in the serum did not change during the early phase of the reinfection, but both increased about two-fold by 15 days postchallenge. After both primary and secondary viral infections, LCMV-specific plasma cells were maintained in the bone marrow, showing that the bone marrow is a major site of long-term antibody production after acute viral infection. These results documenting long-term persistence of plasma cells in the bone marrow suggest a reexamination of our current notions regarding the half-life of plasma cells.

Minor histocompatibility antigens (mHAs) are known targets of donor T cells after allogeneic hematopoietic stem cell transplantation (HSCT). In contrast, B-cell responses to mHAs have not been extensively characterized and the clinical significance of antibodies to mHAs is unknown. We tested 121 patients who underwent HSCT and 134 healthy donors for immunoglobulin G (IgG) antibodies against 5 mHAs encoded by genes on the Y chromosome (DBY, UTY, ZFY, RPS4Y, and EIF1AY). Antibodies to at least one H-Y protein developed in 52% of male patients with female donors compared with 8.7% of male patients with male donors (P < .0001), and in 41.4% of healthy females compared with 7.8% of healthy males (P < .0001). H-Y antibodies develop 4 to 12 months after transplantation and persist for long periods. The clinical significance of H-Y antibodies was characterized in 75 male patients with hematologic malignancies who received stem cells from female donors (F ->> M HSCT). The presence of H-Y antibodies correlated with chronic graft-versus-host disease (GVHD) by univariate (odds ratio [OR] = 15.5; P < .0001) and multivariable logistic regression analysis (OR = 56.5; P < .0001). Antibody response to Y-chromosome encoded histocompatibility antigens (H-Y antigens) was also associated with maintenance of disease remission (P < .0001). B cells may provide a new target for immune intervention in chronic GVHD.

The known T-cell receptors (TCRs) involved in the recognition of antigen and major histocompatibility complex (MHC) molecules are glycoproteins comprised of polymorphic disulphide-linked alpha- and beta-chains. The genes encoding these chains are homologous to immunoglobulin genes and consist of V (variable), J (joining) and C (constant) regions that rearrange during development. TCRs are expressed relatively late in thymocyte development and only in association with an invariant molecular complex of proteins termed T3. Immature thymocytes do not express the TCR-T3 complex but do express messenger RNA encoding a third rearranging T-cell receptor-like gene, termed T gamma. Here we report a clone of normal immature T4-T8- human thymocytes, designated CII, which does not express mature mRNA for T alpha or T beta genes, but does express high levels of T gamma mRNA. This clone also expresses high levels of surface T3, and antibodies to T3 induce immunologically relevant functions in CII cells. Immunoprecipitation of CII surface-labelled proteins with anti-T3 co-precipitates a T3 molecular complex together with two additional and novel peptides of relative molecular mass (Mr), 44,000 (44K) and 62,000 (62K).

The most common translocation in human lymphoma, the t(14;18)(q32;q21), generates heterogeneous 4.2-7.2 kb Bcl-2-immunoglobulin (Ig) chimeric mRNAs resulting from alternative Bcl-2 5' exons and varied Ig 3' untranslated regions (UT). The normal human Bcl-2 gene has a three exon structure with an untranslated first exon, a facultative 220 bp intron I, but an enormous 370 kb intron II. S1 protection and primer extension analysis defined initiation sites in exon II associated with classic promoter elements and a decanucleotide (ATG-CAAAGCA) homologous with Ig variable region enhancers. Multiple initiation sites were also found in a GC-rich region with Sp1 binding motifs in exon I. Most t(14;18) breakpoints cluster within the 3' UT of Bcl-2 implicating that event in gene deregulation. The Bcl-2 gene introduced into the Ig constant (C gamma) locus of SU-DHL-6 displayed somatic mutation. While Bcl-2--Ig mRNAs demonstrated an unaltered 2.5 h half-life, the Bcl-2--Ig gene revealed an inappropriately high rate of transcription for a mature B-cell. This indicates the translocated Bcl-2 allele has escaped normal control mechanisms.

It is not understood how immune inflammation influences the pathogenesis of severe acute respiratory syndrome (SARS). One area of strong controversy is the role of interferon (IFN) responses in the natural history of SARS. The fact that the majority of SARS patients recover after relatively moderate illness suggests that the prevailing notion of deficient type I IFN-mediated immunity, with hypercytokinemia driving a poor clinical course, is oversimplified. We used proteomic and genomic technology to systematically analyze host innate and adaptive immune responses of 40 clinically well-described patients with SARS during discrete phases of illness from the onset of symptoms to discharge or a fatal outcome. A novel signature of high IFN-alpha, IFN-gamma, and IFN-stimulated chemokine levels, plus robust antiviral IFN-stimulated gene (ISG) expression, accompanied early SARS sequelae. As acute illness progressed, SARS patients entered a crisis phase linked to oxygen saturation profiles. The majority of SARS patients resolved IFN responses at crisis and expressed adaptive immune genes. In contrast, patients with poor outcomes showed deviated ISG and immunoglobulin gene expression levels, persistent chemokine levels, and deficient anti-SARS spike antibody production. We contend that unregulated IFN responses during acute-phase SARS may culminate in a malfunction of the switch from innate immunity to adaptive immunity. The potential for the use of the gene signatures we describe in this study to better assess the immunopathology and clinical management of severe viral infections, such as SARS and avian influenza (H5N1), is therefore worth careful examination.

1,25-Dihydroxyvitamin D3 [1,25-(OH)2-D3] is known to be an immunosuppressive hormone. This review primarily deals with in vitro and in vivo effects of 1,25-(OH)2-D3 and analogue, 1,25-dihydroxy-16ene-vitamin D3 [1,25-(OH)2-16ene-D3], on T helper subsets type 1 (Th1) or type 2 (Th2) that have distinctive functional characteristics in humans. Th1 secrete interferon (IFN-gamma), interleukin (IL-2) and induce B cells to produce immunoglobulin IgG2a while Th2 secrete IL-4, IL-10 and induce the production of IgG1 and IgE by B cells. The sterol inhibits the secretion of IL-12, a cytokine produced by monocytes and B cells, which leads to the activation and differentiation of Th1. In addition, 1,25-(OH)2-D3 directly inhibits IFN-gamma secretion by Th1 clones while it has little effect on IL-4 secretion by Th2 clones. The analogue, 1,25-(OH)2-16ene-D3, is 100-fold more potent than 1,25-(OH)2-D3 in inhibiting IFN-gamma secretion but also has little effect on IL-4 secretion. In mice, when given in vivo, the sterol prevents the induction of spontaneous and induced autoimmune diseases and inhibits Th1 induce IgG2a responses. These actions of the vitamin D3 compounds suggest that it may have potential therapeutic applications in Th1-mediated clinical situations such as autoimmunity and transplantation.

OBJECTIVE

To investigate in the prospective Helsinki Heart Study, whether chronic Chlamydia pneumoniae infection, indicated by elevated antibody titers against the pathogen, chlamydial lipopolysaccharide-containing immune complexes, or both, is a risk factor for coronary heart disease.

METHODS

The Helsinki Heart Study was a randomized, double-blind, 5-year clinical trial to test the efficacy of gemfibrozil in reducing the risk for coronary heart disease. Participants were randomized to receive either gemfibrozil (2046 patients) or placebo (2035 patients). Fatal and nonfatal myocardial infarction and sudden cardiac death were the main study end points. Serum samples were collected at 3-month intervals from all patients.

METHODS

One hundred forty cardiac events occurred during the follow-up period. Serum samples from 103 case patients obtained 3 to 6 months before a cardiac end point were matched with those from controls for time point, locality, and treatment. Samples were tested for markers of chronic chlamydial infection.

METHODS

Immunoglobulin A (IgA) and G (IgG) antibodies to C. pneumoniae were measured using the microimmunofluorescence method. Lipopolysaccharide-containing immune complexes were measured using two antigen-specific enzyme immunoassays, the lipopolysaccharide-capture and immunoglobulin M (IgM)-capture methods.

RESULTS

Using a conditional logistic regression model, odds ratios for the development of coronary heart disease were 2.7 (95% CI, 1.1 to 6.5) for elevated IgA titers, 2.1 (CI, 1.1 to 3.9) for the presence of immune complexes, and 2.9 (CI, 1.5 to 5.4) for the presence of both factors. If we adjusted for other coronary heart disease risk factors such as age, hypertension, and smoking, the corresponding values would be 2.3 (CI, 0.9 to 6.2), 1.8 (CI, 0.9 to 3.6), and 2.6 (CI, 1.3 to 5.2), respectively.

CONCLUSIONS

The results suggest that chronic C. pneumoniae infection may be a significant risk factor for the development of coronary heart disease.

The immunoglobulin light-chain gene enhancers E kappa 3', E lambda 2-4, and E lambda 3-1 contain a conserved cell type-specific composite element essential for their activities. This element binds a B cell-specific heterodimeric protein complex that consists of the Ets family member PU.1 and a second factor (NF-EM5), whose participation in the formation of the complex is dependent on the presence of DNA-bound PU.1. In this report we describe the cloning and characterization of Pip (PU.1 interaction partner), a lymphoid-specific protein that is most likely NF-EM5. As expected, the Pip protein binds the composite element only in the presence of PU.1; furthermore, the formation of this ternary complex is critically dependent on phosphorylation of PU.1 at serine-148. The Pip gene is expressed specifically in lymphoid tissues in both B- and T-cell lines. When coexpressed in NIH-3T3 cells, Pip and PU.1 function as mutually dependent transcription activators of the composite element. The amino-terminal DNA-binding domain of Pip exhibits a high degree of homology to the DNA-binding domains of members of the interferon regulatory factor (IRF) family, which includes IRF-1, IRF-2, ICSBP, and ISGF3 gamma.

A B cell lymphoma-associated chromosomal translocation, t(10;14)(q24;q32), juxtaposes the immunoglobulin C alpha 1 locus to a novel gene, lyt-10. The normal lyt-10 cDNA codes for a 98 kd protein which displays amino-terminal homology with the rel (DNA-binding) domain of the NF-kappa B-rel family of transcription factors and carboxy-terminal homology with the NF-kappa B p50 precursor protein, including the putative proteolytic cleavage domain (poly-G) and the ankyrin-like repeat domains. The lyt-10 protein can bind to kappa B sequences in vitro, although with different specificity from NF-kappa B p50, and in vitro DNA-binding is activated by removal of the ankyrin domain. Chromosomal translocation generates an lyt-10-C alpha 1 fusion gene coding for a protein that retains the rel effector domain, lacks the ankyrin regulatory domain, and binds kappa B sequences in vitro, suggesting its constitutive activation in vivo. Analogous rearrangements of the lyt-10 gene have been found in an additional three cases of lymphoid neoplasia. The lyt-10 gene defines a new subfamily (rel/poly-G/ankyrin) of NF-kappa B-rel transcription factors with potential for oncogenic activation in human cancer.

Infrared spectra have been obtained for 12 globular proteins in aqueous solution at 20 degrees C. The proteins studied, which vary widely in the relative amounts of different secondary structures present, include myoglobin, hemoglobin, immunoglobulin G, concanavalin A, lysozyme, cytochrome c, alpha-chymotrypsin, trypsin, ribonuclease A, alcohol dehydrogenase, beta 2-microglobulin, and human class I major histocompatibility complex antigen A2. Criteria for evaluating how successfully the spectra due to liquid and gaseous water are subtracted from the observed spectrum in the amide I region were developed. Comparisons of second-derivative amide I spectra with available crystal structure data provide both qualitative and quantitative support for assignments of infrared bands to secondary structures. Band frequency assignments assigned to alpha-helix, beta-sheet, unordered, and turn structures are highly consistent among all proteins and agree closely with predictions from theory. alpha-Helix and unordered structures can each be assigned to only one band whereas multiple bands are associated with beta-sheets and turns. These findings demonstrate a method of analysis of second-derivative amide I spectra whereby the frequencies of bands due to different secondary structures can be obtained. Furthermore, the band intensities obtained provide a useful method for estimating the relative amounts of different structures.

OBJECTIVE

Human immunodeficiency virus (HIV)-1 infection has been associated with enhanced microbial translocation, and microbial translocation is a mechanism through which alcohol and some enteric conditions cause liver disease. We hypothesized that HIV promotes liver disease by enhancing microbial translocation.

METHODS

We studied human cohorts in which hepatitis C virus (HCV) and HIV outcomes were carefully characterized.

RESULTS

HIV-related CD4(+) lymphocyte depletion was strongly associated with microbial translocation as indicated by elevated levels of circulating lipopolysaccharide (LPS), LPS-binding protein, soluble CD14, and fucose-binding lectin (AAL) reactive to immunoglobulin G specific for the alpha-galactose epitope and suppressed levels of endotoxin core antibodies (EndoCAb IgM) in HIV-infected subjects compared with the same persons before they had HIV infection and compared with HIV-uninfected subjects. The same measures of microbial translocation were strongly associated with HCV-related liver disease progression (cirrhosis), eg, LPS, odds ratio, 19.0 (P = .002); AAL, odds ratio, 27.8 (P < .0001); in addition, levels of LPS were elevated prior to recognition of cirrhosis.

CONCLUSIONS

Microbial translocation may be a fundamental mechanism through which HIV accelerates progression of chronic liver disease.

Occupancy of the T-cell receptor complex does not appear to be a sufficient stimulus to induce a T-cell-mediated immune response. Increasing evidence suggests that cognate cell-cell interaction between an activated T cell and an antigen-presenting cell may provide such a stimulus. A candidate T-cell surface molecule for this costimulatory signal is the T-cell-restricted CD28 antigen. Following crosslinking with anti-CD28 mAb, suboptimally stimulated CD28+ T cells show increased proliferation and markedly increased secretion of a subset of lymphokines. Recently, the B-cell surface activation antigen B7 was shown to be a natural ligand for the CD28 molecule, and both B7 and CD28 are members of the immunoglobulin superfamily. Here we report that B7-transfected CHO cells can induce suboptimally activated CD28+ T cells to proliferate and secrete high levels of interleukin 2. The response is identical whether T cells are submitogenically stimulated with either phorbol myristate acetate or anti-CD3 to activate the T cells. This response is specific and can be totally abrogated with anti-B7 monoclonal antibody. As has previously been observed for anti-CD28 monoclonal antibody, B7 ligation induced secretion of interleukin 2 but not interleukin 4. We have previously demonstrated that B7 expression is restricted to activated B lymphocytes and interferon gamma-activated monocytes. Since these two cellular populations are involved in antigen presentation as well as cognate interaction with T lymphocytes, B7 is likely to represent a central constimulatory signal that is capable of amplifying an immune response.

Recurrent outbreaks of highly pathogenic avian influenza virus pose the threat of pandemic spread of lethal disease and make it a priority to develop safe and effective vaccines. Influenza virus-like particles (VLPs) have been suggested to be a promising vaccine approach. However, VLP-induced immune responses, and their roles in inducing memory immune responses and cross-protective immunity have not been investigated. In this study, we developed VLPs containing influenza virus A/PR8/34 (H1N1) hemagglutinin (HA) and matrix (M1) proteins and investigated their immunogenicity, long-term cross-protective efficacy, and effects on lung proinflammatory cytokines in mice. Intranasal immunization with VLPs containing HA induced high serum and mucosal antibody titers and neutralizing activity against PR8 and A/WSN/33 (H1N1) viruses. Mice immunized with VLPs containing HA showed little or no proinflammatory lung cytokines and were protected from a lethal challenge with mouse-adapted PR8 or WSN viruses even 5 months postimmunization. Influenza VLPs induced mucosal immunoglobulin G and cellular immune responses, which were reactivated rapidly upon virus challenge. Long-lived antibody-secreting cells were detected in the bone marrow of immunized mice. Immune sera administered intranasally were able to confer 100% protection from a lethal challenge with PR8 or WSN, which provides further evidence that anti-HA antibodies are primarily responsible for preventing infection. Taken together, these results indicate that nonreplicating influenza VLPs represent a promising strategy for the development of a safe and effective vaccine to control the spread of lethal influenza viruses.

In the mid-1980s, Mosmann, Coffman, and their colleagues discovered that murine CD4+ helper T-cell clones could be distinguished by the cytokines they synthesized. The isolation of human Th1 and Th2 clones by Romagnani and coworkers in the early 1990s has led to a large number of reports on the effects of Th1 and Th2 on the human immune system. More recently, cells other than CD4+ T cells, including CD8+ T cells, monocytes, NK cells, B cells, eosinophils, mast cells, basophils, and other cells, have been shown to be capable of producing "Th1" and "Th2" cytokines. In this review, we examine the literature on human diseases, using the nomenclature of type 1 (Th1-like) and type 2 (Th2-like) cytokines, which includes all cell types producing these cytokines rather than only CD4+ T cells. Type 1 cytokines include interleukin-2 (IL-2), gamma interferon, IL-12 and tumor necrosis factor beta, while type 2 cytokines include IL-4, IL-5, IL-6, IL-10, and IL-13. In general, type 1 cytokines favor the development of a strong cellular immune response whereas type 2 cytokines favor a strong humoral immune response. Some of these type 1 and type 2 cytokines are cross-regulatory. For example, gamma interferon and IL-12 decrease the levels of type 2 cytokines whereas IL-4 and IL-10 decrease the levels of type 1 cytokines. We use this cytokine perspective to examine human diseases including infections due to viruses, bacteria, parasites, and fungi, as well as selected neoplastic, atopic, rheumatologic, autoimmune, and idiopathic-inflammatory conditions. Clinically, type 1 cytokine-predominant responses should be suspected in any delayed-type hypersensitivity-like granulomatous reactions and in infections with intracellular pathogens, whereas conditions involving hypergammaglobulinemia, increased immunoglobulin E levels, and/or eosinophilia are suggestive of type 2 cytokine-predominant conditions. If this immunologic concept is relevant to human diseases, the potential exists for novel cytokine-based therapies and novel cytokine-directed preventive vaccines for such diseases.

The Streptococcus pneumoniae capsule is vital for virulence and may inhibit complement activity and phagocytosis. However, there are only limited data on the mechanisms by which the capsule affects complement and the consequences for S. pneumoniae interactions with phagocytes. Using unencapsulated serotype 2 and 4 S. pneumoniae mutants, we have confirmed that the capsule has several effects on complement activity. The capsule impaired bacterial opsonization with C3b/iC3b by both the alternative and classical complement pathways and also inhibited conversion of C3b bound to the bacterial surface to iC3b. There was increased binding of the classical pathway mediators immunoglobulin G (IgG) and C-reactive protein (CRP) to unencapsulated S. pneumoniae, indicating that the capsule could inhibit classical pathway complement activity by masking antibody recognition of subcapsular antigens, as well as by inhibiting CRP binding. Cleavage of serum IgG by the enzyme IdeS reduced C3b/iC3b deposition on all of the strains, but there were still marked increases in C3b/iC3b deposition on unencapsulated TIGR4 and D39 strains compared to encapsulated strains, suggesting that the capsule inhibits both IgG-mediated and IgG-independent complement activity against S. pneumoniae. Unencapsulated strains were more susceptible to neutrophil phagocytosis after incubation in normal serum, normal serum treated with IdeS, complement-deficient serum, and complement-deficient serum treated with IdeS or in buffer alone, suggesting that the capsule inhibits phagocytosis mediated by Fcgamma receptors, complement receptors, and nonopsonic receptors. Overall, these data show that the S. pneumoniae capsule affects multiple aspects of complement- and neutrophil-mediated immunity, resulting in a profound inhibition of opsonophagocytosis.

The neonatal Fc receptor (FcRn) transports immunoglobulin G (IgG) across epithelia, binding IgG in acidic vesicles (pH < or = 6.5) and releasing IgG in the blood at pH 7.4. Well-ordered FcRn/Fc crystals are prevented by the formation of "oligomeric ribbons" of FcRn dimers bridged by Fc homodimers, thus we crystallized a 1:1 complex between rat FcRn and a heterodimeric Fc containing only one FcRn binding site. The 2.8 A complex structure demonstrates that FcRn uses its alpha2 and beta2-microglobulin domains and carbohydrate to interact with the Fc C(gamma)2-C(gamma)3 interface. The structure reveals conformational changes in Fc and three titratable salt bridges that confer pH-dependent binding, and can be used to guide rational design of therapeutic IgGs with longer serum half-lives.

Cosmid clones containing the human gamma, epsilon and alpha heavy chain constant region genes and an epsilon pseudogene have been isolated. All these genes have a switch sequence detectable by hybridization. We have studied overlapping cosmids covering two separate regions of the genome, and the gene order in each of these regions was found to be gamma-gamma-epsilon-alpha. This implies an evolutionary duplication in this multigene family involving gamma, epsilon and alpha genes.

In both immunoglobulins (Ig) and T cell receptors (TCR), the rearrangement of V, D, and J region sequence elements during lymphocyte maturation creates an enormous degree of diversity in an area referred to as the complementarity determining region 3 (CDR3) loop. Variations in the particular V, D, and J elements used, precise points of recombination, and random nucleotide addition all lead to extensive length and sequence heterogeneity. CDR3 loops are often critical for antigen binding in Igs and appear to provide the principal peptide binding residues in TCRs. To better understand the physical and selective constraints on these sequences, we have compiled information on CDR3 size variation for Ig H, L (kappa and lambda) and TCR alpha, beta, gamma, and delta. Ig H and TCR delta CDR3s are the most variable in size and are significantly longer than L and gamma chains, respectively. In contrast, TCR alpha and beta chain distributions are highly constrained, with nearly identical average CDR3 lengths, and their length distributions are not altered by thymic selection. Perhaps most significantly, these CDR3 length profiles suggest that gamma/delta TCRs are more similar to Igs than to alpha/beta TCRs in their putative ligand binding region, and thus gamma/delta and alpha/beta T cells may have fundamentally different recognition properties.

Human T cells that express a T cell antigen receptor (TCR) containing <em>γ</em>-chain variable region 9 and δ-chain variable region 2 (V<em>γ</em>9Vδ2) recognize phosphorylated prenyl metabolites as antigens in the presence of antigen-presenting cells but independently of major histocompatibility complex (MHC), the MHC class I-related molecule MR1 and antigen-presenting CD1 molecules. Here we used genetic approaches to identify the molecule that binds and presents phosphorylated antigens. We found that the butyrophilin BTN3A1 bound phosphorylated antigens with low affinity, at a stoichiometry of 1:1, and stimulated mouse T cells with transgenic expression of a human V<em>γ</em>9Vδ2 TCR. The structures of the BTN3A1 distal domain in complex with host- or microbe-derived phosphorylated antigens had an <em>immunoglobulin</em>-like fold in which the antigens bound in a shallow pocket. Soluble V<em>γ</em>9Vδ2 TCR interacted specifically with BTN3A1-antigen complexes. Accordingly, BTN3A1 represents an antigen-presenting molecule required for the activation of V<em>γ</em>9Vδ2 T cells.