During apoptotic cell death, cell surface ligands initiate phagocytosis of the dying cell. Clearance of these apoptotic cells is thought to occur without an immune response. Since a number of autoantigens are located at the cell surface or within apoptotic blebs, we examined whether exposure of mice to syngeneic apoptotic cells by the intravenous route could induce autoantibody production. Normal mice injected with syngeneic apoptotic thymocytes developed antinuclear autoantibodies and anticardiolipin and anti-ssDNA antibodies. The autoantibody levels were generally lower than those observed in MRL/Faslpr mice and were transient. Surprisingly, six out of six immunized mice demonstrated immunoglobulin G deposition in the glomeruli several months after immunization. These findings indicate that systemic exposure to apoptotic cells can induce an immune response in normal mice, and may help to explain antigen selection and initiation of the immune response in diseases characterized by increased rates of apoptosis such as AIDS and, possibly, systemic lupus erythematosus.

The development and maturation of the immune system in zebrafish was investigated using immune-related gene expression profiling by quantitative real-time polymerase chain reaction, in situ hybridization (ISH), immunoglobulin (Ig) detection by immuno-affinity purification and Western blotting as well as immersion immunization experiments. Ikaros expression was first detected at 1 day post-fertilization (dpf) and thereafter increased gradually to more than two-fold between 28 and 42dpf before decreasing to less than the initial 1dpf expression level in adult fish (aged 105dpf). Recombination activating gene-1 (Rag-1) expression levels increased rapidly (by 10-fold) between 3 and 17dpf, reaching a maximum between 21 and 28dpf before decreasing gradually. However, in adult fish aged 105dpf, the expression level of Rag-1 had dropped markedly, and was equivalent to the expression level at 3dpf. T-cell receptor alpha constant region and immunoglobulin light chain constant region (IgLC) isotype-1, 2 and 3 mRNAs were detected at low levels by 3dpf and their expression levels increased steadily to the adult range between 4 and 6 weeks post-fertilization (wpf). Using tissue-section ISH, Rag-1 expression was detected in head kidney by 2wpf while IgLC-1, 2 and 3 were detected in the head kidney and the thymus by 3wpf onwards. Secreted Ig was only detectable using immuno-affinity purification and Western blotting by 4wpf. Humoral response to T-independent antigen (formalin-killed Aeromonas hydrophila) and T-dependent antigen (human gamma globulin) was observed in zebrafish immunized at 4 and 6wpf, respectively, indicating that immunocompetence was achieved. The findings reveal that the zebrafish immune system is morphologically and functionally mature by 4-6wpf.

BACKGROUND

The source and route of autochthonous hepatitis E virus (HEV) infections are not clearly established in industrialized countries despite evidence that it is a zoonosis in pigs. We investigated the role of figatellu, a traditional pig liver sausage widely eaten in France and commonly consumed raw, as a source of HEV infection.

METHODS

A case-control study was conducted of 3 patients who presented autochthonous hepatitis E and 15 members of their 3 different families. Anti-HEV immunoglobulin G and immunoglobulin M antibody testing was performed with commercial assays. HEV RNA was detected in serum samples of patients and in pig liver sausages by means of real-time polymerase chain reaction and sequenced by means of in-house sequencing assays. Genetic links between HEV sequences were analyzed.

RESULTS

Acute or recent HEV infection, defined by detection of anti-HEV immunoglobulin M antibodies and/or HEV RNA, was observed in 7 of 13 individuals who ate raw figatellu and 0 of 5 individuals who did not eat raw figatellu (P=.041). Moreover, HEV RNA of genotype 3 was recovered from 7 of 12 figatelli purchased in supermarkets, and statistically significant genetic links were found between these sequences and those recovered from patients who ate raw figatellu.

CONCLUSIONS

Our findings strongly support the hypothesis of HEV infection through ingestion of raw figatellu.

Human monocytes contain two distinct receptor sites, one specific for the third component of complement (C'3), the other for immunoglobulin G(gammaG). The two receptors may function either independently or cooperatively in the induction of phagocytosis. Ingestion of erythrocytes coated with immunoglobulin M antibody requires a relatively large number of bound C'3 molecules per cell. Ingestion of erythrocytes sensitized with gammaG antibody is independent of complement; however, the reaction is inhibited by concentrations of gammaG far below those in normal serum. Inhibition by gammaG-globulin is overcome by a relatively small number of bound C'3 molecules per cell. The two monocyte receptors exert a cooperative effect on ingestion by monocytes of erythrocytes coated with gammaG antibody in the presence of inhibitory amounts of free gammaG.

OBJECTIVE

Steroid-refractory Crohn's disease responds to therapy with the chimeric anti-tumor necrosis factor (TNF)-alpha antibody infliximab. Etanercept, a recombinant TNF receptor/immunoglobulin G fusion protein, is highly effective in rheumatoid arthritis but not in Crohn's disease. Because both infliximab and etanercept are TNF-alpha-neutralizing drugs, we investigated the differences in TNF-alpha-neutralizing capacity and human lymphocyte binding and apoptosis-inducing capacity of both molecules.

METHODS

We used a nuclear factor kappaB reporter assay and a cytotoxicity bioassay to study TNF-alpha neutralization by infliximab and etanercept. Lymphocyte binding and apoptosis-inducing capacity was investigated using fluorescence-activated cell sorter analysis, annexin V staining, and cleaved caspase-3 immunoblotting using mixed lymphocyte reaction-stimulated peripheral blood lymphocytes (PBL) from healthy volunteers and lamina propria T cells from patients with Crohn's disease.

RESULTS

Both infliximab and etanercept neutralized TNF-alpha effectively. Infliximab bound to activated PBL and lamina propria T cells, whereas binding of etanercept was equal to a nonspecific control antibody. Infliximab but not etanercept induced peripheral and lamina propria lymphocyte apoptosis when compared with a control antibody. Infliximab activated caspase 3 in a time-dependent manner, whereas etanercept did not.

CONCLUSIONS

Although both infliximab and etanercept showed powerful TNF-alpha neutralization, only infliximab was able to bind to PBL and lamina propria T cells and subsequently to induce apoptosis of activated lymphocytes. These data may provide a biological basis for the difference in efficacy of the 2 TNF-alpha-neutralizing drugs.

Hepatitis E virus (HEV) is endemic in many developing and some industrialized countries. It has been hypothesized that animals may be the source of infection. The recent identification of swine HEV in U.S. pigs and the demonstration of its ability to infect across species have lent credence to this hypothesis. To assess the potential risk of zoonotic HEV infection, we tested a total of 468 veterinarians working with swine (including 389 U.S. swine veterinarians) and 400 normal U.S. blood donors for immunoglobulin G anti-HEV. Recombinant capsid antigens from a U.S. strain of swine HEV and from a human HEV strain (Sar-55) were each used in an enzyme-linked immunosorbent assay. The anti-HEV prevalence assayed with the swine HEV antigen showed 97% concordance with that obtained with the human HEV antigen (kappa = 92%). Among the 295 swine veterinarians tested from the eight U.S. states (Minnesota, Indiana, Nebraska, Iowa, Illinois, Missouri, North Carolina, and Alabama) from which normal blood donor samples were available, 26% were positive with Sar-55 antigen and 23% were positive with swine HEV antigen. In contrast, 18% of the blood donors from the same eight U.S. states were positive with Sar-55 antigen and 17% were positive with swine HEV antigen. Swine veterinarians in the eight states were 1.51 times more likely when tested with swine HEV antigen (95% confidence interval, 1.03 to 2.20) and 1.46 times more likely when tested with Sar-55 antigen (95% confidence interval, 0.99 to 2.17) to be anti-HEV positive than normal blood donors. We did not find a difference in anti-HEV prevalence between veterinarians who reported having had a needle stick or cut and those who had not or between those who spent more time >> or = 80% of the time) and those who spent less time (< or = 20% of the time) working with pigs. Similarly, we did not find a difference in anti-HEV prevalence according to four job categories (academic, practicing, student, and industry veterinarians). There was a difference in anti-HEV prevalence in both swine veterinarians and blood donors among the eight selected states, with subjects from Minnesota six times more likely to be anti-HEV positive than those from Alabama. Age was not a factor in the observed differences from state to state. Anti-HEV prevalence in swine veterinarians and normal blood donors was age specific and paralleled increasing age. The results suggest that swine veterinarians may be at somewhat higher risk of HEV infection than are normal blood donors.

T follicular helper (Tfh) cells help development of antibody responses via interleukin-21 (IL-21). Here we show that activated human dendritic cells (DCs) induced naive CD4(+) T cells to become IL-21-producing Tfh-like cells through IL-12. CD4(+) T cells primed with IL-12 induced B cells to produce immunoglobulins in a fashion dependent on IL-21 and inducible costimulator (ICOS), thus sharing fundamental characteristics with Tfh cells. The induction of Tfh-like cells by activated DCs was inhibited by neutralizing IL-12. IL-12 induced two different IL-21-producers: IL-21(+)IFN-gamma(+)T-bet(+) Th1 cells and IL-21(+)IFN-gamma(-)T-bet(-) non-Th1 cells, in a manner dependent on signal transducer and activator of transcription 4 (STAT4). IL-12 also regulated IL-21 secretion by memory CD4(+) T cells. Thus, IL-12 produced by activated DCs regulates antibody responses via developing IL-21-producing Tfh-like cells and inducing IL-21 secretion from memory CD4(+) T cells. These data suggest that the developmental pathway of Tfh cells differs between mice and humans, which have considerable implications for vaccine development.

C.B-17 severe combined immunodeficient (scid) mice carry the scid mutation and are severely deficient in both T cell- and B cell-mediated immunity, apparently as a result of defective V(D)J joining of the immunoglobulin and T-cell receptor gene elements. In the present studies, we have defined the tissue, cellular, and molecular basis of another characteristic of these mice: their hypersensitivity to ionizing radiation. Bone marrow stem cells, intestinal crypt cells, and epithelial skin cells from scid mice are 2- to 3-fold more sensitive when irradiated in situ than are congenic BALB/c or C.B-17 controls. Two independently isolated embryo fibroblastic scid mouse cell lines display similar hypersensitivities to gamma-rays. In addition, these cell lines are sensitive to cell killing by bleomycin, which also produces DNA strand breaks, but not by the DNA crosslinking agent mitomycin C or UV irradiation. Measurement of the rejoining of gamma-ray-induced DNA double-strand breaks by pulsed-field gel electrophoresis indicates that these animals are defective in this repair system. This suggests that the gamma-ray sensitivity of the scid mouse fibroblasts could be the result of reduced repair of DNA double-strand breaks. Therefore, a common factor may participate in both the repair of DNA double-strand breaks as well as V(D)J rejoining during lymphocyte development. This murine autosomal recessive mutation should prove extremely useful in fundamental studies of radiation-induced DNA damage and repair.

Activated mouse peritoneal macrophages produce nitric oxide (NO) via a nitric oxide synthase that is inducible by interferon gamma (IFN-gamma): iNOS. We have studied the mechanisms by which transforming growth factor beta 1 (TGF-beta) suppresses IFN-gamma-stimulated NO production. TGF-beta treatment reduced iNOS specific activity and iNOS protein in both cytosolic and particulate fractions as assessed by Western blot with monospecific anti-iNOS immunoglobulin G. TGF-beta reduced iNOS mRNA without affecting the transcription of iNOS by decreasing iNOS mRNA stability. Even after iNOS was already expressed, TGF-beta reduced the amount of iNOS protein. This was due to reduction of iNOS mRNA translation and increased degradation of iNOS protein. The potency of TGF-beta as a deactivator of NO production (50% inhibitory concentration, 5.6 +/- 2 pM) may reflect its ability to suppress iNOS expression by three distinct mechanisms: decreased stability and translation of iNOS mRNA, and increased degradation of iNOS protein. This is the first evidence that iNOS is subject to other than transcriptional regulation.

Many Gram-negative pathogens assemble architecturally and functionally diverse adhesive pili on their surfaces by the chaperone-usher pathway. Immunoglobulin-like periplasmic chaperones escort pilus subunits to the usher, a large protein complex that facilitates the translocation and assembly of subunits across the outer membrane. The crystal structure of the PapD-PapK chaperone-subunit complex, determined at 2.4 angstrom resolution, reveals that the chaperone functions by donating its G(1) beta strand to complete the immunoglobulin-like fold of the subunit via a mechanism termed donor strand complementation. The structure of the PapD-PapK complex also suggests that during pilus biogenesis, every subunit completes the immunoglobulin-like fold of its neighboring subunit via a mechanism termed donor strand exchange.

To determine whether DNA polymerase eta plays a role in the hypermutation of immunoglobulin variable genes, we examined the frequency and pattern of substitutions in variable VH6 genes from the peripheral blood lymphocytes of three patients with xeroderma pigmentosum variant disease, whose polymerase eta had genetic defects. The frequency of mutation was normal but the types of base changes were different: there was a decrease in mutations at A and T and a concomitant rise in mutations at G and C. We propose that more than one polymerase contributes to hypermutation and that if one is absent, others compensate. The data indicate that polymerase eta is involved in generating errors that occur predominantly at A and T and that another polymerase(s) may preferentially generate errors opposite G and C.

Receptors for the Fc domain of IgG (Fc gamma R) provide a critical link between specific humoral responses and the cellular branch of the immune system. When hFc gamma R interact with immunoglobulin, a variety of biological responses are triggered. These include phagocytosis, endocytosis, antibody-dependent cellular cytotoxicity (ADCC), release of inflammatory mediators, and enhancement of antigen presentation. In the last few years our understanding of the Fc gamma receptor structure has increased dramatically, due to the availability of monoclonal antibodies (mAb) and cDNA probes. Fc gamma R are members of the immunoglobulin superfamily and three main classes, hFc gamma RI, hFc gamma RII, and hFc gamma RIII are recognized in man generating at least 12 different isoforms. A further level of complexity is introduced by various genetic polymorphisms and, importantly, recent evidence points at the relevance of this Fc gamma R heterogeneity.

Expression of proteins associated with immune function was investigated immunohistochemically in postmortem brain and spinal cord of patients with amyotrophic lateral sclerosis (ALS). Reactive microglia/macrophages displaying high levels of leukocyte common antigen (LCA), the immunoglobulin receptor Fc gamma R1, lymphocyte function associated molecule-1 (LFA-1), the complement receptors CR3 and CR4, the class II major histocompatibility complex molecules HLA-DR, HLA-DP and HLA-DQ and common determinants of the class I HLA-A,B,C complex were abundant in affected areas in ALS. These areas included the primary motor cortex, motor nuclei of the brain stem, the anterior horn of the spinal cord, and the full extent of the corticospinal tract. A significant number of T lymphocytes of the helper/inducer (CD4+) and cytotoxic/suppressor (CD8+) subtypes were observed marginating along the walls of capillaries and venules and extending into the parenchyma of affected areas. Clusters of complement activated oligodendroglia as well as degenerating neurites positive for C3d and C4d were frequently detected in ALS-affected areas. These data provide evidence of immune-effector changes in ALS. They are consistent with an autoimmune or slow virus theory of the disorder, but may reflect only secondary changes.

Maintenance of protective humoral immunity depends on the generation and survival of antibody-secreting cells. The bone marrow provides niches for long-term survival of plasma cells generated in the course of systemic immune responses in secondary lymphoid organs. Here, we have analyzed migratory human plasma blasts and plasma cells after secondary vaccination with tetanus toxin. On days 6 and 7 after immunization, CD19(+)/CD27(high)/intracellular immunoglobulin G(high) (IgG(high))/HLA-DR(high)/CD38(high)/CD20(-)/CD95(+) tetanus toxin-specific antibody-secreting plasma blasts were released in large numbers from the secondary lymphoid organs into the blood. These cells show chemotactic responsiveness toward ligands for CXCR3 and CXCR4, probably guiding them to the bone marrow or inflamed tissue. At the same time, a population of CD19(+)/CD27(high)/intracellular IgG(high)/HLA-DR(low)/CD38(+)/CD20(-)/CD95(+) cells appeared in the blood in large numbers. These cells, with the phenotype of long-lived plasma cells, secreted antibodies of unknown specificity, not tetanus toxoid. The appearance of these plasma cells in the blood indicates successful competition for survival niches in the bone marrow between newly generated plasma blasts and resident plasma cells as a fundamental mechanism for the establishment of humoral memory and its plasticity.

BACKGROUND

A diagnosis of chronic lymphocytic leukemia (CLL) requires a count of over 5000 circulating CLL-phenotype cells per cubic millimeter. Asymptomatic persons with fewer CLL-phenotype cells have monoclonal B-cell lymphocytosis (MBL). The goal of this study was to investigate the relation between MBL and CLL.

METHODS

We investigated 1520 subjects who were 62 to 80 years of age with a normal blood count and 2228 subjects with lymphocytosis (>4000 lymphocytes per cubic millimeter) for the presence of MBL, using flow cytometry. Monoclonal B cells were further characterized by means of cytogenetic and molecular analyses. A representative cohort of 185 subjects with CLL-phenotype MBL and lymphocytosis were monitored for a median of 6.7 years (range, 0.2 to 11.8).

RESULTS

Monoclonal CLL-phenotype B cells were detected in 5.1% of subjects (78 of 1520) with a normal blood count and 13.9% (309 of 2228) with lymphocytosis. CLL-phenotype MBL had a frequency of 13q14 deletion and trisomy 12 similar to that of CLL and showed a skewed repertoire of the immunoglobulin heavy variable group (IGHV) genes. Among 185 subjects presenting with lymphocytosis, progressive lymphocytosis occurred in 51 (28%), progressive CLL developed in 28 (15%), and chemotherapy was required in 13 (7%). The absolute B-cell count was the only independent prognostic factor associated with progressive lymphocytosis. During follow-up over a median of 6.7 years, 34% of subjects (62 of 185) died, but only 4 of these deaths were due to CLL. Age above 68 years and hemoglobin level below 12.5 g per deciliter were the only independent prognostic factors for death.

CONCLUSIONS

The CLL-phenotype cells found in the general population and in subjects with lymphocytosis have features in common with CLL cells. CLL requiring treatment develops in subjects with CLL-phenotype MBL and with lymphocytosis at the rate of 1.1% per year.

Myeloma, hybridoma, and thymoma cell lines have been successfully transfected for the Escherichia coli xanthine-guanine phosphoribosyltransferase gene (gpt) by using the plasmid vector pSV2-gpt. The transformed cells synthesize the bacterial enzyme 5-phospho-alpha-D-ribose-1-diphosphate:xanthine phosphoribosyltransferase (XGPRT; EC 2.4.2.22) and have been maintained in selective medium for over 4 months. Lymphoid cell lines expressing a K immunoglobulin light chain were obtained by transfecting cells with pSV2-gpt containing a rearranged K light chain genomic segment from the S107 myeloma cell line. The S107 light chain is synthesized in gpt-transformed J558L myeloma cells and is identical to the light chain synthesized by the S107 myeloma cell line, as judged by immunoprecipitation and two-dimensional gel electrophoresis. Furthermore, this light chain is synthesized and secreted as part of an intact antibody molecule by transformed hybridoma cells that normally secrete an IgGl (gamma, K) antibody molecule. No light chain synthesis was detected in a similarly transformed rat myeloma or a mouse thymoma line.

A glycoprotein with affinity for the Fc region of immunoglobulin was isolated from extracts of cultured cells infected with herpes simplex virus type 1, and experiments were done to characterize its properties and to investigate whether it could account for the Fc-binding activity previously demonstrated on the surfaces of intact herpes simplex virus-infected cells. The technique of affinity chromatography was used to identify and isolate the Fc-binding glycoprotein and to demonstrate the specificity of its interaction with immunoglobulin G-Fc. Although three electrophoretically distinguishable Fc-binding polypeptides were identified by affinity chromatography, these three species appear to be different forms of the same translation product, based on comparisons of proteolytic digestion products and on the kinetics of appearance of each form after a brief pulse with radioactive amino acids. The results suggest that one polypeptide, designated pE, is processed to yield gE1, which is in turn processed to yield gE2. Both gE1 and gE2 are glycosylated membrane proteins and both can be labeled by the lactoperoxidase-catalyzed radioiodination of intact infected cells, indicating the presence of these proteins in surface membranes of the cells. Increases in the amounts of gE1 and gE2 at the cell surface were found to parallel the increase in Fc-binding activity of intact infected cells.

OBJECTIVE

Neuromyelitis optica (NMO) immunoglobulin G (IgG) (aquaporin-4 [AQP4] IgG) is highly specific for NMO and related disorders, and autoantibody detection has become an essential investigation in patients with demyelinating disease. However, although different techniques are now used, no multicenter comparisons have been performed. This study compares the sensitivity and specificity of different assays, including an in-house flow cytometric assay and 2 commercial assays (ELISA and transfected cell-based assay [CBA]).

METHODS

Six assay methods (in-house or commercial) were performed in 2 international centers using coded serum from patients with NMO (35 patients), NMO spectrum disorders (25 patients), relapsing-remitting multiple sclerosis (39 patients), miscellaneous autoimmune diseases (25 patients), and healthy subjects (22 subjects).

RESULTS

The highest sensitivities were yielded by assays detecting IgG binding to cells expressing recombinant AQP4 with quantitative flow cytometry (77; 46 of 60) or visual observation (CBA, 73%; 44 of 60). The fluorescence immunoprecipitation assay and tissue-based immunofluorescence assay were least sensitive (48%-53%). The CBA and ELISA commercial assays (100% specific) yielded sensitivities of 68% (41 of 60) and 60% (36 of 60), respectively, and sensitivity of 72% (43 of 60) when used in combination.

CONCLUSIONS

The greater sensitivity and excellent specificity of second-generation recombinant antigen-based assays for detection of NMO-IgG in a clinical setting should enable earlier diagnosis of NMO spectrum disorders and prompt initiation of disease-appropriate therapies.

OBJECTIVE

Antibody responses to certain microbial antigens define heterogeneous groups of Crohn's patients; multiple and high-level responses to these antigens are associated with aggressive clinical phenotypes. The flagellin, CBir1, identified by investigations in the C3H/HeJBir mouse model, has been identified as a dominant antigen capable of inducing colitis in mice and eliciting antibody responses in a subpopulation of patients with Crohn's disease (CD). The aim of this study was to evaluate serum response to CBir1 flagellin in CD patients and to compare this response to responses defined previously to oligomannan (anti-Saccharomyces cerevisiae antibody), I2, OmpC, and neutrophil nuclear autoantigens (pANCA), and to determine anti-CBir1-associated phenotypes.

METHODS

A total of 484 sera from the Cedars Sinai Medical Center repository, previously typed for anti-Saccharomyces cerevisiae antibody, anti-I2, anti-OmpC, and pANCA were tested for anti-CBir1 by enzyme-linked immunosorbent assay, and results were assessed for clinical phenotype associations.

RESULTS

The presence and level of immunoglobulin G anti-CBir1 were associated with CD independently. Anti-CBir1 was present in all antibody subgroups and expression increased in parallel with increases in the number of antibody responses. pANCA+ CD patients were more reactive to CBir1 than were pANCA+ ulcerative colitis patients. Anti-CBir1 expression is associated independently with small-bowel, internal-penetrating, and fibrostenosing disease features.

CONCLUSIONS

Serum responses to CBir1 independently identify a unique subset of patients with complicated CD. This bacterial antigen was identified in a murine model and has a similar pattern of aberrant reactivity in a subset of CD patients.

Uracil in DNA results from deamination of cytosine, resulting in mutagenic U : G mispairs, and misincorporation of dUMP, which gives a less harmful U : A pair. At least four different human DNA glycosylases may remove uracil and thus generate an abasic site, which is itself cytotoxic and potentially mutagenic. These enzymes are UNG, SMUGG and MBD4. The base excision repair process is completed either by a short patch- or long patch pathway, which largely use different proteins. UNGG mispairs and possibly U in single-stranded DNA. SMUGGG in repair of U : G mismatches and single-stranded DNA. TDG and MBD4 may have specialized roles in the repair of U and T in mismatches in CpG contexts. Recently, a role for UNGimmunoglobulin diversification. Studies are now underway to examine whether mice deficient in Ung develop lymphoproliferative malignancies and have a different life span.

We determined the half-lives of several sets of murine monoclonal antibodies spanning all immunoglobulin isotypes in the serum. The antibodies in each set possess the same V region. With this approach, the differences in half-life observed between the different isotypes are independent of the V region carried by the monoclonal antibodies and therefore must relate to each other in the same way as the half-lives of each class of serum immunoglobulins. The half-life of a monoclonal antibody of the gamma 2a isotype is identical to the average half-life of serum IgG2a as previously determined (6-8 days; P. Vieira and K. Rajewsky, Eur. J. Immunol. 1986. 16:871). Therefore, the half-lives determined with monoclonal antibodies possessing the same V region represent the half-life of the serum immunoglobulins. In this way we calculated the half-life of IgM as 2 days, IgG3 and IgG1 as 6-8 days, IgG2b has a half-life of 4-6 days. IgE has a half-life of 12 h. A polymeric form of IgA was found to be eliminated from the serum with a half-life of 17-22 h.

Using immunoblots, we identified proteins of Borrelia burgdorferi bound by IgM and IgG antibodies during Lyme disease. In 12 patients with early disease alone, both the IgM and IgG responses were restricted primarily to a 41-kD antigen. This limited response disappeared within several months. In contrast, among six patients with prolonged illness, the IgM response to the 41-kD protein sometimes persisted for months to years, and late in the illness during arthritis, a new IgM response sometimes developed to a 34-kD component of the organism. The IgG response in these patients appeared in a characteristic sequential pattern over months to years to as many as 11 spirochetal antigens. The appearance of a new IgM response and the expansion of the IgG response late in the illness, and the lack of such responses in patients with early disease alone, suggest that B. burgdorferi remains alive throughout the illness.

Through the use of absorbed idiotypic antisera prepared against single isolated monoclonal IgM anti-gamma-globulins, partial cross-idiotypic specificity was demonstrated with other IgM anti-gamma-globulins. Such antisera classified these proteins into at least three groups. The major group which included 60% of the anti-gamma-globulins was particularly homogeneous. The anti-gamma-globulin specific antigens were detected best in hemagglutination and hemagglutination inhibition systems. They were not found in monoclonal IgM proteins that lacked anti-gamma-globulin activity although related antigens were detected at low concentrations in pooled immunoglobulin preparations as well as in heterogeneous anti-Rh antibodies. Several lines of evidence were obtained indicating that the antibody combining site was involved in the specific determinants. Attempts were made to analyze the fine specificity of each anti-gamma-globulin for the Fc fragment of different subclasses of human immunoglobulins as well as those of other species. Differences were observed but these were not readily related to the cross-specificity antigens. The anti-gamma-globulin specific antigens were very analogous to those previously described for monoclonal IgM cold agglutinins. Although each protein could be distinguished from all the others on the basis of individual idiotypic antigens, the antigens common to the specific groups of proteins with each of these activities were prominent and readily detected with multiple antisera. The results indicate basic similarities between proteins of a given activity even in unrelated individuals.

Mast cells are primary effectors in allergic reactions, and may have important roles in disease by secreting histamine and various inflammatory and immunomodulatory substances. Although they are classically activated by immunoglobulin (Ig)E antibodies, a unique property of mast cells is their antibody-independent responsiveness to a range of cationic substances, collectively called basic secretagogues, including inflammatory peptides and drugs associated with allergic-type reactions. The pathogenic roles of these substances have prompted a decades-long search for their receptor(s). Here we report that basic secretagogues activate mouse mast cells in vitro and in vivo through a single receptor, Mrgprb2, the orthologue of the human G-protein-coupled receptor MRGPRX2. Secretagogue-induced histamine release, inflammation and airway contraction are abolished in Mrgprb2-null mutant mice. Furthermore, we show that most classes of US Food and Drug Administration (FDA)-approved peptidergic drugs associated with allergic-type injection-site reactions also activate Mrgprb2 and MRGPRX2, and that injection-site inflammation is absent in mutant mice. Finally, we determine that Mrgprb2 and MRGPRX2 are targets of many small-molecule drugs associated with systemic pseudo-allergic, or anaphylactoid, reactions; we show that drug-induced symptoms of anaphylactoid responses are significantly reduced in knockout mice; and we identify a common chemical motif in several of these molecules that may help predict side effects of other compounds. These discoveries introduce a mouse model to study mast cell activation by basic secretagogues and identify MRGPRX2 as a potential therapeutic target to reduce a subset of drug-induced adverse effects.