Several types of virus particles including retroviruses and herpes viruses can impede the ability of human peripheral blood lymphocytes to respond to mitogenic stimuli. This is true even in the case of viruses that have been inactivated by u.v. light, indicating that the mechanisms involved are infection independent, at least in part. The observed inhibition could be shown to correlate with a reduced level of production of TCGF activity in the virus co-incubated cultures. In addition, these same viruses are apparently able to complex directly with TCGF activity and to render it biologically inactive. This was shown by allowing known quantities of virus to interact with TCGF activity for different periods of time, followed by centrifugation of any virus-TCGF complexes. This interference is reversible, however, and the dissociation of these virus-TCGF complexes by mild detergent, followed by viral centrifugation, yields TCGF activity in the supernatant.

A limiting dilution assay was used to determine the frequencies of T cells that could be induced to proliferate and kill by Con A and TCGF. The frequency of proliferating cells was 1 in 5 nylon wool-purified spleen cells and 1 in 7 normal lymph node cells. The frequencies in the same cell populations of lectin-dependent killer cell precursors were 1 in 5 and 1 in 9, respectively. Even at limiting numbers of T cells seeded per culture, very few cultures proliferated without showing cytotoxic activity. Thus, under these conditions Con A and TCGF, preferentially if not exclusively, activate T cells that will kill in the presence of PHA. This experimental system can be used for estimating the repertoires of specific CTL-precursors activated by Con A and expanded in TCGF.

Total lymphoid irradiation (TLI) was administered to (BALB/c X C57BL/6)F1 mice in eight daily doses of 200 rad (total 1600 rad). Spleen cells isolated from mice after treatment with TLI do not respond to alloantigens in vitro in a one-way mixed lymphocyte reaction (MLR), but normal reactivity recovers after approximately 2 mo. Radioresistant, antigen-nonspecific suppressor cells are documented in the spleens of TLI-treated mice immediately after radiotherapy, but suppressive capacity gradually disappears within 30 days. After TLI, the spleen is repopulated with large cells, the proportion of which is greatest at a time when theta-bearing cells are still depleted. Radioresistant suppression is mediated predominantly by the large cell subset and is thymus independent. Suppressor function can be abolished by lethal physicochemical procedures including formaldehyde fixation, multiple freeze-thawing, and heating to 56 degrees C, and it cannot be conferred by supernatants of TLI-suppressed MLR suspensions. Suppression cannot be overcome by adding various cell factors including T cell growth factor (TCGF) and lymphocyte-activating factor (LAF), nor is it affected by a prostaglandin inhibitor. Equally potent radioresistant suppressive activity is documented by co-culturing cells derived from other sources enriched in large, immature hematopoietic cells, including fetal liver cells and bone marrow cells obtained from normal and congenitally athymic mice. The presence of a large cell population and MLR suppressor function is also documented in the spleens of mice treated with single dose or fractionated doses of lethal whole body irradiation, followed by reconstitution with bone marrow cells obtained from normal mice. The data suggest that MLR suppressor cells, which are large, immature and predominantly radioresistant, can be induced after a short and well-tolerated TLI regimen.

Mouse and human lymphoid cells were cultivated in the presence of T-cell growth factor (TCGF) and evaluated for their in vivo anti-tumor effect in mice. Cultured spleen cells of normal BALB/c mice or of mice bearing the M109 tumor had a high level of cytotoxic activity in vitro against a variety of tumor target cells and had characteristics of natural killer cells. These cultured cells were evaluated for their in vivo cytotoxic activity by a mixture with [125I]dUrd-labelled M109 tumor cells (2 x 10(5)) at a 30:1 ratio and inoculation of the mixture into the footpads of BALB/c mice. The level of radioactivity remaining in the footpad was determined at various periods following inoculation of radiolabelled tumor cells. The presence of cultured cells in the inocula caused a marked decrease in the footpad radioactivity by 24 h. However, the slope of clearance of the radiolabel then became similar to that in the control mice. The cultured cells delayed, but did not prevent, tumor appearance, and did not influence the subsequent rate of growth of the tumors. The transient effects of the cultured cells contrasted with the more prolonged in vivo effects of alloimmune lymphocytes, and this may be due to their short survival period. Ninety-nine percent of [125I]dUrd-labelled cultured mouse lymphoid cells were eliminated within 48 h of i.f.p. inoculation. Cultured human lymphoid cells, initiated from the blood of normal donors, also had a high level of cytotoxic activity in vitro and were evaluated for their in vivo effects by intra-footpad inoculation into nude mice, together with radiolabelled human tumor cell lines, G-11 or HT-29. In vivo cytotoxic activity of the human cultured lymphoid cells correlated with their cytotoxic effect in vitro. These results indicate that cultured mouse an human effector cells have appreciable in vivo cytotoxic effects against tumor cell lines. However, the transient duration of these effects may limit their immunotherapeutic potential.

The effects of eliminating cycling precursors by in vivo administration of high doses of hydroxyurea (HU) in populations of mouse spleen T lymphocytes were studied by membrane immunofluorescence identifying mature Thy 1+, Lyt 2- and Lyt 2+ cell populations and mitogen-induced T-cell growth factor (TCGF) production or reactivity to TCGF. HU treatment results in a sharp decrease in the total number of T cells in mouse spleen, indicating that about 50% of peripheral splenic T lymphocytes have a short survival time in vivo. This depletion is more marked for Lyt 2+ cells than for Lyt 2- cells. The decay of TCGF-reactive spleen cells after drug administration is similar to that of the overall spleen T-cell population. Conversely, production of TCGF induced by concanavalin A is predominantly affected by HU treatment, indicating a shorter life span of the cell(s) involved in TCGF production.

An human T-cell leukemia virus (HTLV)-producing cell line (Ra-1) was established from rabbit lymphocytes by co-cultivation with lethally irradiated MT-2 cells. Ra-1 cells were inoculated intravenously into a Japanese monkey and rabbits. All animals responded with the production of antibodies to HTLV. Lymphocytes from the seroconverted animals were grown in the presence of T-cell growth factor (TCGF) or co-cultured with lymphocytes from seronegative healthy persons. The TCGF-grown cells, which were chromosomally of the recipient type, expressed HTLV antigens and particles. The co-cultures gave rise to human T-cell lines which also harbored HTLV antigens and particles. Blood transfusion from the infected rabbits resulted in the seroconversion of the recipient rabbits. HTLV-producing lymphoid cell lines were established from some of the transfused rabbits. The recipient origin of these cell lines was determined by chromosome analysis. It was possible to serially transmit HTLV by blood transfusion in rabbits. Thus, these animals offer promise as a laboratory model for HTLV infection.

Cloned T cell lines from mixed lymphocyte cultures stimulated with autologous Epstein Barr virus- (EBV) transformed lymphoblastoid cell line (LCL) cells were established using a limiting dilution technique in the presence of T cell growth factor (TCGF). The T cell lines included two distinct clones of cytotoxic T cells (Tc) in addition to EBV-specific Tc. A cytotoxic profile of one cloned line was similar to that of endogenous NK cells in peripheral blood. The other cloned Tc line showed an anti-human cytotoxicity. The susceptible targets for this latter Tc line were various human cells, including autologous LCL and peripheral blood lymphocytes (PBL), stimulated with pokeweed mitogen, along with NK-sensitive and NK-resistant cell lines. Weak cytotoxic activity was detected against various xenogeneic cell lines. Furthermore, autologous and allogeneic cloned T cell lines were resistant to killing by the anti-human effector clone. These t wo distinct cloned Tc lines expressed the Leu-1 and Leu-2a antigens, which are markers of suppressor/cytotoxic T cells.

C57BL/6J nu/nu mice respond to the type 2 TI antigen DAGG-Ficoll, but not to the TD antigen SRC. A comparable difference can also be seen in vitro, but only at high spleen cell density and in the presence of selected batches of FBS. At low spleen cell density and in the absence of FBS, the DAGG-Ficoll-induced B cell response is strictly dependent on soluble helper factors or cloned specific helper T cells. The B cell response so induced requires that the T cell-depleted spleen cells be compatible in the I-A subregion of the H-2 complex. These helper factors, induced by antigen in an I-A-restricted T cell-macrophage interaction, provide helper for T cell-depleted spleen cells irrespective of their H-2 haplotype. Under conventional culture conditions, the stringent requirement for helper factors in the in vitro response to DAGG-Ficoll is obscured by FBS. In vitro culture of low numbers of spleen cells, in serum-free medium instead of FBS, provides a sensitive assay for helper factors. We have compared the helper activity for a B cell response to SRC or DAGG-Ficoll as provided by antigen-induced supernatants of various individual EA-specific T cell clones. There was a remarkable and consistent heterogeneity among individual T cell clones: their helper activity in the response to TI and TD antigens did not correlate, nor was there any correlation between helper activity and antigen-induced TCGF (interleukin 2) activity.

Recipients of marrow grafts from HLA-identical, (including MLC non-reactive) sibling donors have a 40-50% incidence of acute graft vs. host disease (GVHD); the involvement of non-HLA linked, minor histocompatibility antigens (miHA) has been implicated. One of the target tissues of GVHD is the skin where morphological analysis of biopsy specimens is often used to support this diagnosis. We have obtained skin biopsy specimens from the site of GVHD lesions, grown the cells in the presence of T cell growth factor (TCGF) and feeder cells, and tested these cultured cells in the primed lymphocyte test (PLT) and cell mediated lympholysis (CML) assay. Five of six cell cultures tested demonstrated secondary proliferative but not cytolytic reactivity; cells from one culture demonstrated both reactivities. The cell culture populations generated are presumably directed against non-HLA antigens, i.e., miHA whose expression is restricted by an HLA antigen of the recipient. The data are consistent with the suggestion that in the majority of these cultures, the restriction element may be a determinant encoded within the HLA-D region: DQ, DR, and possibly DP based on panel testing. Although the number of cases is small, these preliminary data demonstrate the feasibility of this type of culturing system and also suggest that the cellular immunological events leading to the manifestation of skin GVHD lesions may be predominantly a delayed type hypersensitivity reaction.

Of 12 T-lymphoma cell lines investigated, one line, EL-4 azgr (Thy-1+, Lyt-1+, Lyt-2-3-,Ia-, T-200+, sIg-, and FcR-) and, to a lesser extent, the parental cell line, EL-4, produced T cell growth factor(s) (TCGF) when stimulated by the T-cell mitogen concanavalin A (Con A). Induced production of TCGF-E was detected by 6 h and maximal at 18-24 h. Purified TCGF-E from this source had an approximately 30,000 mol wt and the biological activity of TCGF produced by whole spleen cells, including: augmentation of T cell-mitogen responses, cytotoxic T lymphocyte (CTL) proliferation support dependence, augmented generation of CTL, lack of strain specificity, and failure to stimulate resting T cells. TCGF-E is neither synthesized or secreted by this lymphoma cell line unless stimulated by Con A. X-irradiation up to 7,000 rad failed to inhibit synthesis and secretion. These observations have a practical application in providing a relatively homogeneous clonal cell product for T cell culture support and for structural and functional studies of the TCGF molecule(s). They suggest also a model for examining mechanisms of triggering production and secretion of a regulatory molecule that controls T cell functions.

Lymphocytes from a healthy HLA-identical bone marrow transplant donor were tested for their ability to destroy her brother's acute myelogenous leukemia blasts in vitro. Primary mixed lymphocyte culture (MLC) and cell-mediated lysis (CML) responses between the patient's remission (pretransplant) and donor's lymphocytes were negative. Stimulation of donor lymphocytes for 7 d in vitro with irradiated leukemia cells, leukemia cells plus allogeneic irradiated lymphocytes, or a pool of irradiated lymphocytes from 10 donors, did not activate any cytotoxic cells able to destroy the HLA identical leukemic blasts. Further culturing for 7 additional d in T cell growth factor (TCGF) generated lymphocytes that induced effective cytotoxicity against the leukemic blasts, but not against autologous lymphocytes. Effective killing against the leukemia was observed only in cultures initially stimulated with the irradiated leukemia cells. These cytotoxic cells were maintained in TCGF and mediated persistent killing against the leukemic target cells. They were also able to destroy lymphocytes from the patient's mother and father, but not from an unrelated cell donor. This suggested specific recognition of non-HLA antigens inherited by the patient, that were foreign to the HLA identical bone marrow donor. These lymphocytes were cloned by a limiting dilution technique and one clone maintained cytotoxicity to the AML blasts and the father's lymphocytes, but not lymphocytes from the mother or an HLA-identical donor. This cytotoxicity was inhibited by a monoclonal anti-HLA antibody. Thus, in vitro sensitization of this sibling's lymphocytes with AML blasts followed by TCGF expansion, and cloning, enabled the detection of HLA-restricted cytotoxic cells that recognize minor locus histocompatibility antigens. This immune recognition may be relevant to the "graft vs. leukemia" effect that has been observed in leukemic animals and patients following histocompatible hematopoietic transplants.

A system for routine long-term growth of human mature T-lymphocytes in liquid suspension culture was developed in our laboratory about 5 years ago. This system involves the continuous use of a factor, termed T-cell growth factor (TCGF) for the propagation of T-lymphocytes previously activated by lectin (PHA or Con A) or by antigen. Normal human T cells do not respond to TCGF unless they are first activated to become blast cells by antigen or lectin, presumably because they do not contain TCGF receptors until activated. We think then that TCGF is the physiological growth promoter in the immune response of T-lymphocytes, acting as the second signal (after antigen) in the immune response. These T cells show functional features, e.g., cytotoxic or helper function and other evidence of maturity. By using purified TCGF free of PHA and of lymphokines other than TCGF, we have recently been able to grow routinely neoplastic T cells from patients with leukemias and lymphomas of mature T cells, e.g., from patients with the Sezary syndrome and those with mycosis fungoides (cutaneous T-cell leukemias and lymphomas). Of considerable interest, the neoplastic T cells respond directly to TCGF; unlike normal T Cells they do not require prior in vitro activation with antigen or lectin. This indicates that transformed mature T cells already express TCGF receptors. This may be an important functional difference between normal and transformed human T cells. From some of these new cell lines we have recently isolated a new class of RNA tumor viruses (retroviruses), which we call HTLV. For several reasons we believe these are the first unambiguous isolates of RNA tumor viruses from humans. For instances, we now have data that these new viruses are easily distinguishable from all previously isolated viruses from animals. In addition, we have found antibodies in sera of some patients with these diseases specifically reactive with proteins of these viruses.

One-day-old chicks with no maternal antibodies to chicken anemia agent (CAA) were inoculated intramuscularly with CAA grown in MDCC-MSB1 cells. A control group of birds from the same source was inoculated intramuscularly with a lysate from uninfected MSB1 cells. Birds were killed at 8, 15, 22, 29, and 43 days postinoculation (PI), and the spleens were removed. Spleen cells were dispersed and stimulated with various concentrations of Concanavalin A (Con A), and lymphocyte transformation responses were determined. Supernatants from Con A-stimulated cultures were assayed for T-cell growth factor (TCGF) and interferon. Decreased lymphocyte transformation and TCGF production were demonstrated at 8 and 15 days PI. This was followed by a stimulation in activities before a return to control levels at 43 days PI. Interferon levels were elevated 8 days after infection. This was followed by a significant decrease in activity compared with controls at 15, 22, and 29 days PI, and a return to control levels by 43 days PI. The results suggest that CAA infection in young chickens can produce a dramatic decrease in immune competence, which, although transitory, is likely to seriously compromise the ability of birds to mount a successful immune response to invading pathogens.

These studies present an efficient and sensitive method for detection of T cell growth factor (TCGF) activity in human lymphocyte cultures and illustrate that T cell growth factors are associated with T lymphocyte-mediated anti-HSV-1 responses. Secretion of TCGF is induced after stimulation of human peripheral blood mononuclear cells ( PBMNC ) with herpes simplex virus type 1 (HSV-1). Lymphokine activity is detected in a simple, sensitive method by studying [3H]thymidine incorporation after the addition of murine CTLL -20 cells to cultures of gamma-irradiated (4000 R), virus-stimulated PBMNC . By using this assay, we find that PBMNC from seropositive but not seronegative individuals produce detectable TCGF activity in a dose-dependent manner after incubation with HSV-1. Maximum activity is detected between 24 to 48 hr of incubation and correlates with in vitro proliferation of nonirradiated PBMNC in response to the virus. In addition, gamma-irradiated (1000 to 3000 R) PBMNC , which are frequently used as a source of antigen-presenting cells (APC), can secrete TCGF after contact with HSV-1. Lymphokine production by the APC-containing population is eliminated by gamma-irradiation (5000 R); such APC can still present UV-inactivated HSV-1 to HSV-1-responsive lymphoblasts, indicating that lymphokine production by T cells residing in the APC population is not essential for antigen presentation.

A T-cell line of mixed phenotype (60% L3T4+, 40% Lyt-2+) was isolated from mice infected with Mycobacterium bovis (BCG). This line responded to M. lepraemurium and BCG but not to M. leprae and produced TCGF spontaneously. It also produced factors which stimulated macrophages to secrete hydrogen peroxide and superoxide anion. In vivo studies showed that only L3T4+ cells were required to transfer DTH responses and that Lyt-2+ cells suppressed this response. Both L3T4+ and Lyt-2+ cells were required to inhibit M. lepraemurium multiplication in vivo.

The effect of xenogeneic anti-Thy-1 antibody on T cell growth factor (TCGF) production by T lymphoma cell lines has been examined as a model system for T cell activation. EL-4 G12 (a cloned subline of the producer EL-4 azgr cell line) produced TCGF when stimulated by a high concentration of anti-Thy-1, but none was induced by low concentrations of anti-Thy-1. Large amounts of TCGF were produced when these cells were cultured with Fc-receptor positive (FcR+) accessory cells. TCGF production by EL-4 G12 showed dose response kinetics similar to TCGF production by anti-Thy-1-stimulated, purified normal spleen T cells. Goat anti-rabbit IgG (GaRIG) and protein A substituted for this accessory helper effect, but neither FcR+ cells nor Protein A worked when (Fab')2 anti-Thy-1 was used instead of IgG anti-Thy-1. Anti-T-200 monoclonal antibody inhibited anti-Thy-1-induced TCGF production by EL-4 G12 and accessory cells. Phorbol myristic acetate and lymphocyte-activating factor also substituted in part for the accessory cell help. The data suggest there are at least 2 different accessory cell help mechanisms in anti-Thy-1-induced TCGF production, anti-Thy-1-bound membrane aggregation either by GaRIG, Protein A or FcR, and a LAF-dependent mechanism.

Activation of T- and B-lymphocytes by a variety of immunological stimuli has been reported to induce specific insulin receptors. The purpose of the present work was to determine whether glucagon receptors are also induced in activated cells. Studies of glucagon and insulin receptors were carried out using normal human mononuclear cells activated by phytohemagglutinin or T-cell growth factor (TCGF), as well as established B- and T-lymphoblastoid cell lines. With phytohemagglutinin, glucagon and insulin binding increased 15- and 36-fold, respectively, and peaked after 5 days in parallel with the rise in thymidine incorporation. Increased binding was associated with an increase in the number of receptors, most marked for insulin, though affinity for the insulin receptor was decreased. Normal human mononuclear cells cultured with TCGF showed an early modest rise in insulin binding due to increased receptor number, without a change in affinity, and a striking and progressive rise up to 50-fold in glucagon binding due to both increased receptor number and affinity. The differences in receptor response to these T-cell mitogens suggest that TCGF selects out a T-lymphoblast subset with very high glucagon receptors. B- and T-lymphoblastoid cells showed patterns of glucagon and insulin receptors that appear to be characteristic for each cell type. Glucagon binding was 7-fold higher (P less than 0.01), while inulin binding was 7-fold lower (P less than 0.01) in T- vs. B-lymphoblastoid cells. T-Cell lines had twice the number of glucagon receptors, whereas B-lines had 4-fold the number of insulin receptors, with much greater affinity for insulin compared with T-line insulin receptors. Induction of both insulin and glucagon receptors on activated lymphoblasts suggests that these receptors may play a significant role in cell function.

T cell growth factor (TCGF) has become a valuable means of maintaining T lymphocytes in long-term culture and of studying T cell function. Numerous problems have been met in the production of TCGF of consistently good quality and in the maintenance of human T cell lines over long periods. We have investigated optimal conditions for TCGF production, and simplified assay systems for TCGF activity. The best TCGF production was obtained by short-term treatment with high concentrations of phytohemagglutinin (PHA). The TCGF producing lymphocytes could be re-used for TCGF production up to 1 month after the first treatment course. Human cultured T cell lines, fresh lymphocytes, short-term PHA stimulated lymphocytes and cultured marmoset T lymphocyte lines were all used for assay of TCGF. We recommend PHA stimulation of human lymphocytes for this assay on a routine basis, comparing results with a standard TCGF batch and calculating a growth index. Adherent cells impair TCGF production. Optimal TCGF production was seen when lymphocyte preparations without adherent cells from different donors were used.

The roles of accessory cells and T cell-growth factor (TCGF) in the in vivo induction of herpes simplex type 1 (HSV) specific cytotoxic lymphocytes (CTL) were evaluated. Spleen cells from animals infected with HSV 4-6 weeks previously were depleted of adherent cells by passage over Sephadex G10. Unlike intact cells, such depleted spleen cells failed to respond by producing H-2 restricted virus-specific CTL upon culture for 5 days with infectious HSV. The CTL response could be restored either by adding normal genetically compatible peritoneal cells as accessory cells or by the addition of TCGF. To obtain optimum restoration accessory cells needed to be added soon after culture initiation but with TCGF addition, partial restoration was evident when added as late as 72 hr after culture. TCGF also permitted intact spleen cells to respond to heat-inactivated virus. The results are interpreted to indicate that accessory cells are essentially required for the presentation of virus to specific helper cells with such cells responding by the production of TCGF. The results also indicate that certain forms of virus may trigger the response of CTL precursors but not the response of helper cells.

Three cell lines of mature T cell origin established from patients with cutaneous T cell lymphoma-leukemia (CTCL) have been found to be constitutive producers of TCGF (L-TCGF). Biologically active L-TCGF can also be eluted from the plasma membranes of these cells. We have compared the biologic and biochemical properties of L-TCGF and TCGF derived from normal lymphocytes (N-TCGF). L-TCGF and N-TCGF share similar biologic activity: both support long-term growth of T cells that have undergone prior lectin or antigen stimulation, and have no effect on unstimulated T cells. However, L-TCGF is a more acidic (pI 4.5 vs 6.5 to 8.0) molecule than N-TCGF and elutes from DEAE-Sepharose at higher salt concentration (0.2 M NaCl vs 0.07 to 0.1 M NaCl). In addition, these two factors display differing mobilities on gel filtration. Treatment of L-TCGF with neuraminidase or alkaline phosphatase does not alter its pI, indicating that enzymatically vulnerable sialic acid or phosphate groups are not involved in the variation. The nature and significance of this biochemical variant remain unknown.

Mitogen-free and serum-free supernatants (SNs) from cultures of phytohaemagglutinin (PHA)-stimulated Xenopus splenocytes, co-stimulated thymocytes, induced proliferation of splenic and thymic lymphoblast and supported growth of alloreactive T-cell lines. These SNs had no effect on 'resting' splenocytes, as measured by uptake of tritiated thymidine ([3H]TdR). Growth-promoting activity was also detected in SNs of cultures containing alloreactive T-cell lines and either PHA or irradiated stimulator cells that expressed the original priming alloantigens. Thus, T lymphocytes appear to be involved in producing, as well as responding to, a Xenopus T-cell growth factor (TCGF). TCGF activity could be absorbed from these active SNs with PHA-activated splenic blasts. No functional cross-reactivity among different mammalian interleukin-2 (IL-2) and Xenopus TCGF preparations was detected.

Isoelectric focusing demonstrated that T cell growth factor (TCGF), T cell replacing factor (TRF), and granulocyte-macrophage colony-stimulating factor (GM-CSF) derived from concanavalin A-stimulated T cell hybridomas and spleen cells are heterogeneous with respect to charge. The spleen cell-derived TCGF and TRF activities focused with isoelectric points (pI) between 3.5 and 6.5 whereas the range for GM-CSF activity was broader (pI, 3.5 to 8.0). The T cell hybridoma-derived activities were slightly more acidic. Neuraminidase treatment of both hybridoma 123 and spleen cell-derived material resulted in a major peak of each activity (TRF/TCGF pI, 4.9; GM-CSF pI, 4.7). Neuraminidase treatment of hybridoma T6-derived material resulted in peaks of TRF and TCGF around 6.0 as well as one around 5.0, suggesting that this charge heterogeneity was due to causes other than variations in the level of sialic acid on the relevant molecules. Tunicamycin-treated spleen cells or hybridoma 123 cells released biologically active TCGF, TRF, and GM-CSF. Each of these three activities from tunicamycin-treated spleen cells focused with pI around 5.0. A major fraction of TRF, TCGF, and GM-CSF activities bound to wheat-germ agglutinin. GM-CSF also bound to concanavalin A and lentil lectin. These results suggest that the molecules responsible for TCGF, TRF, and GM-SCF activities are glycosylated and that the observed heterogeneity in charge and lectin-binding characteristics is due in part to variable glycosylation. Glycosylation was not critical for any of the three biologic activities. No conclusive separation of TRF and TCGF activities was observed in these experiments although GM-CSF differed from TRF and TCGF in that it bound to Concanavalin A.

The accessory cell requirements of human neonatal T lymphocytes were compared with those of adult T lymphocytes in lectin-induced polyclonal activation. It was found that purified neonatal Esh rosette positive lymphocytes were not activated into a proliferative response by the lectin phytohaemagglutinin (PHA), by phorbol ester (TPA) or by conditioned medium containing T cell growth factor activity (TCGF-CM). A proliferative response to PHA was obtained in the presence of a suitable accessory cell (AC) such as the plastic adherent, monocyte enriched population or the sIg positive lymphocyte population, both of which were shown by cellular titrations to be equally effective. Optimal proliferative responses to PHA could also be obtained, in the absence of accessory cells, by addition of TPA or TCGF-CM. Neonatal T lymphocytes gave highly reproducible responses and this could be achieved effectively by simple separation procedures not involving further subfractionation of the responding Esh+ lymphocyte population. The exquisite accessory cell dependence of these cells demonstrated in this investigation provides a readily available human model system for the evaluation of the variables involved in T lymphocyte activation and a sensitive assay for measuring accessory cell activity.