Suppressor T cells activated by autologous B-cell derived lines inhibit blastogenic responses by peripheral lymphocytes to mitogens or autologous lymphoblastoid cell lines

EBV-transformed B-cell lines (LCL) suppressed peripheral lymphocyte responses to mitogens (PHA, PWM, and protein A). Cell separation experiments have shown that LCL cells activate autologous radiosensitive suppressor T cells that inhibit T-cell responses to mitogens (PHA and Con A) and to the autologous lymphoblastoid cell line itself. The significance of this autologous response and the way it may reflect on the effect of the suppressor T cells on the regulation of potential autoimmune responses is considered in relation to the in vivo phenomena observed in the course of acute mononucleosis.     

Two phenotypically distinct suppressor T cell subpopulations inhibit the induction of B cell differentiation by phytohemagglutinin

Human B lymphocytes can be induced to differentiate into antibody-secreting plasma cells by Leu-3+ T lymphocytes stimulated with pokeweed mitogen (PWM), a polyclonal T cell activator. In contrast, other polyclonal T cell mitogens, such as phytohemagglutinin (PHA), also activate Leu-3+ T cells but are relatively ineffective inducers of B cell differentiation. We have performed a series of experiments to investigate the mechanism underlying this apparent paradox. When human B cells were cultured with unfractionated T cells and PWM or PHA, only PWM was able to induce plasma cell formation and immunoglobulin (Ig) secretion. However, when the T cells were treated with mitomycin C (MMC) before culture, both PWM and PHA were able to induce significant B cell differentiation. These data indicated that both mitogens were able to activate the helper T cells required for B lymphocyte differentiation and suggested that MMC-sensitive suppressor T cells were responsible for inhibiting the induction of antibody-secreting cells by MMC-untreated T cells stimulated with PHA. Phenotypic analysis of the T cells capable of suppressing PHA-induced B cell differentiation revealed that small numbers of either Leu-2+ or Leu-3+ T cells could profoundly suppress the B cell differentiation induced by PHA. In contrast, significant suppression of PWM-stimulated B cell differentiation was observed only with relatively large numbers of Leu-2+ T cells. These data confirm previous reports that OKT4+/Leu-3+ T cells can suppress human B cell differentiation and indicate that the difference in B cell differentiation induced by PWM and PHA with MMC-untreated T cells is largely a reflection of the relative potency of these mitogens to activate these phenotypically distinct suppressor T cell subpopulations.     

Secretions of anti-myelin-associated glycoprotein antibodies by B cells from patients with neuropathy and nonmalignant monoclonal gammopathy

Four patients with peripheral neuropathy and nonmalignant monoclonal gammopathy with anti-myelin-associated glycoprotein (MAG) antibodies were studied to determine whether secretion of anti-MAG IgM antibodies by B cells was autonomous, or whether the monoclonal B cells were responsive to T cells. Secretion of anti-MAG IgM by isolated B cells was stimulated by the addition of increasing numbers of pokeweed mitogen (PWM)-activated autologous OKT4+ helper T cells in all four patients. Secretion of anti-MAG IgM by peripheral blood lymphocytes was dependent on the ratio of OKT4+ T helper cells to OKT8+ T suppressor/cytotoxic cells. In three patients with an OKT4+ to OKT8+ T-cell ratio of 2:1, PWM activation stimulated secretion of anti-MAG IgM; in one patient with an OKT4+ to OKT8+ ratio of 1:2, activation by PWM suppressed anti-MAG IgM secretion. These studies suggest that the monoclonal B cells that secrete anti-MAG IgM are responsive to regulatory T cells.     

Effect of monoclonal antibodies (MoAb) to class I and class II HLA antigens on lectin- and MoAb OKT3-induced lymphocyte proliferation

We have examined the effect of several monoclonal antibodies (MoAb) to monomorphic determinants of class II HLA antigens, and MoAb to monomorphic determinants of class I HLA antigens and to beta-2-microglobulin (beta 2-mu) on lectin- and MoAb OKT3-induced proliferation of human peripheral blood mononuclear cells (PBMNC) and cultured T cells (CTC). Some, but not all, anti-class II HLA MoAb inhibited the proliferative response of PBMNC to MoAb OKT3 and pokeweed mitogen (PWM). The degree of inhibitory effect varied considerably. This effect was not limited to anti-class II HLA MoAb since anti-class I HLA MoAb and anti-beta 2-mu MoAb also inhibited MoAb OKT3- or PWM-induced proliferative responses. In contrast, the response of PBMNC to phytohemagglutinin (PHA) and concanavalin A (Con A) was not blocked by any anti-class II HLA MoAb. However, some anti-class II HLA MoAb also inhibited the proliferative response of CTC plus allogeneic peripheral blood adherent accessory cells (AC) to PHA or Con A as well as to MoAb OKT3 or PWM. This may be attributable to the substantially greater class II HLA antigen expression by CTC than by fresh lymphocytes. Pretreatment of either CTC or AC with anti-class II HLA MoAb inhibited OKT3-induced proliferation. In contrast, pretreatment of CTC, but not AC, with anti-class I HLA MoAb inhibited the proliferative response of CTC to OKT3. Pretreatment of CTC with anti-class I HLA MoAb inhibited PHA-, Con A and PWM-induced proliferation, to a greater degree than the anti-class II HLA MoAb. It appears as if lymphocyte activation by different mitogens exhibits variable requirements for the presence of cells expressing major histocompatibility determinants. Binding of Ab to membrane markers may interfere with lymphocyte-AC cooperation, perhaps by inhibiting binding of mitogens to their receptors or by interfering with lymphocyte and AC function. We also have examined the role of class II HLA antigens on CTC by depleting class II HLA-positive cells. As expected, elimination of class II HLA-positive AC with anti-class II HLA MoAb plus complement caused a decrease in proliferation of CTC in response to all the mitogens tested. In contrast, elimination of class II HLA-positive CTC was shown to clearly increase proliferation of CTC, perhaps because this may deplete class II HLA-positive suppressor cells.     

Modulated immune responsiveness associated with experimental Encephalitozoon cuniculi infection in BALB/c mice

Spleen cell blastogenesis to mitogens and antibody responses to sheep erythrocytes (sRBC) were tested in BALB/c mice with experimental E. cuniculi infections. Blastogenesis responses of spleen cells 1 week post-infection were significantly lower than normal to T-cell mitogens (Con A and PHA) and were unchanged in response to B-cell mitogens (LPS and PWM). After 2 weeks post-infection, the responses to T cell mitogens returned to normal. Mixing spleen cells from 1-week infected mice with cells from uninfected mice failed to reveal the presence of suppressor cells. Antibody responses to sRBC were significantly slower to develop in 1 week-infected mice compared with uninfected mice or mice infected 2 weeks earlier or at the same time as sRBC challenge. Infected mice displayed splenomegaly which was most pronounced 1 week post-infection and the differential spleen cell counts revealed the presence of lymphoblasts. Lymphohyperplasia appeared to cause the splenomegaly. No shifts in the proportion of Thy 1.2+ T cells, Ig+ B cells, or esterase-positive macrophages were detected. These results indicate that the immune system in BALB/c mice is depressed early during E. cuniculi infections.     

Induction of suppressor cells to T- and B-cell proliferative responses and immunoglobulin production by monoclonal antibodies recognizing the CD3 T-cell differentiation antigen

Monoclonal antibodies (mAb's) recognizing the CD3 T-cell differentiation antigen induced the generation of suppressor cells. These cells inhibited (1) proliferative responses of human peripheral blood mononuclear cells (PBMC) to PHA and allogeneic cells in mixed leukocyte culture; (2) proliferative responses of purified E-rosette-negative cells to Staphylococcus aureus Cowans I; and (3) de novo immunoglobulin synthesis and secretion in the pokeweed mitogen (PWM)-induced differentiation system. Monoclonal antibodies recognizing other T-cell differentiation antigens (anti-Leu 2a, anti-Leu 3a, and anti-Leu 5) did not induce the generation of suppressor cells, even at very high antibody concentrations. Statistically significant differences were not observed in the ability of the OKT3 and anti-Leu 4 mAb's to induce suppressor cells. Monocytes were not required for the generation of anti-CD3-induced suppressor cells. F(ab')2 fragments of the OKT3 mAb's were equally effective when compared with intact antibody molecules in inducing suppressor cells, although they did not induce proliferative responses. Proliferation was not required for the induction of suppressor cells. Irradiation (2500 rad) of PBMC before incubation with the anti-CD3 mAb did not affect the generation of suppressor cells. Furthermore, anti-CD3-induced suppressor cells were radioresistant. Addition of recombinant IL-2 to the cultures of responding cells and suppressor cells did not reverse the suppression. In vitro treatment of anti-CD3-induced suppressor cells with either the OKT4 mAb plus complement or the OKT8 mAb plus complement partially decreased the suppression of proliferative responses of PBMC to PHA or allogeneic cells in mixed lymphocytes culture. However, treatment with both OKT4 and OKT8 mAb's plus complement or the OKT11 mAb plus complement completely abolished the suppression. These results suggest that the suppressor cells are of the T11+T4+T8- and T11+T4-T8+ phenotypes. In other experiments, T4+T8- and T8+T4- cells were isolated from PBMC treated for 48 hr with anti-CD3 mAbs. Both these two populations significantly inhibited proliferative responses of autologous PBMC to PHA and de novo immunoglobulin synthesis and secretion by mixtures of purified T4 and B cells from normal donors, in the PWM-induced differentiation system. These results demonstrate that anti-CD3-induced suppressor cells are of the T4 or T8 phenotype. Treatment of purified T4+T8- and T8+T4- cells with anti-CD3 mAb's resulted in the generation of suppressor cells, suggesting that the precursors of the anti-CD3-induced suppressor cells can belong to either of these two populations.(ABSTRACT TRUNCATED AT 400 WORDS)     

Deficiencies in suppressor T cell activity seen in patients with active systemic lupus erythematosus are due to the dilution of normally functioning suppressor T cells by nonsuppressor T cells

Concanavalin A (Con A)-activated T lymphocytes from patients with active, but not inactive, systemic lupus erythematosus (SLE) failed to express normal suppressor activity, regardless of the phenotype of CD4+ or CD8+. Con A-activated CD4+ or CD8+ T lymphocytes from the SLE patients and from normal controls were further separated into two populations, using the autologous erythrocyte rosette technique. One population very rich in cells capable of forming rosettes with autologous erythrocytes from the active patients showed the same degree of suppressor activity, as did that from normal controls; the CD4+ or CD8+ population poor in autorosetting cells derived from Con A-activated T lymphocytes from both the controls and patients did not express suppressor activity. Moreover, when autorosetting T cells from the active patients and nonrosetting cells from the same patients were mixed at a normal ratio (4:6), normal suppressor activity could be restored. It was notable that the frequency of autorosette-forming cells was markedly reduced in the Con A-activated T lymphocytes from the active, but not inactive, SLE patients, regardless of the phenotype of CD4+ or CD8+. These findings indicate the presence of a normally functioning suppressor T cell population in patients with active SLE. It seems that the lack of suppressor T cell function in patients with active SLE is due to the dilution of a few normal suppressor T cells by large numbers of nonsuppressor T lymphocytes.     

Proliferation of chicken peripheral blood leukocytes in response to pokeweed mitogen is macrophage dependent

Chicken peripheral blood leukocytes (PBL) proliferate in vitro in response to a wide range of pokeweed mitogen (PWM) concentrations. The PWM response was not influenced by the major histocompatibility complex (MHC) haplotype nor by the intrinsic responsiveness of the PBL to concanavalin A (Con A). The results indicate that PWM under our conditions stimulates B-lineage cells, although a T-cell subset is also clearly induced to division. The PBL from B-cell-depleted animals gave substantially lower responses than those from normal controls. Pokeweed mitogen stimulation of PBL was adherent cell dependent. Thus the low PWM response of adherent cell-depleted PBL was reconstituted by the addition of irradiated unseparated PBL. Furthermore, purified irradiated adherent cells containing greater than 90% macrophages were also able to reconstitute PWM responses. Finally, we have shown that PWM was able to induce large numbers of B cells to produce cytoplasmic immunoglobulin. However, only a minor proportion of such cells were induced to immunoglobulin secretion.     

A defect in the suppressor circuits among OKT4+ cell populations in patients with systemic lupus erythematosus occurs independently of a defect in the OKT8+ suppressor T cell function

The autologous mixed lymphocyte reaction (MLR) is thought to be part of a regulatory role of T cells on B cell function. OKT4+, but not OKT8+, cells can proliferate in response to autologous non-T cells. Moreover, the OKT4+ cell population activated early in the course of autologous MLR functioned as inducer cells for the differentiation of B cells, whereas later in the response, the activated OKT4+ cells were particularly enriched in suppressor cells. A part of the autologous MLR appears to be an important pathway for the activation of feedback suppression mechanisms among cells contained within the OKT4+ populations. Patients with systemic lupus erythematosus (SLE) were studied with regard to the following OKT4+ cell functions in vitro after activation in the autologous MLR: a) proliferative response, and b) helper and suppressor activities for differentiation of B cells. A marked reduction in the proliferative response of OKT4+ cells was observed in SLE patients. SLE OKT4+ cells activated in the autologous MLR could function as helper cells but could not exert any suppressor activity. This OKT4+ cell abnormality was present regardless of the disease activity, and occurred in the absence of autoantibodies including anti-T cell antibodies. Instead, SLE anti-T cell antibodies could preferentially eliminate cells bearing the OKT8+ phenotype characteristic of suppressor cells in populations of normal T cells. These results suggest that the defect in the suppressor circuits among OKT4+ cell populations is intrinsic to SLE lymphocytes and that the OKT8+ suppressor T cell defect is caused by antibodies produced by the B cells of SLE patients.     

Cytotoxic effector cell function in organized gut-associated lymphoid tissue (GALT).

Lymphocytes from the organized gut-associated lymphoid tissues (GALT) of adult guinea pigs were examined for surface markers characteristic of T and B lymphocytes and for their capacity to function as effector cells in mitogen-induced cellular cytotoxicity (MICC) and antibody-dependent cellular cytotoxicity (ADCC) reactions. GALT lymphocytes formed rosettes with rabbit erythrocytes, a T-cell marker, and underwent proliferative responses in vitro in the presence of phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM). GALT lymphocytes were cytotoxic in vitro for erythrocyte and DBA mastocytoma targets in the presence of PHA. A population of GALT lymphocytes bound aggregated γ-globulin; however, they functioned poorly in ADCC reactions. Thus, organized GALT in the guinea pig contains lymphocytes capable of functioning in T-cell-dependent MICC reactions but either lacks the effector cell population which mediates ADCC or contains an effector cell which functions poorly in ADCC.     

Effect of T- and B-lymphocyte mitogens on interactions between lymphocytes and macrophages.

The mitogenic response of murine T cells ² to Con A, S-Con A and PHA was found to be macrophage-dependent. Optimal mitogenic responses were obtained when macrophage-depleted T-cell populations were reconstituted with 5% normal peritoneal macro-phages. Studies were carried out to investigate the effect of T- and B-cell mitogens on in vitro physical interactions between murine lymphocytes and macrophages. This was done by determining the number of T- or B cells binding to macrophages in the absence and in the presence of T- and B cell mitogens, and comparing the results of these experiments with the induction of lymphocyte proliferation. Con A increased the binding of T cells to macrophages when used in mitogenic doses (1–5 μg/ml). Dose response experiments showed that the same dose of Con A which produced maximal mitogenic stimulation also induced the greatest number of T cells to bind to macrophages. Nonmitogenic doses of Con A (20–50 μg/ml) did not enhance the binding of T cells, while identical doses of S-Con A both induced T cell mitogenesis and increased the number of T cells bound to macrophages. Similar results were obtained with PHA. None of the B-cell mitogens tested (LPS, EPO 127 and LAgl) increased the binding of either T or B cells to macrophages. PWM, which is mitogenic for both T and B cells, increased the binding of T cells to macrophages, but not that of B cells. In brief, the four T-cell mitogens tested (Con A, S-Con A, PHA, and PWM) induced specific physical interactions between T cells and macrophages, while none of the B-cell mitogens had any effect on the physical interactions between either B or T cells and macrophages when used in mitogenic doses.     

Identification of the T cell subset that produces human gamma interferon

Positive and negative selection procedures combined with cytofluorographic analysis and lysis with monoclonal antibodies were utilized to identify the T lymphocyte subset that produces human gamma interferon (gamma-IFN) (formerly referred to as "immune" or "type II" interferon) in response to mitogen stimulation. Lymphocytes were separated on the basis of their Fc receptors for IgG or IgM, their nonreactivity with IgM or IgG antibodies, and their reactivity with the monoclonal antibodies OKT4, OKT8, OKT11a, and OKM1. Isolated T cell subsets were incubated with the gamma-IFN inducer, phytohemagglutinin. Three days after induction, the cell supernatants were harvested and assayed for interferon. The T cell subset that produces gamma-IFN was identified as E rosette positive with the phenotype: T gamma, T non-micro, OKM1+, OKT4-, OKT8- and OKT11a+. gamma-IFN production by cells was resistant to doses of x-irradiation that abrogate mitogen-induced T suppressor function but was highly sensitive to low doses of 4-hydroperoxycyclophosphamide. These data demonstrate that gamma-IFN is produced by the T gamma, OKM1+ lymphocyte subset, but these cells may also require the presence of accessory monocytes for elaboration of gamma-IFN. The anti-proliferative activity of gamma-IFN may be responsible for the previously described suppressor function of this subset, and gamma-IFN production by T gamma cells may distinguish this subset from the suppressor/cytotoxic functions of the OKT8+ subset or the mitogen-induced OKT4+ suppressor.     

Immunoregulation in experimental filariasis. I. In vitro suppression of mitogen-induced blastogenesis by adherent cells from Jirds chronically infected with Brugia pahangi

Nonspecific immunoregulatory events were examined in inbred jirds chronically infected with Brugia pahangi. The responsiveness of spleen cells from infected animals to the T cell mitogens PHA and Con A and to the B cell mitogens, LPS and PWM, was found to be suppressed by as much as 90% when compared with the reactivity of lymphocytes from normal animals. Furthermore, spleen cells from infected jirds were capable of suppressing the mitogen reactivity of normal spleen cells. Depletion of cells adherent to nylon wool, glass wool, or plastic alleviated the regulatory activity exerted by spleen cells from infected jirds. Addition of indomethacin, an inhibitor of prostaglandin synthetase, to cultures of spleen cells from infected animals did not alter the suppression observed. In contrast, lymphocytes from the peripheral lymph nodes of infected jirds did not exhibit depressed T cell mitogen reactivity and were incapable of suppressing the PHA or Con A responsiveness of normal lymph node cells. However, the reactivity of lymph node cells from infected jirds to B cell mitogens, LPS and PWM, was suppressed. These results imply the existence of multiple regulatory mechanisms, at least one of which is restricted to the spleen. The relevance of nonspecific regulation to development of parasite-specific immunologic reactivity and to the infection is discussed.     

A feline thymocyte antigen defined by a monoclonal antibody (FT2) identifies a subpopulation of non-helper cells capable of specific cytotoxicity

A monoclonal antibody, FT2 (IgG1 kappa) prepared against cat thymocytes, was found to be reactive with an antigenic determinant expressed by approximately 76% of thymocytes, 15% of blood mononuclear cells, 14% of splenocytes, and 1% of bone marrow cells. The FT2-reactive determinant was not expressed on B cells, macrophages, granulocytes, or erythrocytes. Both FT2+ and FT2- populations of peripheral blood mononuclear cells were capable of proliferative responses to the T cell mitogens Con A and PHA. When splenocytes were sensitized to the lymphoblastoid cell line, 79p90, cytotoxic T cells were found in the FT2+ population and were absent from the FT2- population. Conversely, the FT2- population contained the helper T cell activity required for pokeweed mitogen-induced B cell differentiation. Under nonreducing conditions, the FT2 antigen had an apparent m.w. of 71,000. When reduced, subunits of 31,000 and 38,000 apparent m.w. were observed. The data suggest that the FT2 antibody identifies the feline analog of the human T8/Leu-2, murine Ly-2 molecules expressed by cytotoxic/suppressor T cells.     

Immunomodulatory role of thyroid hormones: in vitro effect of tetraiodothyronine (T4) on mitogen induced blastogenic response of lymphocytes

An attempt was made to find out the immunomodulatory role of thyroid hormone, tetraiodothyronine (T4), and its effect on in vitro mitogen induced blastogenesis. Human peripheral blood lymphocytes (PBL) were subjected to phytohaemagglutinin (PHA) concanavalin-A (Con. A) and pokeweed mitogen (PWM) in presence or absence of T4. Basal blastogenic response was significantly enhanced in dose related manner by T4. PHA and Con.A induced response was depressed significantly (r = -0.975 and r = -0.945) whereas less than 50 ng T4 in presence of PHA showed mild stimulation. On the other hand, PWM induced response in presence of T4 was enhanced significantly in dose related manner.     

Polysaccharides with sulfate groups are human T-cell mitogens and murine polyclonal B-cell activators (PBAs). I. Fucoidan and heparin

We reported previously that dextran sulfate and carrageenan (kappa, lambda, and iota), which are sulfated polysaccharides, were human T-cell mitogens and mouse polyclonal B-cell activators (PBA). To clarify our working hypothesis further, we used fucoidan and heparin, both sulfated polysaccharides. The following results were obtained: (1) fucoidan is human T-cell mitogen and a mouse PBA; (2) heparin is also a human T-cell mitogen and a mouse PBA, but the degree of the responses by heparin is lower than that by fucoidan; (3) helper T-cell-dependent B-cell differentiation was not observed, since both fucoidan and heparin activate OKT4⁺ cells and OKT8⁺ cells nonspecifically and suppressor T cells (OKT8⁺ cells) may inhibit the helper function of B-cell differentiation by helper T cells (OKT4⁺ cells); and (4) our working hypothesis that polysaccharides with sulfate groups are human T-cell mitogens and mouse PBAs was further strengthened. The relationship between molecular weight and sulfate groups of the polysaccharides is discussed in detail.     

Differential effects of concanavalin A and phytohemagglutinin on murine immunity. Suppression and enhancement of cell-mediated immunity.

To assess the effects of the selective T-cell mitogens concanavalin A (Con A) and phytohemagglutinin P (PHA) on cell-mediated immunity (CMI), the mitogens were injected before, with, or after intravenous (iv) challenge of mice with Listeria monocytogenes. Mitogenic treatment differentially influenced the CMI response to Listeria. Con A enhanced listericidal activity when given before or with Listeria challenge, but Con A suppressed the CMI response when given after infection with Listeria. In contrast, PHA enhanced listericidal activity at all intervals. Since Con A, but not PHA, affected the growth of Listeria in the spleens of mice 24 and 48 hr after infection, Con A was shown to have an immediate effect on the development of listericidal activity and PHA was shown to have a delayed effect. In addition, Con A induction of immediate nonspecific listericidal activity was short-lived, while PHA induced a longer-lasting effect on resistance to Listeria. The mitogen-induced effects in the CMI response to Listeria were shown to be dependent upon the activities of activated T cells. The enhancement and suppression of listericidal activity appears to result from the activation of different T-cell subpopulations, known to be stimulated preferentially by Con A or PHA.     

The anti-T cell monoclonal antibody 9.3 (anti-CD28) provides a helper signal and bypasses the need for accessory cells in T cell activation with immobilized anti-CD3 and mitogens

CD28 is an antigen of 44 kDa which is expressed on the membrane of the majority of human T cells. The present study examines the functional effects of an anti-CD28 monoclonal antibody (mAb 9.3) on T cell activation induced with immobilized anti-CD3 mAb OKT3 or with mitogens, in the absence of accessory cells. To this end, we used blood resting T cells that were completely depleted of accessory cells (monocytes, B cells, and natural killer cells), and consequently did not respond to recombinant interleukin-2 (rIL-2), to immobilized OKT3, to PHA, or to Con A. Addition of mAb 9.3 to the cultures enhanced IL-2 receptor expression (Tac antigen) on PHA- or immobilized OKT3-stimulated T cells and induced IL-2 receptors on Con A-stimulated T cells. Moreover, addition of mAb 9.3 to cultures of T cells stimulated with PHA, Con A, or immobilized OKT3 resulted in IL-2 production. Soluble mAb 9.3 was a sufficient helper signal for T cell proliferation in response to PHA or immobilized OKT3. Crosslinking of mAb 9.3 by culture on anti-mouse IgG-coated plates enhanced the helper effect and was an essential requirement for the induction of T cell proliferation in response to Con A. No other anti-T cell mAb (anti-CD2, -CD4, -CD5, -CD7, -CD8) was found to provide a complete accessory signal for PHA or Con A stimulation of purified T cells. T cell proliferation induced by the combination of PHA and mAb 9.3 was strongly inhibited by the anti-IL-2 receptor mAb anti-Tac. In conclusion, mAb 9.3 can provide a signal bypassing monocyte requirement in T cell activation with immobilized OKT3, PHA, and Con A, resulting in an autocrine IL-2-dependent pathway of proliferation.     

In vitro effects of retinoids on murine thymus-dependent and thymus-independent mitogenesis

The effects of three retinoids: all-trans-retinoic acid (RA), 13-cis-retinoic acid (13-cis-RA), and N-(4-hydroxyphenyl)retinamide (4-HPR) on murine splenic lymphocyte proliferative responses to mitogens were evaluated. The responses to T-cell mitogens, PHA and Con A, and a T-cell-dependent B-cell mitogen, PWM were significantly potentiated by these retinoids. However proliferative responses to a B-cell mitogen, Escherichia coli LPS were unaffected or inhibited. All three retinoids at concentrations ranging from 10(-6) to 10(-15) M significantly potentiated Con A-induced proliferative responses. In response to PWM, 10(-13) M RA, 10(-12) M 13-cis RA, and 10(-11) M 4-HPR were the lowest concentrations producing significant potentiation. Endpoint concentrations of retinoids significantly potentiating responses to PHA were; 10(-9) M RA, 10(-8) M 13-cis RA, and 10(-6) M 4-HPR. These responses were independent of retinol contained in fetal calf serum supplemented medium since responses were reproduced in serum-free medium devoid of retinol. Optimal potentiation by retinoids of responses to these T-cell-dependent mitogens were found at superoptimal concentrations of mitogen suggesting a selective inhibition of T-suppressor cells. Thus, potentiation of T-cell-dependent mitogen responses provides the most sensitive biological assay yet described for detection of retinoid activity and is a reproducible system to explore the cellular and molecular mechanisms of retinoid-mediated immunopotentiation.     

Pokeweed mitogen-induced immunoglobulin secretion by peripheral blood lymphocytes from patients with primary intracranial tumors. Characterization of T helper and B cell function

We have previously demonstrated that patients with primary malignant brain tumors have impaired in vivo and in vitro cell-mediated immunity. The purpose of the present research was to employ pokeweed mitogen (PWM)-induced secretion of immunoglobulin (Ig) by peripheral blood lymphocytes (PBL) to further investigate impaired lymphocyte function in these patients. The PWM response of PBL from normal individuals averaged 8384 plaque-forming cells (PFC) per 10(6) cells, whereas the response of PBL from patients averaged 1590 PFC/10(6). The decreased PWM response of PBL patients could not be improved by varying the number of PBL placed in culture or employing different concentrations of PWM. Co-culture experiments to detect the presence of suppressor cells in PBL and purified T cell preparations from patients demonstrated that enhanced suppressor cell activity was not evident. Next, experiments were performed to assess the T-helper cell activity present in purified T cell preparations obtained from patients. The results demonstrated that T cells from patients lacked the ability to provide adequate helper activity in the PWM response. Moreover, studies with monoclonal antibodies directed against T cell subsets revealed that PBL from patients have a reduced percentage of T-helper cells (40%) as compared with normal values (55%). In concert with T-helper cell anomalies, B cell function in these patients also is diminished. Thus, these observations indicate that a combined T-helper and B cell defect may contribute to the broad impairment of host immunocompetence observed in patients with primary gliomas.