Activation of lymphokine genes during stimulation of cloned T cells

To study the regulation of lymphokine production by T lymphocytes, we have characterized the activation of lymphokine genes in T cells by measuring the levels of lymphokine mRNA in cloned murine T lymphocytes after stimulation. Lymphokine mRNA was not detected in cells taken after seven days of maintenance culture. Following stimulation of T helper lymphocytes L2 and AD9.1 with concanavalin A, lymphokine mRNA appeared, reached peak levels and disappeared over a 43-h time period. A single stimulation event resulted in the induction of mRNA for interleukin 2 (IL 2), IL 3 and interferon gamma. Maximal mRNA levels were generally found at 6 h in the T helper lymphocytes, but could occur as late as 18 h. The lymphokine genes were expressed coordinately; however, in these cloned cells, IL 2 mRNA levels appeared to be lower than the other two mRNAs. Lymphokine titers in the supernatant fluids paralleled the appearance of mRNA but IL 2 titers began to fall after 12 h probably because of utilization of this lymphokine by the activated cells. In the cytolytic T lymphocyte, L3, qualitatively similar kinetics were found after stimulation by lectin or a clonotypic antibody with peak mRNA levels occurring later (18 h) with the antibody. These studies indicate a single stimulating event activates the lymphokine genes of T cells in a coordinate manner; the appearance of the lymphokines in supernatant fluids represents de novo synthesis of these proteins but the levels of lymphokines measured in supernatant fluids reflects both production and utilization rates, and exposure to IL 2 at the time of stimulation is not essential for the production of other lymphokines.     

Characterization of the suppressor activity in lymphocytes from patients with common variable hypogammaglobulinemia: evidence for an associated primary B-cell defect

The pathogenetic mechanisms responsible for the impaired immunoglobulin production in common variable hypogammaglobulinemia (CVH) are diverse with abnormalities in both B cells and immunoregulatory T cells. Production of IgG, IgM, and IgM-rheumatoid factor (IgM-RF) was measured in pokeweed mitogen (PWM) or Epstein-Barr virus (EBV)-stimulated cultures using various combinations of CVH, cord blood mononuclear cells (CBMC), and normal adult control B and T cells. The following results were obtained. First, the proportion of OKT3+ and OKT8+ cells were increased in CVH patients. Second, the T cells from four CVH patients and CBMC suppressed PWM-induced IgG, IgM, and IgM-RF production by normal B cells. Furthermore, major suppressor activity was found in the OKT8+ T-cell subpopulations in CBMC and three out of four CVH patients. There was no significant difference in relative suppression by OKT8+ cells from normal adults, CVH patients, or CBMC. However, in one CVH patient suppressor T cells were found in both OKT4+ as well as OKT8+ fractions. In the CVH patient with OKT4+ suppressor cells, X irradiation (1250 rads) abrogated suppressor activity and restored helper activity in the OKT4+ T-cell fraction. Irradiation of normal OKT4+ cells did not increase helper activity. When non-E-rosetting cells from normal subjects, CVH, and CBMC were stimulated with EBV it was observed that normal adult B cells could be induced to secrete IgG, IgM, and Ig-RF whereas CVH and CBMC could only produce IgM and IgM-RF but not IgG. The present study demonstrates for the first time that a radiosensitive OKT4+ suppressor cell is present in some CVH patients.     

Defective DNA synthesis by T cells in acquired ''common-variable'' hypogammaglobulinaemia on stimulation with mitogens.

We have studied T cell defects in acquired 'common-variable' hypogammaglobulinaemia (CVH) by measuring the synthesis of DNA, RNA and protein in vitro in response to mitogens and to interleukin 2 (IL-2). We have confirmed that some patients have defective DNA synthesis in response to PHA and shown that this extends to responses to cell-derived B cell growth factor (c-BCGF) which is also mitogenic to T cells. DNA synthesis induced by IL-2 was not defective in these patients suggesting IL2-receptor induction is normal. The mitogen-related defect in DNA synthesis was not accompanied by any reduction in synthesis of RNA or of protein. Levels of the rate limiting enzyme (thymidylate synthetase EC 2.1.1.45) responsible for de novo DNA synthesis in the absence of endogenous thymidine were measured following PHA stimulation and found to be in the normal range. In the CVH patients (but not in normal individuals) the relationship between the levels of thymidylate synthetase and DNA synthesis in response to PHA approached significance, suggesting that this pathway becomes more important in CVH patients than in normal individuals perhaps because of defects in the thymidine 'salvage' pathway.     

Reduced interleukin-2 (IL-2) production in common variable immunodeficiency is due to a primary abnormality of CD4+ T cell differentiation

Common variable immunodeficiency (CVI) is a condition characterized by hypogammaglobulinemia and impaired antibody responses, resulting in recurrent bacterial infections in untreated patients. In addition, affected individuals exhibit an increased incidence of autoimmunity, malignancy, and certain viral infections, suggesting the presence of an underlying generalized immune dysregulation. We have previously described a subgroup of CVI patients in whom T cells within PBMC populations exhibit a selective defect in lymphokine production. IL-2, IL-4, and IL-5 mRNA production was impaired in these patients, while proliferation, IL-2R expression, and c-myc mRNA production were normal. In the present series of experiments, using highly purified CD4+ T cells prepared by negative selection, we show that this lymphokine production defect is a primary abnormality of CVI CD4+ T cells: whereas CD4+ T cells from CVI patients proliferate normally in response to stimulation by PHA, staphylococcal enterotoxin B (SEB), or anti-CD2 antibodies, these stimuli induce significantly less IL-2 production than observed with CD4+ T cells from normal individuals. Furthermore, we show that this IL-2 production defect is not due to an accessory cell abnormality, since it was seen in the presence of normal (allogeneic) accessory cells, and patient accessory cells supported normal amounts of IL-2 production by PHA-stimulated CD4+ T cells obtained from normal individuals. Of interest, we also found that while IL-2 production by CD4+ T cells from CVI patients induced by stimulation with immobilized anti-CD3 antibody was reduced compared to CD4+ T cells from normal control individuals, this reduction was not statistically significant. Furthermore, stimulation of both CVI patient and normal CD4+ T cells with either ionomycin + phorbol myristate acetate or a combination of immobilized anti-CD3 antibody plus anti-CD28 antibody resulted in a 50-fold increase in IL-2 production compared to stimulation with immobilized anti-CD3 antibody alone, and, under these conditions, CVI and normal CD4+ T cells produced equivalent amounts of IL-2. Finally, minor defects in interferon- production by CD4+ T cells from CVI donors were observed, but these were less severe than the IL-2 production defects and were not statistically significant. We conclude that a primary abnormality of lymphokine production exists in the CD4+ T cells of a subset of patients with CVI. The fact that the IL-2 production defect is more severe upon stimulation with superantigen as opposed to anti-CD3 antibody, and could be overcome by stimulation with ionomycin + phorbol myristate acetate or by costimulation with immobilized anti-CD3+ anti-CD28 antibodies, implies that this defect is due to impairment of a specific signaling pathway.     

Signaling via major histocompatibility complex class II molecules and antigen receptors enhances the B cell response to gp39/CD40 ligand

Activated T cells induce proliferation and differentiation of resting B cells in vitro through their CD40 molecules and lymphokine receptors. However, despite constitutive B cell expression of CD40 and lymphokine receptors, widespread nonspecific polyclonal B cell activation by activated T cells is seldom observed in vivo. The present study was designed to test the hypothesis that signals delivered via the B cell antigen (Ag) receptor (membrane immunoglobulin, mIg) and major histocompatibility complex (MHC) class II molecules enhance B cell responsiveness to CD40-mediated signals, providing specificity to the Ag-nonspecific, MHC-unrestricted CD40 signal. To test this hypothesis, both an Ag-specific mouse B cell clone CH12.LX, and freshly isolated resting splenic B cells were cultured with either soluble or membrane-bound forms of the T cell ligand for CD40 (CD40L), in the presence or absence of additional signals provided by Ag or anti-IgM, interleukin-4, and class II-specific monoclonal antibody (mAb). Differentiation of CH12.LX cells and proliferation of splenic B cells in response to both forms of CD40L was greatly enhanced by exposure to mIg-mediated signals, with greatest enhancement seen when cells were cultured with Ag prior to receiving other signals. Response to CD40L was further enhanced by concurrent culture with class II-specific, but not class I-specific mAb. Enhancement was greatest at limiting concentrations of CD40L. The ability of class II MHC-mediated signals to enhance Ag-specific B cell responsiveness to CD40-mediated signaling may selectively promote the activation of B cell clones capable of cognate interactions with helper T cells.     

IL-6协同PHA对静止T淋巴细胞增殖的影响

本文研究了IL-6协同PHA对静止T淋巴细胞增殖的影响。PHA单独不能刺激处于静止期的T淋巴细胞发生增殖反应,但联合IL-6后能引起静止T淋巴细胞发生明显的增殖反应。此增殖反应不为抗IL-2aR的单克隆抗体anti-Tac所抑制,却被免疫抑制剂Cyclosporin A(CsA)所阻断,Cs A能抑制T淋巴细胞内同Ca~(2+)有关的信号传递以及后续的淋巴因子mRNA的表达。这表明在IL-6对T淋巴细胞的作用过程中,有一个Ca~(2+)参与的信号传递以及某种淋巴因子mRNA表达的过程。提示IL-6可能是通过诱导其它的生长因子的产生而作用于T淋巴细胞,而且这条作用途径可能是独立于传统的IL-2途径的。     

Mutual Antagonism Between Antigen-and Lipopolysaccharide-Induced Antibody Production

B cells are induced to antibody production by antigens or by mitogens, such as lipopolysaccharide (LPS). We observed a mutually antagonistic relationship between activation through the antigen-receptor (AgR) and LPS-receptor (LPSR) in vitro. Prior exposure of B cells to AgR-ligating antibody prevented antibody forming cell (AFC) production induced by LPS, but not that induced by specific antigen (SRBC, TNP-Ficoll, or TNP-LPS). AFC production induced by antigen could be abrogated by concomitant exposure to LPS; the shutdown of the antigen-driven response was apparent when LPS-induced AFC were prevented by pre-exposure to antibody against the AgR. The ability of signaling through the AgR to inhibit antibody production stimulated by LPS was seen in DBA/2 and BALB/c mouse strains, and not in the New Zealand Black (NZB) strain. The results suggest that mutual antagonism is distinct from other forms of immune hyporesponsiveness, and that defects in antagonism may be a factor in the development of autoimmune disease.     

Mutual Antagonism Between Antigen-and Lipopolysaccharide-Induced Antibody Production

B cells are induced to antibody production by antigens or by mitogens, such as lipopolysaccharide (LPS). We observed a mutually antagonistic relationship between activation through the antigen-receptor (AgR) and LPS-receptor (LPSR) in vitro. Prior exposure of B cells to AgR-ligating antibody prevented antibody forming cell (AFC) production induced by LPS, but not that induced by specific antigen (SRBC, TNP-Ficoll, or TNP-LPS). AFC production induced by antigen could be abrogated by concomitant exposure to LPS; the shutdown of the antigen-driven response was apparent when LPS-induced AFC were prevented by pre-exposure to antibody against the AgR. The ability of signaling through the AgR to inhibit antibody production stimulated by LPS was seen in DBA/2 and BALB/c mouse strains, and not in the New Zealand Black (NZB) strain. The results suggest that mutual antagonism is distinct from other forms of immune hyporesponsiveness, and that defects in antagonism may be a factor in the development of autoimmune disease.     

Differential effects of the immunosuppressive macrolides FK-506 and rapamycin on activation-induced T-cell apoptosis.

Activation of certain T-cell lines induces, besides lymphokine production, a suicide process (apoptosis) mediated by fragmentation of the cell's genome. This also occurs intrathymically during negative selection of the T-cell receptor (TcR) repertoire. Cyclosporin A (CsA) has been shown to block activation-driven T-cell apoptosis, an effect which may account for the perturbations of TcR repertoire selection caused by this agent in vivo. Recently, the macrolide FK-506 was demonstrated to suppress T-cell activation by inhibiting lymphokine production in a manner apparently similar to CsA. Thus, it seemed important to determine whether FK-506 would also prevent T-cell apoptosis. For the purpose of comparison, we also investigated rapamycin (RAP), a macrolide structurally related to FK-506, but that does not block lymphokine production and antagonizes the immunosuppressive action of FK-506. The DO-11.10 T-cell hybridoma stimulated with ionomycin plus PMA was used as a model system. FK-506 (1.2 nM) totally prevented DNA fragmentation detectable by agarose gel electrophoresis at 16 h of culture. FK-506 still inhibited this phenomenon when added 2 h after the initiation of the cultures but not later. In contrast, concentrations of RAP as high as 1 microM failed to block apoptosis. However, RAP (110 nM) reversed the apoptosis-inhibitory effect of FK-506, even if added 1-2 h after the latter to the cultures. Consistent with this antagonism, RAP also reversed the binding of a radiolabeled derivative of FK-506 in DO-11.10 cells. Therefore, FK-506 interferes with an early event of T-cell activation that leads to apoptosis whereas RAP does not.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of L3T4+ cells in the pathogenesis of lupus in lpr-bearing mice. I. Defects in the production of interleukins 2 and 3

Mice which bear the lpr gene spontaneously develop autoimmune syndromes characterized by massive expansion of an unusual T cell subset which is phenotypically Thy-1+, L3T4-, Lyt-2-, B220+. The mutant T cells are refractory to stimulation with mitogenic lectins and, by implication, are thought to be solely responsible for the defects in lymphokine production manifested by lpr mice. The contribution of the remaining L3T4+ T cell subset to the latter derangements has not been previously examined and is the focus of this study. We found that abnormalities in concanavalin A-induced interleukin 2 and 3 production in the spleens of MRL-lpr/lpr and C57BL/6.lpr mice occurred in the presence of limited infiltration with B220+, L3T4- T cells. Mixing experiments indicated that B220+ T cells were not suppressive. Furthermore, lpr spleen cells enriched for L3T4+ cells and depleted of sIg+, B220+ and Lyt-2+ cells demonstrated reductions in lymphokine production which were comparable to those seen in unfractionated preparations. Spleen cells from C57BL/6.lpr mice, enriched for L3T4+ cells, were also markedly impaired in a mixed leukocyte reaction in response to stimulator cells from the class II major histocompatibility complex mutant bm12. The results indicate that the aberrations in lymphokine production and proliferation in the spleen cells of lpr mice involve not only B220+ T cells but also L3T4+ cells and suggest a potential role for the L3T4+ subset in the pathogenesis of lupus in lpr-bearing mice.     

Inhibition of B cell growth factor (BCGF) by monoclonal antibodies directed against the C3d receptor (CR2)

Normal human B cell proliferation is controlled by various immunoregulatory signals including the T cell-derived lymphokine B cell growth factor (BCGF). Human BCGF provides the final proliferative signal to normal, activated B cells. We herein show that anti-CR2 monoclonal antibodies inhibit human B cell responsiveness to purified BCGF. Addition of anti-CR2 antibody, AB5, was capable of completely inhibiting BCGF-mediated enhancement of either anti-mu or staphylococcal protein A-activated human B cells (191 +/- 21 cpm vs. 3942 +/- 622 cpm, mean +/- SEM). Inhibition of B cell response to BCGF by AB5 occurred in a dose-dependent manner. Monoclonal antibody anti-B2, which recognizes the same 140-kDa glycoprotein as AB5, in comparable concentrations also inhibited B cell responsiveness to BCGF. Monoclonal antibodies of the same subclass (IgG1) showed no inhibitory effect on BCGF enhancement of B cell proliferation. The F(ab')2 fragment of AB5 generated by pepsin digestion was similarly inhibitory as was the intact Ig. AB5-mediated inhibition was independent of the target B cell state of activation. Both resting and activated B cells (anti-mu or staphylococcal protein A activated) incubated with similar concentrations of AB5 were unresponsive to BCGF. The ability of anti-CR2 antibodies to block BCGF-dependent B cell proliferation suggests that occupancy of C3d membrane receptors may result in modulation of B cell proliferation in physiologic or clinical disease states.     

B-T cell interactions modulate inhibitory effects of interleukin-4 on human B cell proliferation

In this study, we investigated the role of B-T cell contacts in interleukin Ia-mediated inhibition of human B lymphocyte proliferation induced by mitogenic doses of soluble anti-μ monoclonal antibody (mAb). We show that additional cross-linking of B cell antigens, using Sepharose beads coated with anti-μ, anti-(IL)-4 mAb (but not soluble mAb) or anti-CD40 antigen counteracted the inhibitory activity of IL-4. More importantly, cell contacts between B cells and activated T cells (but not unstimulated T cells) were sufficient to counteract IL-4-mediated inhibition of DNA synthesis. In addition, the inhibitory activity of IL-4 on chronic lymphocytic leukemia B cells stimulated with anti-μ and IL-2 was itself reduced by the presence of fixed activated T cells. Our data suggest that a major role for IL-4 would be to prepare B cells to receive additional mitogenic signals through cell contact interactions with activated T lymphocytes. When such interactions do not occur IL-4 may block DNA synthesis, preventing uncontrolled B cell proliferation.     

Lymphokine-mediated fusion and migration inhibition of alveolar macrophages

Guinea pigs were shown to produce a lymphokine termed macrophage fusion factor (MFF) which mediated the fusion of 70–80% of guinea pig or rabbit alveolar macrophages, but not guinea pig peritoneal macrophages. In the conventional migration inhibitory factor (MIF) assay, guinea pig aveolar macrophages were inhibited in their migration and large numbers of giant cells were present. There appeared to be a correlation between the titer of MFF and migration inhibition of alveolar macrophages but not with MIF titer as expressed on the peritoneal macrophage. Guinea pig MFF production was erratic and its absence from lymphokine supernatant fluids correlated with an absence of migration inhibitory activity for the alveolar macrophage. Guinea pig MIF production was more constant and high titers were invariably present. Rabbit crude lymphokine supernatant fluids containing MFF also inhibited the migration of their alveolar macrophages when measured at 24 and 48 hr during the MIF assay. Extensive numbers of giant cells were observed in the cell fan whenever migration inhibition was present. α-l-Fucose, which is known to block the receptor sites of MIF, failed to block giant cell formation in either the MFF or the MIF assay and also failed to block migration inhibition of the alveolar macrophages. The results suggest that lymphokines other than MIF can inhibit the migration of alveolar macrophages in the standard MIF assay and that the lymphokine responsible for migration inhibition and fusion of alveolar macrophages is the same lymphokine, MFF.     

Human interleukin-5 induces staphylococcal A Cowan 1 strain-activated human B cells to secrete IgM

Studies on the role of human interleukin (IL)-5 in B cell growth and differentiation have yielded conflicting results. To clarify this issue, we studied the role of purified recombinant IL-5 on activated human B cells which were depleted of Tcells and adherent cells. Human IL-5 augments IgM secretion, but not IgG or IgA secretion of purified human B cells activated with staphylococcal A Cowan 1 strain (SAC). However, the period of B cell activation with SAC is critical for the B cell to respond to IL-5. After 24 h of SAC activation, human B cells are responsive to the IL-5 signal, but with longer periods of activation, IL-5 responsiveness diminishes. This may explain some of the previous conflicting results. The IgM enhancement was not seen when B cells were activated with pokeweed mitogen. In addition, human recombinant IL-4 synergized with IL-5 in augmenting IgM secretion by SAC-activated B cells, while IL-5 synergized with IL-2 to augment IgM, IgG and IgA secretion by SAC-activated B cells. As the purified IL-5 was derived from a COS-1 cell supernatant, and COS-1 cells secrete IL-6, we examined whether a polyclonal IL-6 antibody blocked the IgM-enhancing activity of IL-5. IL-6 antibody did not block the IL-5 enhancement of IgM secretion, but a monoclonal antibody to IL-5 inhibited the human IL-5 activity on human B cells. These results demonstrate that human IL-5 augments IgM secretion of SAC-activated human B-cells. In addition, this lymphokine synergizes with IL-4 and IL-2 in supporting Ig secretion.     

A monoclonal antibody inhibiting leucocyte adhesion blocks induction of IL-2 production but not IL-2 receptor expression.

Monoclonal antibody 60.3 defines the leucocyte antigen CD 18 and recognizes a cell surface glycoprotein with an apparent molecular weight (MW) of 90,000 expressed by most human peripheral blood and bone marrow cells. This antibody can, among other things, block phorbol ester-induced adhesion among human mononuclear leucocytes. We show in this study that phorbol esters alone can induce peripheral blood mononuclear cells (PBL) to secrete interleukin-2 (IL-2) and that the IL-2-dependent cell line CTLL can be used for measuring this lymphokine without influence of the phorbol esters themselves. These findings make it possible to analyse the capacity of antibody 60.3 to interfere with IL-2 production and receptor expression by phorbol ester or phytohaemagglutinin (PHA)-treated human PBL. A significant positive correlation between blockage of induced cell aggregation by antibody 60.3 and reduction in IL-2 release was observed. The addition of interleukin-1 (IL-1) restored IL-2 secretion in PHA-treated, but not in 4-beta-phorbol 12, 13-dibutyrate [P(Bu)2]-treated, cells in the presence of this antibody. In parallel, IL-2 receptor expression was determined by immunofluorescence using biotinylated anti-IL-2 receptor (Tac) antibodies. FACS analysis showed that IL-2 receptor expression was unaffected by antibody 60.3, whereas DNA synthesis of the same P(Bu)2-treated PBL was inhibited. However, addition of external recombinant IL-2 overcame this proliferation blockade. These results indicate that a cell-to-cell adhesion step is necessary for the production of IL-2, but not for the expression of its receptor on both PHA- and P(Bu)2-treated human PBL.     

Defect of T helper lymphocytes, as identified by the 5/9 monoclonal antibody, in patients with common variable hypogammaglobulinaemia.

Peripheral blood lymphocytes from 17 patients with common variable hypogammaglobulinaemia (CVH) were tested for reactivity with the 5/9 monoclonal antibody which reacts with about 15% of normal T-PBL in which all helper activity is found. In PBL from CVH patients, the proportions of OKT4 and OKT8 positive cells were also determined. Five patients had normal percentages of 5/9 cells and a normal OKT4/OKT8 ratio. Twelve patients had significantly decreased (or absent) 5/9 lymphocytes. Among these, five had decreased 5/9 cells and a normal OKT4/OKT8 ratio and seven had decreased 5/9 cells and an inversion of the OKT4/OKT8 ratio. The deficiency of the helper phenotype T cell subpopulation identified by the 5/9 monoclonal antibody in many patients with CVH may be relevant in the pathogenesis of this disease.     

Endogenous interleukin 6 plays an obligatory role in interleukin 4-dependent human IgE synthesis

The lymphokine interleukin (IL) 4 plays a crucial role in the regulation of IgE synthesis. In the present study, the cellular and cytokine requirements for the IL4-dependent induction of IgE synthesis in humans were analyzed. Recombinant IL4 could induce IgE synthesis by peripheral blood mononuclear cells and autologous T/B cell mixtures, but not by highly purified B cells. IgE induction by IL4 was strongly decreased in monocyte-depleted peripheral blood mononuclear cells. These results show that the induction of IgE synthesis by recombinant IL4 is T cell dependent and optimal in the presence of monocytes. IL5 and IL6, but not IL2, IL1 and tumor necrosis factor-alpha, strongly up-regulated the IL4-dependent synthesis of IgE, with modest effects on cell proliferation. An anti-IL6 polyclonal antibody strongly inhibited IL4-driven IgE production. Endogenous IL6 plays, therefore, an obligatory role in the IL4-dependent induction of IgE. However, a combination of IL4, IL5 and IL6 (with or without IL1) at optimal concentrations could not induce IgE synthesis by purified normal B cells, indicating that cytokine-mediated signals, although essential, are not sufficient for the IL4-dependent induction of IgE synthesis.     

A novel lymphokine derived from human IgG Fc receptor-bearing B cells: its suppressive effect on activated T and B lymphocytes including tumour cells in vitro.

Peripheral blood FcR gamma-bearing human B cells, but neither T cells nor adherent cells, produce an immunoregulatory lymphokine after receiving the stimulation of FcR gamma by immune complexes--antibody-sensitized erythrocytes (EA). This factor suppresses polyclonal immunoglobulin (Ig) production of B cells to pokeweed mitogen (PWM) and Nocardia opaca delipidated cell mitogen (NDCM), indicating that not only B cells, but also T cells are targets for this factor. It also inhibits the proliferation of mitogen-activated mononuclear and T and B tumour cells in vitro. The inhibitory effect on tumour cell growth is cytostatic, but not cytotoxic as in the case of lymphotoxin (LT). All these suppressive effects are observed in a HLA-non-restricted manner. Irradiation (2000 rads) of FcR gamma + B cells does not inhibit the production of this suppressive factor, implying that DNA synthesis is unnecessary. Nonstimulated FcR gamma + B cells retain the precursor activity for Ig-forming cells, since mononuclear cells untreated with EA respond to the mitogens, resulting in Ig production. However, it is worthy to note that they lose the activity when stimulated with immune complexes. Thus, the property obtained from human FcR gamma + B cells is similar to, but distinct from, a murine suppressive B-cell factor (SBF) prepared by the same procedure as for the human factor. Nevertheless, the observation in the present studies on the human analogue to murine SBF suggests that this factor, tentatively termed human SBF, appears to be a novel lymphokine which is different from any other factors, including LT, and that FcR-bearing B cells play an important role in the immunoregulatory mechanism in humans, as in the case of mice.     

The costimulatory signal CD28 is fully functional but cannot correct the impaired antigen response in T cells of patients with common variable immunodeficiency.

A wide spectrum of different immunologic abnormalities have been postulated as being responsible for the impairment of specific antibody production and the decrease in all or selected immunoglobulin isotypes present in common variable immunodeficiency (CVID). These abnormalities include impaired B cell differentiation and/or function, defective macrophage function, and significant T cell defects. The aim of the present study was to delineate whether the accessory molecule CD28 is involved in the impaired antigen response of T cells from patients with CVID. Our results demonstrate that CD28 costimulation was functional in T cells stimulated with anti-CD3 or anti-TCR MoAb, but could not correct the impaired response of patients' peripheral blood T cells to tetanus toxoid. Analysis of patients' long-term cultured T cells further confirmed these results. Exogenous rIL-2, another costimulus, augmented but did not correct the defective proliferation and lymphokine production in patients' antigen-driven peripheral blood T lymphocytes or in long-term cultured T cells. These findings indicate that the CD28 signalling pathway in these patients' T cells is unimpaired, and that costimulation via CD28 cannot correct the defect occurring in the course of TCR-mediated T cell activation.