B-cell Differentiation Factor Research Articles

Biological characterization of T cell-replacing factor in the synovial fluid of rheumatoid arthritis patients.

The synovial fluid of patients with rheumatoid arthritis (RA) contains a biologically active factor which has the ability to replace T cells for the induction of antibody secretion by human blood lymphoid cells stimulated by pokeweed mitogen (PWM) in vitro. This factor, which will be referred to as RA-SF (synovial fluid), also has the capacity to act as a B cell-stimulatory factor of mouse splenic lymphocytes in the presence of lipopolysaccharide (LPS). Using a test system developed for the definition of interleukin 4 (IL-4), which is a B cell-stimulating lymphokine which preferentially activates the synthesis of selected Ig classes in mouse lymphoid cells, we have shown that RA-SF has properties similar to IL-4 in that it induces differentiation of antibody secretion in the LPS-pretreated mouse cell, but unlike IL-4, which gives IgG1 and IgE, it selectively induces IgG2b synthesis. The present study demonstrates that RA-SF has a biological activity that is reminiscent of other B cell-stimulating mouse lymphokines, but it is biologically distinct from IL-2, IL-4, and IL-5. Recent data also indicate that it is distinct from gamma interferon (IFN-gamma). Therefore, we conclude that the biological activity of RA-SF has properties in common with a T-cell replacing (TRF) and B-cell differentiation factor (BCDF) and probably represents yet another biological activity which so far lacks an experimental counterpart. The relevance of this factor for autoantibody synthesis is discussed.

Human monoclonal antibodies produced by primary in vitro immunization of peripheral blood lymphocytes.

A general procedure is described for the production of human monoclonal antibodies from peripheral blood lymphocytes immunized in vitro against T-cell-dependent antigens. These lymphocytes immunized in culture were used to produce human-human or human-mouse hybridomas secreting monoclonal antibodies specific for digoxin, hemocyanin, a recombinant fragment of the gp120 envelope glycoprotein of human immunodeficiency virus (PB1), or a melanoma-associated antigen (p97). Depletion of a lysosome-rich cell population, containing large granular lymphocytes, monocytes, cytotoxic T cells, and a subset of CD8-positive T cells, was shown to be crucial before the cells could be immunized in vitro. This depletion was accomplished by treating the peripheral blood lymphocytes with the lysosomotropic agent L-leucine methyl ester. In addition, the in vitro immunization had to be supported by interleukin 2, gamma-interferon, and B-cell growth and differentiation factors, derived from irradiated, pokeweed-mitogen-stimulated human T cells. The production of human monoclonal antibodies from primary, antigen-specifically activated peripheral lymphocytes might obviate the need to immunize volunteers or patients.

Lymphokine-induction of memory B-cell differentiation: Differential stimulation of large virgin and memory B-cell differentiation

In order to compare and contrast the requirements of virgin and memory B cells for B-cell differentiation factors, a model system was developed in which low-density rat B cells isolated from 4-week primed antigen-draining lymph nodes were cultured in vitro. This large low-density cell population contained B cells which were 90% surface IgM positive and 60% IgD positive and showed moderately elevated Ia staining. When the cell population was stimulated with antigen plus lymphokines or lymphokines alone, antigen-specific IgG antibody was secreted; this was used as a measure of memory cell differentiation. When the cell population was stimulated with mitogen (lipopolysaccharide plus dextran sulfate) plus lymphokines, polyclonal IgG and IgM secretion was seen and was used as a measure of virgin B-cell differentiation. Using this system, we found that lymphokines contained in a Con A-induced rat spleen cell supernatant (CSN) were sufficient to drive both memory and virgin B-cell differentiation. In contrast, lymphokines contained in the supernatant from the murine T-cell hybridoma B151K12 (B151-CFS) were able to induce large amounts of polyclonal IgM and IgG secretion but did not support memory B-cell differentiation. When recombinant human IL-2 was added to these cultures, it acted synergistically to augment virgin B-cell differentiation, but this combination of lymphokines was still not able to support memory B-cell differentiation. Furthermore, recombinant rat interferon-γ and a commercial source of human BCGF, with or without IL-2, were unable to promote significant virgin or memory B-cell differentiation. These data support the hypothesis that memory B cells and virgin B cells differ in their lymphokine requirements for differentiation into antibody-secreting cells.

Inhibitory effect of anti-class II antibodies on human B-cell activation

The role of class II antigens for B-cell activation was analyzed using purified human B cells and anti-class II monoclonal antibodies. The stimulation of purified B cells with Staphylococcus aureus Cowan I induced proliferation and differentiation into immunoglobulin-producing cells in the presence of interleukin-1 and T-cell-derived factors (B-cell growth factor and B-cell differentiation factor). The addition of anti-class II monoclonal antibodies inhibited B-cell responses. However, anti-class I monoclonal antibody did not inhibit B-cell responses. When mitomycin C and cycloheximide-treated B cells were added to the induction culture of B cells as the stimulator, B-cell responses were enhanced in a dose-dependent manner. Furthermore, the stimulator B cells also partially restored the suppressed B-cell responses which were induced by the pretreatment of B cells with anti-class II antibody. This enhancing effect of stimulator B cells on B-cell responses was inhibited by the pretreatment of stimulator B cells with anti-class II antibody. The treatment of B cells with anti-class II antibody and complement depleted the activity of both responder B cells and stimulator B cells. These results suggest that cellular interaction among B cells exists in the B-cell activation induced with Staphylococcus aureus, Cowan I and anti-class II antibody inhibits B-cell activation by interfering in this cellular interaction.

Monocyte-Derived Human B-Cell Growth Factor Identified as Interferon-β 2 (BSF-2, IL-6)

Soluble products of either Epstein-Barr virus (EBV)-infected B cells or activated monocytes promote the proliferation of EBV-infected B cells and permit their growth at low cell densities. This suggests that growth factors are important for B-cell immortalization by EBV. In this study, a monocyte-derived factor that promotes the growth of EBV-infected b cells was purified and identified as interferon-beta 2 (IFN-beta 2), which is also known as 26-kilodalton protein, B-cell differentiation factor (BSF-2), and interleukin-6 (IL-6). The purified protein has a specific activity of approximately 4 X 10(7) units per milligram of protein in assays of B-cell growth. Thus, IFN-beta 2/BSF-2 is a B-cell growth factor that promotes the proliferation of human B cells infected with EBV.

Autoreactive T cell hybridoma-derived B cell stimulatory factor(s) governing IgA isotype immunoglobulin production by murine Peyer's patch B cells.

In the present study we investigated whether autoreactive T cells derived from murine Peyer's patches (PP) have the capacity to regulate mucosal B cell differentiation to IgA-producing plasma cells in vitro. We also examined whether B cell development is mediated by lymphokines from immunoregulatory T cells - that is, B cell stimulatory factors (BSF) and cofactors (coBSF) - which include B cell growth factor (BCGF), putative alpha B cell immunoglobulin (Ig) heavy chain switch factor (BSWF alpha), and B cell differentiation factor (BCDF), as well as interleukin-2 (IL-2). To this purpose we developed in vitro a variety of BSF (especially putative BSWF alpha)-producing autoreactive (self-class II molecules responsive) T cell hybridoma cell clones from murine PP, and studied the functional activity of the BSF, especially a putative alpha Ig heavy chain switch (mu----alpha) factors(s). These T hybridome cell lines possessed the surface phenotypes of Thy 1.2, CD4+, CD5+ and CD8- and produced a variety of BSF, including two kinds of BCGF (IL-5, and a BCGF that did not require additional costimulators to induce proliferation of preactivated B cells), putative BSWF alpha/gamma, BCDF, and/or IL-2. The results strongly support the view that the autologous T cell plays an important role not only in B cell proliferation and terminal maturation, but also in alpha heavy chain switching in PP. This T-B cell interation is mediated at least in part through BSF lymphokines elaborated by the autoreactive T cell, probably activated in situ in the lymphoid tissue microenvironment.

Cellular and genetic analyses of IL-2 production and IL-2 receptor expression in a patient with familial T-cell-dominant immunodeficiency

Cellular and genetic analyses of interleukin-2 (IL-2) production and IL-2 receptor (IL-2R) expression were examined in a immunodeficient patient and his family members. Mononuclear cells (MNC) of the patient showed no proliferative response (stimulation index, less than 2) to T-cell mitogens (PHA and Con A) and were defective in IL-2 production and IL-2R expression (less than 1%), whereas productions of other lymphokines (B-cell differentiation factor and IFN-γ) were not impaired significantly. His brother died of the same disease and his father also lacked in proliferative response and IL-2 production by PHA stimulation. In Southern blot analyses using DNA probes of IL-2 and IL-2R, patterns of the patient were the same as those of healthy volunteers, whereas the transcription of DNA coding for IL-2R to mRNA was lacking in the patient. These results suggest that inheritant defects of IL-2 production and IL-2R expression reside in this family and the defects are not linked to DNAs coding for IL-2 and IL-2R but to a transcriptional deficiency.

Interleukin-1 stimulation of human B-lymphoblast differentiation

Transformed B-cell lines have provided useful tools for analyzing B-cell responses to growth and differentiation factors. SKW 6.4 is a human B-lymphoblastoid line that differentiates in response to B-cell differentiation factor (BCDF) but not to other T-cell-derived lymphokines. The present studies were undertaken to determine whether monocyte-derived factors such as interleukin-1 (IL-1) could also promote the maturation of SKW 6.4 cells. Cells were cultured with and without supernatants derived from adherent monocytes of normal individuals. The number of Ig-producing plaque-forming cells in control media cultures gradually increased over a period of 4 days. Monocyte supernatants caused a 3- to 10-fold further increase in the number of IgM-secreting cells over that found in control media cultures. this stimulation by monocyte supernatants was maximal on the third or fourth day of culture and was not accompanied by an increase in proliferation. Recombinant IL-1 added to cultures of SKW 6.4 also produced a dose-related increase in the number of IgM-secreting cells without stimulating proliferation. A polyclonal antiserum against IL-1 prevented the increase in IgM-secreting cells which occurred with the addition of monocyte supernatants. Finally, IL-1 activity was detected in unstimulated SKW 6.4 supernatants. We conclude from these studies that SKW 6.4 cells both secrete IL-1 and differentiate in response to exogenous IL-1. SKW 6.4 may therefore provide a useful tool for future studies on mechanisms of IL-1-induced B cell maturation. It is possible that the basal numbers of IgM-secreting cells seen in unstimulated cultures results from an autocrine mechanism of IL-1-induced differentiation. Finally, care should be taken to exclude IL-1 from supernatants that are being tested for BCDF activity using SKW 6.4 cells.

Antigen processing: an interim report

Abstract The activation of B cells to synthesize and secrete antibody requires, in the vast majority of cases, the coincident activation of antigen-specific helper T cells to release B-cell growth and differentiation factors. Unlike antibody, which constitutes the B-cell receptor, the T-cell receptor does not bind globular protein antigens in their native conformations. Rather, the antigen must be fragmented or denatured and bound to the surface of an antigen presenting cell where it is recognized by the specific T cell in conjunction with a glycoprotein, Ia, encoded by the major histocompatibility gene complex (MHC). The molecular mechanisms by which antigen is processed and presented to T cells is now being unraveled, revealing the remarkable strategies employed for ensuring a specific immune response, and their possible application to the fundamental requirement for self-nonself discrimination.

Selective deficiency in IL-2 production and refractoriness to extrinsic IL-2 in immunodeficiency with hyper-IgM

Various lymphokines are inducible by the stimulation of T-cell mitogens, phytohemagglutinin, and concanavalin A. A 32-year-old female with an atypical type of immunodeficiency with hyper-IgM was evaluated for possible defects in the production of several immunoregulatory lymphokines. Although the mitogens appeared to bind effectively to the specific surface receptors of patient peripheral blood lymphocyte (PBL), the proliferative responses were significantly decreased. The culture supernatant of patient PBL stimulated by the mitogens contained only a trace amount of interleukin 2 (IL-2) activity. Addition of recombinant IL-2 to the cultures concomitantly with the mitogens could not restore the decreased responses of patient PBL. Tac antigen expression of patient PBL induced by the mitogens was moderately impaired. These data suggest that there is a defect in both IL-2 producing and IL-2-responding cells. In contrast, the culture supernatant of mitogen-stimulated patient PBL contained B-cell growth and differentiation factors as well as interferon-γ activities equal to those of the control. These results suggest that there are independent regulatory pathways for the production of IL-2 and other T-cell-derived lymphokines.

An immunomodulating anti-rheumatic drug, lobenzarit disodium (CCA): Inhibition of polyclonal B-cell activation and prevention of autoimmune disease in MRL/Mp-lpr/lpr mice

In this study, we examined the effect of an immunoregulatory antirheumatic agent, lobenzarit disodium (CCA), on spontaneously developing glomerulonephritis in MRL/Mp-lpr/lpr (MRL/l) mice. Starting from 6 weeks of age, mice were given CCA orally 5 days a week at a dose of 2 or 10 mg/kg. A control group was given the same volume of distilled water. The CCA treatment suppressed the excretion of protein in the urine. At 40 weeks of age, the incidence of proteinuria was 10 10 in the controls, 6 10 in the 2-mg/kg treatment group, and 5 10 in the 10 mg/kg group. The life span was prolonged dose dependently. The 50% survival time was 33 weeks for the controls, 35.5 weeks for the 2-mg/kg group, and 41 weeks for the 10-mg/kg group. The serum levels of anti-ssDNA antibody, anti-TNP antibody, and rheumatoid factor (RF) of the Ig G isotype and immune complex were reduced compared with control group. But the antibodies of Ig M isotype were not reduced. The serum Ig G1. Ig G2, and Ig G3 were significantly lower in the CCA-treated mice than in the controls. But again the serum level of Ig M was un-changed. These effects of CCA may be based on the suppression of lymphadenopathy. CCA may correct abnormal B-cell growth and differentiation factor release by the MRL l abnormal T cells. These results show that CCA inhibits the development of lupus nephritis in MRL l mice through the amelioration of the abnormal immune response, polyclonal B-cell activation.

Functional and biochemical characterization of B-cell differentiation factor (BCDF) produced by an HTLV-I-transformed human T-cell clone and demonstration of specific binding of the factor to a BCDF responsive cell line

We have previously described YA2, a human T-cell clone that secretes B-cell differentiation factor (BCDF) but not B-cell growth factor (BCGF). The BCDFs secreted by YA2 and HTLV-I-transformed YA2 (TYA2) were functionally similar in their ability to stimulate Ig secretion by Staphylococcus aureus Cowan strain I-activated B cells and IgM secretion by SKW6.4 cells. In addition, they were biochemically similar with a MW of 30 kDa by high-performance liquid chromatography (HPLC) sieving, and a p I of 6.0–6.8 by isoelectric focusing. The BCDF activity was not blocked by antibodies to interleukin 2 and BCGF. BCDF was purified from TYA2 supernatant by sequential media protein immunoadsorption, flat bed isoelectric focusing, HPLC TSK 2000 sieving, and repeated immunoadsorption and was then iodinated. The iodinated material had functional BCDF activity and migrated to a single band at MW 30 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and at p I of 6.8 by polyacrylamide gel isoelectric focusing. 125I-BCDF purified in this manner bound specifically to a BCDF-responsive cell line and not to phytohemagglutinin-activated T cells. 125I binding to the BCDF-responsive cell line was competitively inhibitable by the addition of cold BCDF. Thus we have purified and characterized a factor with BCDF activity and demonstrated that this factor binds specifically to a BCDF-responsive cell line.

Anti‐proliferative effects of interferons on Daudiburkitt Lymphoma cells: Induction of cell differentiation and loss of response to autocrine growth factors

Treatment of Daudi B-lymphoblastoid cells with low concentrations of either natural or recombinant human alpha-interferons inhibits cell proliferation and modulates the expression of a number of cell-surface antigens. Using a panel of monoclonal antibodies (MAbs) identifying determinants expressed at the surface of normal plasma cells, and polyclonal antibodies against surface and cytoplasmic immunoglobulin, we have found that growth inhibition is accompanied by plasmacytoid differentiation. Assays of growth stimulation of heterologous cells indicate that the culture medium from interferon-treated Daudi cells contains substantially more B-cell growth factor activity than that from control cells. However, the interferon-treated cells exhibit an impaired ability to respond to both these autocrine factors and exogenous factors produced by another Burkitt lymphoma line. These findings show that, in the case of Daudi cells, growth inhibition by interferons is closely associated with both terminal differentiation and a refractoriness to growth factors. In this system IFN-alpha may therefore be considered to be a B-cell differentiation factor, suggesting a possible basis for the anti-proliferative effects observed with certain human B-cell malignancies.

T cell-derived B cell growth and differentiation factors.

In the last few years it has been demonstrated that clonal expansion of B lymphocytes and their differentiation into antibody-producing cells are regulated by a complex series of soluble products released by T cells. The application of cloning and recombinant DNA techniques has made it possible to obtain most of these molecules in a purified form and, therefore, to study in more detail their functional properties. To date, three distinct T cell-derived B cell growth factors (BCGFs) and/or B cell differentiation factors (BCDFs), i.e., IL-2, IL-4 and IL-5, have been reported for mouse B cells. Likewise, at least five distinct molecules showing BCGF and/or BCDF activity (IL-2, IFN-gamma, IL-4, the 12 kD-BCGF and BSF-2) for human B cells have been identified. Human T cell-derived lymphokines active on B cells are functionally similar but not identical to murine lymphokines. Most T cell-derived lymphokines can exert their activity on the same B cells in different stages of activation and evoke different responses. In addition, some of them are not specific for B cells, but act as competence factors or competence cofactors for different hemopoietic cell lines. Finally, convincing evidence is accumulating to suggest that both activated and resting B cells may have receptors for BCGFs and BCDFs. This makes it clear why although the goal of a directed immune response is to generate antigen-specific antibodies, a large part of this response can actually be polyclonal and nonspecific.

Humoral immune response in patients with hemophilia

Hemophiliacs require frequent infusions of allogeneic proteins to control bleeding. Previous reports have demonstrated that thymus-derived lymphocytes (T cells) from hemophiliacs are antigenically primed to the lyophilized antihemophilic factor and that natural killer cells from hemophiliacs demonstrate impaired response to interferon-β and -γ Some aspects of the humoral immune response were investigated in eight patients who require large amounts of Factor VIII. Polyclonal hypergammaglobulinemia was detected in six patients and seven had elevated titers of autoantibodies of various specificities. There was no evidence of impaired concanavalin A-inducible T-suppressor cell activity. Polyclonal immunoglobulin secretion secondary to pokeweed mitogen in vitro was elevated in three of eight patients and depressed in five. Spontaneous production of both B-cell growth and differentiation factors (BCGF and BCDF) was elevated but mitogen-induced production was impaired. These data demonstrate that the humoral immune response of hemophiliacs may be chronically stimulated, thus impairing their ability to respond to new antigens such as viruses.

T cell replacing factor/interleukin 5 induces not only B-cell growth and differentiation, but also increased expression of interleukin 2 receptor on activated B-cells

A T-cell replacing factor (TRF)/interleukin-5 (IL-5) is a B-cell growth and differentiation factor. In the present study, we examined the role of TRF/IL-5 in the increase in the levels of interleukin-2 (IL-2) receptor expression on activated B-cells. High pressure liquid chromatography (HPLC)-purified TRF/IL-5 (B151-TRF) from TRF-producing T-cell hybridoma, B151K12, as well as recombinant TRF/IL-5 (rec-TRF) were used for the analysis. Maximum anti-2,4-dinitrophenyl (DNP) IgG antibody response of DNP-primed B-cells or polyclonal IgM secretion of B-cell tumor line BCL 1 was seen when HPLC-purified B151-TRF was added or when suboptimal doses of B151-TRF were added to the culture in the presence of IL-2. Normal resting B-cells gave maximum anti-SRBC IgM PFC responses when HPLC-purified B151-TRF and IL-2 were present. The purified B151-TRF as well as rec-TRF also induced on B-cells increased expression of IL-2 receptors that react with monoclonal anti-murine IL-2 receptor antibody, PC61, and 125I-labelled IL-2. The numbers of functional high affinity IL-2 receptors on activated B cells increased at least 20-fold by culturing them with purified B151-TRF. Moreover, B151-TRF induced increase in the levels of steady-state mRNA for IL-2 receptor by approximately 8-fold. These results suggest that activated B-cells as well as BCL 1-cells may express functional IL-2 receptors or closely related molecules when stimulated with HPLC-purified B151-TRF as well as rec-TRF.

The characterization of a human B cell line utilizable for the assay of B cell growth factors

An EBV-transformed B cell line JR-2(82) is described which proliferates in response to human B cell growth factor (BCGF) preparations. Although spontaneous replication occurs at high cell densities, at cell densities of 10 3 cells or less, cell death occurs in the absence of BCGF. This response is not dependent upon the presence of low concentrations of supplemental serum in the culture medium. There is no proliferative response to various preparations of interleukin (IL)-1, IL-2 or γ-interferon (γ-IFN) up to 1000 U/ml either alone or in combination and specific antisera to IL-2 and γ-IFN do not interfere with the proliferative response. At 5000 U/ml of γ-IFN or greater, a partial proliferation of the line is seen to 30% of maximal. The JR-2(82) line and its clones appear to proliferate preferentially in response to low molecular weight (LMW) BCGF, compared to the response seen to high molecular weight (HMW) BCGF from Namalwa cell line supernatants. The line does not produce Ig spontaneously but on incubation with B cell differentiation factor (BCDF) containing supernatants differentiates to an IgG-producing cell line. JR-2(82) or its derivatives may therefore provide a simple reproducible assay for BCGF in the presence of other lymphokines and may be used to study further the interactions of lymphokines in the regulation of the proliferation of EBV-transformed cells.

Rapid enhancement of beta 2-interferon/B-cell differentiation factor BSF-2 gene expression in human fibroblasts by diacylglycerols and the calcium ionophore A23187.

The expression in human fibroblasts of the beta 2-interferon (IFN-beta 2) gene, which is now recognized to be identical to the gene encoding B-cell differentiation factor BSF-2, is enhanced by several cytokines that affect cell growth (tumor necrosis factor, interleukin 1, platelet-derived growth factor, and beta 1-interferon). We have examined the possibility that IFN-beta 2 gene expression is regulated through activation, by diacylglycerol, of the protein kinase C pathway. The synthetic diacylglycerols 1,2-dioctanoylglycerol (diC8) and 1-oleoyl-2-acetylglycerol strongly enhanced IFN-beta 2, but not IFN-beta 1, gene expression in human fibroblasts (FS-4 strain). An increase in IFN-beta 2 mRNA level was detected within 15 min after addition of diC8 (290 microM) to FS-4 cells and was maximal approximately 20 hr later. An increase in IFN-beta 2 gene transcription was detected within 5 min of addition of diC8, and the rate of transcription was near-maximal by 15-30 min. The enhancement of IFN-beta 2 gene expression by diC8, interleukin 1, or tumor necrosis factor was not prevented by H8, a preferential inhibitor of cAMP- and cGMP-dependent protein kinases, but was blocked by H7, an inhibitor of protein kinase C as well as of cyclic nucleotide-dependent protein kinases. diC8 was found to protect FS-4 cells from the cytopathic effect of vesicular stomatitis virus; this protection was blocked by polyclonal or monoclonal antibodies that neutralize IFN-beta, suggesting that the antiviral effect was due to the secretion of IFN-beta 2 by the diC8-treated fibroblasts. The calcium ionophore A23187 (1-10 microM) also elicited an increase in the level of IFN-beta 2 mRNA in FS-4 fibroblasts; appropriate combinations of A23187 and diC8 had at least an additive effect in enhancing IFN-beta 2 mRNA levels. These results show that protein kinase C-activating or [Ca2+]-elevating agents rapidly increase the expression of the IFN-beta 2 gene in human fibroblasts.

Age-associated changes in proliferative and differentiative response of human B cells and production of T cell-derived factors regulating B cell functions

The abilities of highly purified B cells to repeat replication for clonal expansion and to differentiate into immunoglobulin secreting cells (ISC) were examined in the aged and young groups. B cells from the aged showed twofold less proliferative response to B cell mitogen Cowan 1 (SAC) than those from the young. The original clone size of SAC responding B cells determined by colchicine block and [ 3H] thymidine ([ 3H] TdR) uptake was not significantly reduced in the aged whereas the ability to repeat replication to expand clonal size was significantly reduced. B cells from aged and young persons were induced into ISC by combined stimulation with SAC and partially purified B cell differentiation factor (BCDF) free of IL-2 activity. ISCs for IgG and IgA were rather increased or at least not reduced in number in the aged as compared with those in the young. We also determined the IL-2 and BCDF activity produced by T cells from aged and young persons. Upon PHA stimulation, the aged T cells produced tenfold less IL-2 activity and threefold higher BCDF activity than did young T cells. Approximately threefold increase in spontaneous secretion of BCDF activity by aged T cells was found as compared with young T cells. The inverse correlation between the IL-2 activity and BCDF activity was found when both activities were determined in the same samples.

The effects of cytokines and adherent cells on the interleukin 4-mediated induction of Ia antigens on resting B cells

In this report we have extended our previous studies on interleukin 4 (IL-4) [previously termed B-cell stimulatory factor-1 (BSF-1)]. Our results demonstrate that 8 hr of exposure to IL-4 is sufficient to induce maximal expression of Ia antigens. This increase in expression of Ia antigens on resting B cells is due to the direct action of IL-4 on the B cells since adding or removing adherent cells or utilizing low density cultures of B cells at 50–100/culture had no effect on the IL-4-mediated increase in Ia. Monoclonal anti-IL-4 antibody completely abrogated the Ia-inducing activity of IL-4. A variety of other purified lymphokines including interleukin 2 (IL-2), interleukin 1 (IL-1), and a source of either B-cell differentiation factor for IgM (BCDFμ), or B-cell growth factor II (BCGF II), did not alter the expression of Ia antigens on resting B cells. However, interferon-γ can partially inhibit the IL-4-mediated induction of Ia.