A mouse T cell product that preferentially enhances IgA production. I. Biologic characterization

Supernatants from a subset of helper T cell clones can enhance IgA, IgE, and IgG1 production in cultures of lipopolysaccharide-stimulated, T cell-depleted spleen cells. The lymphokine interleukin (IL)-4 has been shown to cause the IgE and IgG1 enhancement produced by these supernatants. IgA enhancement, however, is mediated by a factor distinct from IL-4, although IL-4 can potentiate the effect of the IgA-enhancing factor. IgA-enhancing factor is also distinct from IL-1, IL-2, IL-3, granulocyte-macrophage colony-stimulating factor, and interferon-gamma and acts directly on B cells. Purified IgA-enhancing factor enhances IgA production three- to sixfold yet causes less than a twofold increase in other isotypes. The IgA enhancing activity is not inhibited by concentrations of interferon-gamma that inhibit IL-4 activities. In the accompanying article, we show that this IgA enhancing activity is a novel property of the lymphokine IL-5.     

Interleukin 5 and interleukin 4 produced by Peyer's patch T cells selectively enhance immunoglobulin A expression

Considerable evidence suggests that the high frequency of B cells committed to the IgA isotype in Peyer's patches is regulated by T lymphocytes. To understand more accurately the mechanism of this immunoregulation, an autoreactive T cell line from Peyer's patches was generated by culturing L3T4+ Peyer's patches T cells with syngeneic B cell blasts. The resulting T cell line, designated PT-1, and a clone derived from this line, PT-1.14, stimulated immunoglobulin secretion in spleen B cells with a preferential enhancement of IgA and IgG1 isotypes. Supernatant derived from concanavalin A-stimulated PT-1 or PT-1.14 cells could also enhance IgA secretion if spleen B cells were preactivated with lipopolysaccharide. Peyer's patches T cell supernatant did not contain IgA-specific binding factors. PT-1 supernatant scored positive in lymphokine assays for interleukin (IL)-2, IL-4 (B cell stimulatory factor 1), IL-5 (B cell growth factor II), and interferon-gamma, whereas PT-1.14 supernatant was positive for IL-4 and IL-5 and negative for IL-2 and interferon-gamma. Only IL-5 enhanced IgA secretion in lipopolysaccharide-activated B cells and this response was increased two- to three-fold by IL-4. These results suggest that the type 2 T helper subset which produces both IL-5 and IL-4 plays a primary role in regulating IgA expression.     

Human low molecular weight B cell growth factor induces surface IgM+/A- B cells to express and secrete IgA.

The regulation of Ig class expression has been a controversial area of research. It is well established that T cells, and/or their products, influence which Ig isotype is produced during an immune response. In this study the regulation of Ig secretion of activated human IgM+/A- B cells was examined. Human T cell supernatants induced PWM-activated IgM+/A- B cells to switch to IgA secretion. Purification of the lymphokine mediating this effect involved hydroxylapatite, ion exchange, and gel filtration chromatography. The purified lymphokine could induce switch of IgM+/A- B cells, and it was also capable of inducing proliferation of Staphylococcus aureus Cowan 1 strain (SAC)-activated IgM+/A- B cells. SDS-PAGE and isoelectric focusing indicated the protein mediating this activity had a molecular mass of approximately 14 kDa and a pI of 6.8. These results suggested that the observed activity might be due to low m.w. B cell growth factor (LMW-BCGF), a lymphokine which is capable of inducing proliferation of SAC-activated B cells and has a molecular weight and pI value in the range of the purified protein. Indeed, rLMW-BCGF was able to switch IgM+/A- B-cells to IgA expression and secretion as well as induce the proliferation of SAC-activated IgM+/A- B cells. These results demonstrate that LMW-BCGF is capable of inducing PWM-activated IgM+/A- B-cells to switch to IgA possibly by providing a proliferation signal which induces clonal expansion of IgM+/A- B cells, the progeny of which express a range of isotypes including IgA. This study also demonstrates that lymphokine induced isotype switching involves an intermediate stage of B cell development where human B cells coexpress IgM and a downstream isotype on their surface.     

Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins

A panel of antigen-specific mouse helper T cell clones was characterized according to patterns of lymphokine activity production, and two types of T cell were distinguished. Type 1 T helper cells (TH1) produced IL 2, interferon-gamma, GM-CSF, and IL 3 in response to antigen + presenting cells or to Con A, whereas type 2 helper T cells (TH2) produced IL 3, BSF1, and two other activities unique to the TH2 subset, a mast cell growth factor distinct from IL 3 and a T cell growth factor distinct from IL 2. Clones representing each type of T cell were characterized, and the pattern of lymphokine activities was consistent within each set. The secreted proteins induced by Con A were analyzed by biosynthetic labeling and SDS gel electrophoresis, and significant differences were seen between the two groups of T cell line. Both types of T cell grew in response to alternating cycles of antigen stimulation, followed by growth in IL 2-containing medium. Examples of both types of T cell were also specific for or restricted by the I region of the MHC, and the surface marker phenotype of the majority of both types was Ly-1+, Lyt-2-, L3T4+, Both types of helper T cell could provide help for B cells, but the nature of the help differed. TH1 cells were found among examples of T cell clones specific for chicken RBC and mouse alloantigens. TH2 cells were found among clones specific for mouse alloantigens, fowl gamma-globulin, and KLH. The relationship between these two types of T cells and previously described subsets of T helper cells is discussed.     

Two independent pathways of helper activity provided by a single T cell clone

Data presented in this paper demonstrate the existence of two separate pathways by which a single T cell clone can induce B cell differentiation. With the use of high doses of antigen, a T cell clone can induce a primary antibody response in unprimed B cells. With the use of low doses of antigen, the same T cell clone can induce an immunoglobulin (Ig)G response in primed B cells. The primary response is accompanied by T cell proliferation and lymphokine production (interleukin 2, B cell growth factor, B cell differentiation factor for immunoglobulin M, and B cell differentiation factor for immunoglobulin G). The secondary response does not require proliferation and occurs independently of detectable lymphokine production. Variants of the wild type T cell helper clone have been isolated. One variant can provide help to unprimed B cells when high doses of antigen are used. This variant cannot provide help to primed B cells when low doses of antigen are used, nor can it provide help to CBA/N "xid" B cells at any antigen concentration tested. Additional variants have been isolated that proliferate on antigen-pulsed-presenting cells, but fail to secrete detectable lymphokines and do not induce B cell differentiation. These results suggest that a single T cell helper clone has multiple functional activities that can be independently expressed.     

Human peripheral blood monocytes release a 30,000 dalton factor (30 KD MF) that stimulates immunoglobulin production by activated B cells

Supernatants (SN) of well-washed adherent human monocytes, obtained from T cell-depleted peripheral blood mononuclear cells, contain a 30,000 dalton protein (30 KD MF) that increases immunoglobulin (Ig) synthesis by EBV-activated B cells two- to fourfold. This factor is released spontaneously during the first 20 hr after monocytes are placed in culture. SN containing 30 KD MF are inactive in the thymocyte co-stimulator assay, under conditions that will detect as little as 0.5 U of purified IL 1. The addition of autologous T cells to isolated adherent monocytes, previously depleted of T cells, suppresses the release or activity of this B cell stimulator in a dose-dependent manner. In addition, 30 KD MF stimulates a two- to fourfold increase in IgA production by cells of an EBV-transformed B cell line (JB/FF line) without increasing incorporation of [3H]thymidine. In contrast, stimulation of this B cell line with up to 10 U of purified IL 1 increases IgA synthesis by less than 50%, and addition of up to 100 U of recombinant IL 2 causes no change whatsoever in IgA production. However, co-stimulation with 30 KD MF and recombinant IL 2 or recombinant gamma-interferon induces more Ig production than is caused by the monocyte factor alone. These observations suggest that the monocyte, in addition to acting as an antigen-presenting cell and source of IL 1, facilitates B cell differentiation by producing a factor which acts both independently and in synergy with cytokines produced by T cells to stimulate Ig production by B lymphocytes.     

Antigen-specific, MHC-restricted B cell activation by cell-free Th2 cell products. Synergy between antigen-specific helper factors and IL-4

Ag-specific and MHC-restricted Th clones of different Ag specificities and MHC haplotypes were tested for their ability to produce soluble factors capable of providing the signals required for B cell activation and IgG antibody production. Each of five Th clones tested generated significant helper activity in supernatants derived from coculture of the T cell clone with specific Ag and syngeneic APC. The same helper activity was detected in supernatants of clones stimulated with immobilized anti-CD3 antibody in the absence of Ag or APC. The secreted helper activity resembled the activity of the intact Th cells in that it was Ag-specific, carrier-hapten-linked and MHC-restricted. These T cell products functioned to activate only those B cells expressing MHC products which corresponded to the specificity of each Th clone. Thus, the specificity of the cell-free T cell product mimicked precisely that expressed by the intact Th cell and presumably mediated by the cell surface TcR. In addition to the apparent presence of specific helper factor in Th clone supernatants, a role for nonspecific lymphokines was also identified in these preparations. Although recombinant or purified IL-4 alone was not sufficient to stimulate hapten-primed B cells to secrete hapten-specific IgG antibodies, mAb specific for IL-4 blocked the induction of antibody secretion by Th cell supernatant. These results indicate that stimulation of B cells to produce hapten-specific IgG antibody requires at least two distinct signals: an Ag-specific T cell signal which is restricted by MHC products expressed on the B cells, and a nonspecific signal mediated at least in part by the lymphokine IL-4.     

Regulation of B cell maturation and differentiation. I. Suppression of pokeweed mitogen-induced B cell differentiation by tumor necrosis factor (TNF)

Growth and differentiation of B cells into Ig-secreting plasma cells is regulated by both T cells and macrophages and/or their secreted factors. Although the regulatory role of various cell-derived factors has been examined, the involvement of the macrophage-derived factor, TNF, in human B cell growth and differentiation has not yet been investigated. In the present study we examine the role of rTNF in polyclonal B cell response of human PBL induced by PWM. The addition of rTNF at the initiation of the culture resulted in the dose-dependent inhibition of the generation of both IgG and IgM PFC. Inhibition of PFC development followed the same dose response as rTNF-mediated cytotoxicity against a TNF-sensitive tumor target. The mechanism of rTNF-mediated suppression was examined in different experimental systems. Recombinant TNF did not affect the viability or proliferation of either the T cell or B cell subpopulations, suggesting that TNF does not mediate its suppressive effect by cytotoxic mechanisms. Kinetic studies in which rTNF was added at different times after initiation of culture indicated that inhibition can be observed as late as 4 days of culture and suggested that TNF acts at a late phase of the growth and differentiation pathway of B cells. In further studies we examined the cellular level of TNF-mediated suppression. The addition of rTNF to supernatants containing helper factors and enriched B cells resulted in no inhibition, suggesting that TNF does not act at the B cell level. This was confirmed by demonstrating that rTNF does not inhibit spontaneous PFC development by the CESS B cell line. The effect of TNF on T cell subpopulations was examined by using normal or irradiated T cells, which inactivate suppressor cells. Addition of rTNF to B cells combined with either T cell population suppressed both IgG and IgM PFC development, indicating that the target cell for suppression is the T helper cell but not ruling out an effect on macrophages or the T suppressor cells. Combined, the observed results demonstrate that rTNF suppresses PWM-induced B cell differentiation without affecting B cell proliferation. TNF appears to mediate the suppression by acting directly on T helper cells or else by regulating the production of factors controlling T cell activation and lymphokine secretion.     

B cell stimulatory factor-1 enhances the IgE response of lipopolysaccharide-activated B cells

Supernatants from some mouse helper T cell (TH) lines contain an activity that can enhance IgE production by lipopolysaccharide (LPS)-stimulated B cells by at least two orders of magnitude. During purification, this activity could not be resolved from B cell stimulatory factor-1 (BSF-1). Highly purified BSF-1 from a different source, the T lymphoma cell line EL-4, enhanced IgE production to the same extent as TH supernatants, which suggests that BSF-1 is responsible for this increase in IgE production. Monoclonal antibody to BSF-1 totally inhibits the IgE-enhancing activity of a TH supernatant, lending further support to this conclusion. The effects of BSF-1 on LPS-stimulated B cells are specific for IgE and, as previously reported, IgG1 and IgG3, because the levels of IgM, IgG2a, IgG2b, and IgA in the cultures change relatively little when BSF-1 is added.     

Retrovirus-mediated immunosuppression. II. FeLV-UV alters in vitro murine T lymphocyte behavior by reversibly impairing lymphokine secretion

Murine splenocytes and cloned murine T cells were used to study the in vitro immunosuppressive effects of UV-inactivated feline leukemia virus (FeLV-UV) on lymphokine secretion. FeLV-UV can significantly depress the accumulation of IL 2 in cultures of Con A-stimulated C57BL/6 splenocytes and in cultures containing the alloreactive helper T cell clone B6D/2-2m plus Con A. Inhibition of lymphokine accumulation in these cultures could not be attributed to absorption or inactivation of IL 2 by the FeLV-UV or to the FeLV-UV-induced production of substances which interfere with the IL 2 bioassay. Thus, FeLV-UV appears to block production and/or secretion of IL 2 by a direct inhibitory effect on IL 2-secreting murine T lymphocytes. Additional studies indicate that FeLV-UV impairs IL 2 production only if added very soon after lymphocyte contact with lymphokine-inducing agents and that IL 2 secretion resumes when FeLV-UV is removed from the culture. FeLV-UV also impairs accumulation of MAF (interferon-gamma?) in cultures of Con A-stimulated C57BL/6 splenocytes and in cultures containing the alloreactive cytotoxic T lymphocyte clone B6D/2-7c plus Con A. The latter observation again suggests that FeLV-UV impairs lymphokine secretion by a direct effect on lymphokine-producing T lymphocytes. Furthermore, it suggests that FeLV-UV does not selectively impair production of IL 2 nor does it have selective inhibitory effects on helper T cells. Rather, FeLV-UV appears to have a general inhibitory effect on lymphokine production by T lymphocytes. Finally, concentrations of FeLV-UV which suppress MAF production by the CTL clone have little influence on the cytolysis mediated by the same cloned T cell population. Thus, the immunosuppressive influence of FeLV-UV is selective for phenomena associated with induction of new T lymphocyte functions, such as lymphokine secretion, and spares other immune functions already expressed by the same cells.     

Triggering of affinity-enriched B cells. II. Composition and B cell triggering properties of affinity-purified, antigen-specific, T cell-derived helper factor

Antigen-specific, T cell-derived helper factor (ASHF), recognizing alloantigens on chicken red blood cells (CRBC), had previously been shown to trigger an IgM anti-CRBC response in vitro by 2 X 10(3) affinity-enriched B cells. Triggering signals for B cell proliferation were shown to be substituted by ASHF or lipopolysaccharide, and signals for differentiation to IgM production by Thy-1+ cells. In an effort to demonstrate unequivocally antigen specificity of helper factor, secretory products and cell extracts from helper T cells that had been primed by either the B2 or the B13 chicken alloantigens, were purified by antigen affinity and ion exchange chromatography. With each step of purification, antigen-specific biologic activity of ASHF-containing material increased such that ASHF from B2, but not B13, primed helper T cells would help trigger a B2, but not a B13, -specific response and vice versa. Gel filtration of ASHF suggests it to have a m.w. of at least 50,000. Absorption studies showed that ASHF binds to B cells in the absence of antigen. Delivery of the triggering signal requires ASHF to bind simultaneously to both, the cell surface and the antigen. ASHF consists of at least two subunits that may be separated from each other by chelating agents. This yields two biologically inactive fractions, only one of which binds to the nominal antigen. Upon recombining them in the presence of Ca++, full biologic activity is restored.     

Correlation between the biologic functions and the generation of lymphokines in T cell clones

We have recently reported that various murine T cell clones produce IL-1. Based on this observation we have analyzed in the present study the correlation between the biological functions and the generation of different lymphokines in (T,G)-A--L specific CD4+ clones. One subset of clones--the "helper clones"--were found to provide help to primed B cells, in vitro. These cells could be shown to produce IL-1, IL-2, and B cell stimulatory factor 1 (IL-4) activities and to express mRNA encoding for these three cytokines. The second subset of clones, termed "proliferative clones", were unable to help B cells in vitro but expressed vigorous Ag-dependent proliferations. These cells did not express IL-1, IL-2, or IL-4 activities. They produced another lymphokine(s) which may be granulocyte-macrophage-CSF, or some other factor recognized by the HT2 cell line. This study further substantiates the link between T cell activities and lymphokine repertoire with a special emphasis on the potential role(s) of T cell-derived IL-1.     

B lymphocyte regulation of the immune system. II. Inhibition of Fc receptor expression of lymphocytes by BEF, a lymphokine of B cell origin

Recently, we described a new lymphokine of B cell origin, capable of selectively preventing the differentiation of T suppressor cells from the precursor into the effector stage. As a result, antibody production against various antigens is markedly increased. We termed this lymphokine B cell-derived enhancing factor (BEF). To discern the mechanism(s) by which BEF interferes with the activation of T suppressor cells, experiments were undertaken to explore the effect of BEF on the induction of Fc receptors (FcR). The induction of FcR on T cells has been implicated in the down-regulation of antibody synthesis, and it has been suggested that the expression of FcR for a given immunoglobulin precedes the release of factors with regulatory functions for the corresponding isotype. In the experiments reported here, murine spleen cells were incubated for 24 hr in the presence of IgG1 or IgA monoclonal antibodies, were washed, and the number of FcR gamma 1+ and FcR alpha+ cells were calculated by a rosette assay. The effect of BEF was studied either during the inductive phase or before, i.e., by pretreating the cells with BEF for 18 hr at 37 degrees C before the inductive phase. Our results show that BEF abolishes, in a dose-dependent manner, the expression of isotype-specific FcR in spleen cells when present during the inductive phase, as well as when cells are pretreated with it. In successive experiments, we tested the effect of BEF on the induction of FcR on T cell-enriched or B cell-enriched spleen cells. The results show that BEF is effective in selectively inhibiting FcR expression on T lymphocytes, but not on B lymphocytes, once isolated from the total spleen cell population. These findings provide further insight into the mechanism by which BEF modulates the immune response, and suggest that different mechanisms may be involved in the induction of FcR on T and B lymphocytes, respectively.     

Transforming growth factor-beta directs IgA switching in human B cells.

Transforming growth factor (TGF)-beta added to cultures of highly purified human splenic B cells induced high levels of IgA synthesis in the presence of PWM and activated cloned CD4+ T cells. TGF-beta had no effect on IgM or IgG production. The induction of IgA synthesis by TGF-beta reflected IgA switching, because a strong induction of IgA production was also observed, when sIgA- B cells were cocultured with cloned activated CD4+ T cells in the presence of pokeweed mitogen. Resting CD4+ T cell clones or activated CD8+, TCR-gamma delta + CD4-,CD8- T cell clones failed to provide the co-stimulatory signal that in addition to TGF-beta and pokeweed mitogen was required for induction of IgA switching and IgA synthesis. mAb against CD4 or class II MHC molecules inhibited TGF-beta induced IgA synthesis, indicating that CD4-class II MHC interactions are required for productive T-B cell contacts resulting in IgA production. In contrast, anti-LFA-1, anti-CD2, and anti-class I MHC mAb were ineffective. TGF-beta failed to induce IgA synthesis by sIgA+ B cells under these culture conditions. Interestingly, induction of IgA production by sIgA- B cells required neutralization of TGF-beta activity by addition of the anti-TGF-beta mAb 1D11.1G 24 h after onset of the cultures. IgA production was prevented when the anti-TGF-beta mAb was added at the start of the cultures, indicating the specificity of the reaction. IgA synthesis was completely suppressed when TGF-beta was present during the total culture period of 11 days. These findings indicate that TGF-beta can act as a specific switch factor for IgA, provided it is only present at early stages of the cultures.     

B cell maturation factor (BMF): a lymphokine or family of lymphokines promoting the maturation of B lymphocytes

Two in vitro B cell tumor lines have been used to characterize and partially purify a lymphokine, or family of lymphokines, from monoclonal helper T cell immune response supernatants. These lymphokines induce the pre-B-like 70Z/3 tumor cell to synthesize Ig L chains and express complete Ig molecules on its cell surface, and cause the mature B cell-like WEHI-279 tumor cell to increase its ratio of secretory to membrane mu production, begin high rate Ig secretion, and then die. Most of the activity responsible for these changes co-purifies during five different separation procedures, implying the existence of a discrete molecule or closely related class of molecules able to mediate all of these effects. The molecules active in these systems appear distinct from the other lymphokines IL 1, IL 2, G/M-CSA, TRF, IFN, BCGF, and the activity variously termed IL 3/BPA/PSF/HCGF/MCGF, etc. We call these B cell-differentiating molecules BMF, or B cell maturation factor(s). The BMF molecules are mildly acidic (pI 5 to 6 in various conditions), extremely hydrophobic, probably heterogeneously glycosylated glycoproteins, with an apparent m.w. of 50,000 to 55,000 by gel permeation chromatography and 16,000 by SDS-PAGE. BMF has been purified approximately 3000-fold by three sequential chromatographic steps, with the use of the B tumor line assay systems. BMF molecules thus purified also cause normal resting splenic B cells to mature to the state of active Ig secretion.     

MLC-derived human helper factor(s) that promote B cell differentiation: induction, functional characterization, and role of Ia antigens

Utilizing a PFC assay to quantitate the polyclonal activation of human peripheral blood B lymphocytes, we have investigated the induction and functional activity of MLC-derived human helper factor(s). Our data demonstrate that highly purified responder T cells, but not B or null cells, are required for the elaboration of MLC helper factor(s) that trigger the in vitro differentiation of B lymphocytes into PFC. Helper factor can trigger B cell maturation in the absence of helper T cells, since complement- (C) mediated lysis of the small (less than 5%) fraction of T cells present in anti-F(ab)2 immunoabsorbent column purified B cell population eliminates the PWM induced, but not the helper factor-induced PFC response. Responder T cells required for helper factor production do not bear surface membrane Ia, since alpha p23,30 + C treatment of this population does not affect helper factor generation. In contrast, alpha p23,30 + C treatment of the allogeneic stimulator cell population eliminates helper factor production. Taken together, these results demonstrate that interaction between Ia-bearing stimulator cells and Ia- responder T cells is required for the production of MLC-derived helper factor. In additional experiments, we determined that alpha p23,30, in the absence of C, totally abrogates the PFC response triggered by MLC helper factors. This result suggests an important role for Ia antigens in the functional activity of preformed helper factor molecules.     

CD40 stimulation provides an IFN-gamma-independent and IL-4-dependent differentiation signal directly to human B cells for IgE production.

IgE induction from human cells has generally been considered to be T cell dependent and to require at least two signals: IL-4 stimulation and T cell/B cell interaction. In the present study we report a human system of T cell-independent IgE production from highly purified B cells. When human cells were co-stimulated with a mAb directed against CD40 (mAb G28-5), there was induction of IgE secretion from purified blood and tonsil B cells as well as unfractionated lymphocytes. Anti-CD40 alone failed to induce IgE from blood mononuclear cells or purified B cells. The effect of the combination of anti-CD40 and IL-4 on IgE production was very IgE isotype specific as IgG, IgM, and IgA were not increased. Furthermore, anti-CD40 with IL-5 or PWM did not co-stimulate IgG, IgM, or IgA and in fact strongly inhibited PWM-stimulated IgG, IgM and IgA production from blood or tonsil cells. IgE synthesis induced by anti-CD40 plus IL-4 was IFN-gamma independent as is the in vivo production of IgE in humans; the doses of IFN-gamma that profoundly suppressed IgG synthesis induced by IL-4, or IL-4 plus IL-6, had no inhibitory effect on anti-CD40-induced IgE production. Anti-CD23 and anti-IL-6 also could not block anti-CD40 plus IL-4-induced IgE production, but anti-IL-4 totally blocked their effect. IgE production via CD40 was not due to IL-5, IL-6 or nerve growth factor as none of these synergized with IL-4 to induce IgE synthesis by purified B cells. Finally, we observed that CD40 stimulation alone could enhance IgE production from in vivo-driven IgE-producing cells from patients with very high IgE levels; cells that did not increase IgE production in response to IL-4. Taken together, our data suggest that the signals delivered for IgE production by IL-4 and CD40 stimulation may mimic the pathway for IgE production seen in vivo in human allergic disease.     

Lymphokine-mediated activation of a T cell-dependent IgA antipolysaccharide response

Immune responses to bacterial polysaccharides are important to host immunity at mucosal surfaces. We previously showed that BALB/c mice produce substantial T cell-dependent IgA responses to alpha (1,3) glucan determinants on the bacterial capsular polysaccharide dextran B1355. The data in this study demonstrate that the requirement for T cells for the activation of the IgA anti-alpha (1,3) dextran B1355 response can be replaced by T cell-derived nonantigen specific helper factors that appear to act during the late stages of B cell differentiation. Supernatants from the activated T cell lines cr-15 and (DL)C.C3.11.75, which contain interferon and late-acting T cell replacing factor activity, supported terminal differentiation of dextran-stimulated B cells to IgA anti-alpha (1,3) glucan antibody-forming cells and substantially increased IgM anti-alpha (1,3) glucan responses in culture. Although supernatants with interleukin 2 activity did not support optimal antigen-driven plaque-forming cell responses, they synergized with supernatants having interferon and T cell replacing factor activity in the production of IgA and IgM anti-alpha (1,3) glucan responses and IgM anti-SRBC responses. Supernatants from the T cell lines B6.11 and (DL)A.4 contained B cell growth factor activity but did not support activation of IgA anti-alpha (1,3) glucan PFC. These studies suggest that interferon and/or T cell replacing factor play an important role in the antigen-driven differentiation of B cells of the IgA and IgM isotypes to antibody-forming cells.     

Lymphokines: their role in lymphocyte responses. Properties of interleukin 1

Interleukin 1, or IL 1, otherwise known as lymphocyte-activating factor, is a macrophage-derived 12,000- to 15,000-dalton polypeptide. Isoelectric focusing of human IL 1 reveals three peaks at pI's of 5.2, 6.0 and 6.9 respectively. IL 1 can be depleted of lymphocyte-derived IL 2 by SP-Sephadex chromatography. IL 1 augments the mitogenic response of PNA- Lyt 1+ thymocytes, and promotes thymocyte helper functions and B cell antibody production. IL 1 induces stable E rosette formation and the production of lymphokines such as T cell growth factor (IL 2) by peripheral T lymphocytes. Others have shown that IL 1 or closely related factors also stimulate hypothalamic cells to induce fever; induce in vitro fibroblast growth, prostaglandin, and collagenase production; and stimulate hepatocytes to produce acute phase proteins such as serum amyloid A. Murine epidermal cells also produce a 15,000-dalton factor that is mitogenic for thymocytes and may be similar to IL 1. We have recently hybridized spleen cells from mice sensitized with partially purified human IL 1 with a myeloma cell line. Clones have been isolated that produce supernatants that partially inhibit the thymocyte proliferative response to IL 1 but not the T cell growth factor activity of IL 2. Should these hybridoma products prove to be monoclonal anti-IL 1 antibodies, they will facilitate the further purification and characterization of IL 1.