Transforming growth factor beta: possible roles in the regulation of normal and leukemic hematopoietic cell growth

We have recently demonstrated that transforming growth factor (TGF)-beta 1 and TGF-beta 2 are potent inhibitors of the growth and differentiation of murine and human hematopoietic cells. The proliferation of primary unfractionated murine bone marrow by interleukin-3 (IL-3) and human bone marrow by IL-3 or granulocyte/macrophage colony-stimulating factor (GM-CSF) was inhibited by TGF-beta 1 and TGF-beta 2, while the proliferation of murine bone marrow by GM-CSF or murine and human marrow with G-CSF was not inhibited. Mouse and human hematopoietic colony formation was differentially affected by TGF-beta 1. In particular, CFU-GM, CFU-GEMM, BFU-E, and HPP-CFC, the most immature colonies, were inhibited by TGF-beta 1, whereas the more differentiated unipotent CFU-G, CFU-M, and CFU-E were not affected. TGF-beta 1 inhibited IL-3-induced growth of murine leukemic cell lines within 24 h, after which the cells were still viable. Subsequent removal of the TGF-beta 1 results in the resumption of normal growth. TGF-beta 1 inhibited the growth of factor-dependent NFS-60 cells in a dose-dependent manner in response to IL-3, GM-CSF, G-CSF, CSF-1, IL-4, or IL-6. TGF-beta 1 inhibited the growth of a variety of murine and human myeloid leukemias, while erythroid and macrophage leukemias were insensitive. Lymphoid leukemias, whose normal cellular counterparts were markedly inhibited by TGF-beta, were also resistant to TGF-beta 1 inhibition. These leukemic cells have no detectable TGF-beta 1 receptors on their cell surface. Last, TGF-beta 1 directly inhibited the growth of isolated Thy-1-positive progenitor cells. Thus, TGF-beta may be an important modulator of normal and leukemic hematopoietic cell growth.     

IL-4, IL-10, IL-13, and TGF-beta from an altered peptide ligand-specific Th2 cell clone down-regulate adoptive transfer of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is induced in the SJL/J mouse by adoptive transfer of activated proteolipid protein peptide (PLP) 139-151-specific Th1 cells. T cells responding to altered peptide ligands (APL) of PLP, previously shown to induce Th2 differentiation and regulate disease in PLP-immunized mice, do not transfer EAE. However, the exact mechanism of disease regulation by APL-specific T cells has not been elucidated. In this report, we show that 1F1, a Th2 clone specific for an APL of PLP139-151 can prevent adoptive transfer of EAE when cocultured with PLP-encephalitogenic spleen cells (PLP-spleen). Cytokines from activated 1F1 cells were detected by hybridization of mRNA to oligonucleotide arrays (DNA chip) and by ELISA. The Th2 cytokines found to be present at the highest protein and mRNA levels were evaluated for their role in suppression of adoptive transfer of EAE from PLP-activated spleen cell cultures. Abs to individual cytokines in 1F1 PLP-spleen cocultures suggested that IL-4, IL-13, and TGF-beta played a significant role in suppressing EAE. Abs to the combination of IL-4, IL-10, IL-13, and TGF-beta completely neutralized the protective effect of 1F1. Addition of Th2 cytokines to PLP-spleen cultures showed that IL-13 and TGF-beta were each individually effective and low levels of IL-4 synergized with IL-13 to inhibit disease transfer. IL-5, IL-9, and IL-10 had little or no effect whereas GM-CSF slightly enhanced EAE. Our results demonstrate that Th2 cytokines derived from APL-specific Th2 cells can effectively down-regulate the encephalitogenic potential of PLP-spleen cells if present during their reactivation in culture.     

IL-4 inhibits the expression of high affinity IL-2 receptors on monoclonal human B cells

In the presence of anti-mu antibodies (anti-microAb), monoclonal B lymphocytes from patients suffering from B type chronic lymphocytic leukemia (B-CLL) can respond to IL-2. In contrast to the effect it exerts on normal B cells, IL-4 does not promote DNA synthesis by B-CLL lymphocytes. Rather this interleukin inhibits the response to IL-2 in all patients' cells that responded to this interleukin. We thus examined whether IL-4 would modulate the number and/or the affinity of IL-2 receptors. A 3-day activation of cells by anti-microAb induced a few hundred high affinity IL-2 receptors (HA-IL-2R) on B-CLL cell surface, as determined by Scatchard analysis. Treatment of cells with IL-4 caused a marked decrease in the number of HA-IL-2R without interfering with the binding ability of IL-2. In contrast with this profound suppressive effect, IL-4 did not down-regulate the expression of each chain, alpha and beta (p55 and p75, respectively), of the HA-IL-2R heterodimer. In fact, the expression of alpha and beta induced by anti-microAb was enhanced by IL-4. Altogether, IL-4 exerts a critical influence on the function and the configuration of HA-IL-2R without inhibiting the expression of two subunits, alpha and beta.     

Interleukin 3-specific tyrosine phosphorylation of a membrane glycoprotein of Mr 150,000 in multi-factor-dependent myeloid cell lines.

Tyrosine phosphorylation of cellular proteins induced by various hematopoietic growth factors such as interleukin 3 (IL3), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL4) was studied in several multi-factor-dependent myeloid cell lines. Among the growth factors, IL3 specifically induced rapid tyrosine phosphorylation of a membrane glycoprotein of mol. wt 150 kd (gpp150) in the IL3-dependent cell lines, IC2 and DA-1. The IL3-induced tyrosine phosphorylation of gpp150 was detected within 30 s, reached a maximum at 3 min and decreased thereafter. The concentration of IL3 required for half-maximum stimulation of gpp150 tyrosine phosphorylation with 2.5 x 10(6)/ml cells was approximately 200 pM, which is the same as the dissociation constant for 125I-labeled IL3 binding. gpp150 was constitutively phosphorylated on tyrosine residue(s) in growth factor independent variants, IC2Tr and DA-1Tr, derived from IC2 and DA-1 respectively. Neither variant synthesized IL3. The present findings suggest that tyrosine phosphorylation of gpp150 is a critical event involved in both IL3-dependent and -independent growth.     

Effect of cytokines and growth factors on the macrophage colony-stimulating factor secretion by human bone marrow stromal cells

We have investigated the effect of growth factors, inflammatory and anti-inflammatory cytokines on the macrophage colony-stimulating factor (M-CSF) secretion by cultured human bone marrow stromal cells. Their production of M-CSF cultured in serum-free medium is enhanced in a time-dependent manner in response to tumour necrosis factor (TNF-)alpha and interleukin (IL-)4 but not to IL-1, IL-3, IL-6, IL-7, IL-10, SCF, granulocyte-macrophage colony-stimulating factor (GM-CSF), G-CSF, bFGF and transforming growth factor (TGF-)beta. The co-addition of IL-4 and TNF-alpha has a greater than additive effect on the secretion of M-CSF suggesting that they act synergistically. The anti-inflammatory molecules IL-10 and TGF-beta have no effect on the TNF-alpha-induced M-CSF synthesis by marrow stromal cells. In conclusion TNF-alpha and IL-4 are potent stimulators of the M-CSF synthesis by human bone marrow stromal cells, a result of importance regarding the role of M-CSF in the proliferation/differentiation of mononuclear-phagocytic cells and the role of marrow stromal cells as regulators of marrow haematopoiesis.     

Suppression of apoptotic death in hematopoietic cells by signalling through the IL-3/GM-CSF receptors.

Interleukin 3 (IL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) exert their biological functions through acting on a specific receptor which consists of a ligand-specific alpha subunit and the shared common beta subunit. Inhibition by genistein of a subset of IL-3/GM-CSF-mediated signals, including c-myc induction, resulted in the abrogation of DNA synthesis, however, IL-3 still protected cells from apoptotic cell death. Conversely, a C-terminal truncated form of the GM-CSF receptor, which is missing a critical cytoplasmic region required for activation of the Ras/Raf-1/MAP kinase pathway, induced DNA synthesis, but failed to prevent cell death in response to GM-CSF. Consequently, cells died by apoptosis in the presence of GM-CSF, despite displaying a transient mitogenic response. However, expression of activated Ras protein complemented defective signalling through the mutant receptor and supported long-term proliferation in concert with GM-CSF. These results indicate that IL-3 and GM-CSF prevent apoptosis of hematopoietic cells by activating a signalling pathway distinct from the induction of DNA synthesis and that long-term cell proliferation requires the activation of both pathways.     

Granulocyte-macrophage colony-stimulating factor is a major macrophage fusion factor present in conditioned medium of concanavalin A-stimulated spleen cell cultures

In 1983, we reported that the conditioned medium (CM) of spleen cell cultures treated with Con A greatly induced fusion of mouse alveolar macrophages within 2 to 3 days at a very high rate of more than 80% (Proc. Natl. Acad. Sci. USA 80:5583, 1983). In the course of examining macrophage fusion factors (MFF) present in Con A-CM, we found that IL-4 induced fusion of alveolar macrophages with a time course similar to that induced by Con A-CM. However, the maximal fusion rate induced by IL-4 (4 ng/ml) was about 35%. Furthermore, the fusion induced by Con A-CM was blocked only partially by adding IL-4 antibody, indicating that there are unknown MFF other than in Con A-CM. Of several other cytokines produced by Con A-stimulated spleen cells, IL-6 (20 ng/ml), IFN-gamma (45 ng/ml) and granulocyte-macrophage (GM)-CSF (10 ng/ml) greatly potentiated the fusion induced by 4 ng/ml of IL-4. The assay of these cytokines in Con A-CM proved that it contained 0.44 +/- 0.04 ng/ml of IL-4, 1.0 +/- 0.24 ng/ml of IL-6, 9.1 +/- 0.07 ng/ml of IFN-gamma, and 11.6 +/- 1.66 ng/ml of GM-CSF. When the potentiating effects of IL-6, IFN-gamma and GM-CSF on macrophage fusion were examined in the presence of 0.4 ng/ml of IL-4, only GM-CSF increased the fusion rate to the maximal level induced by Con A-CM at its physiologic concentration (10 ng/ml). The macrophage fusion induced by Con A-CM was greatly suppressed by adding antibody against GM-CSF. GM-CSF had a biphasic effect on growth and fusion, depending on its dose levels used: 0.01 to 0.1 ng/ml increased proliferation without inducing fusion and 10 ng/ml preferentially induced fusion. There was a negative relationship between macrophage growth and fusion. IL-4 was a potent inhibitor of proliferation of macrophages induced by GM-CSF. These results clearly indicate that GM-CSF is a major MFF present in Con A-CM.     

Production of IL-10, TNF-alpha, IFN-gamma, TGF-beta1 by different populations of erythroid cells derived from human embryonal liver

It has previously been determined that erythroid cells of mice are capable of expressing such cytokines as interleukin (IL) 1 alpha and beta, IL-4, IL-6, interferon gamma (IFN-gamma), granulocyte-macrophage colony-stimulating factor (GM-CSF) and transforming growth factor beta (TGF-beta). It has been shown that glycophorin A(+) (GlA(+)) and antigen erythroblasts (AG-EB(+)) (both human erythroid cells of embryonic origin) are also capable of producing a series of cytokines such as IL-1 beta, IL-2, IL-4 and IL-6. The aim of this work was to study the capacity of erythroid cells from human embryonic liver to produce such cytokines as IFN-gamma, TGF-beta1, tumour necrosis factor alpha (TNF-alpha) and IL-10. The erythroid cells were isolated by means of antibodies specific to erythroblasts (GlA and AG-EB), as well as those from single erythroid colonies. The production level of some cytokines varies insignificantly under the action of erythropoietin (Epo) and quantitatively differs in GlA(+) and AG-EB(+) erythroid cells. Hence, the erythroid cells express IFN-gamma, TGF-beta1, TNF-alpha and IL-10. The erythroid cells could be involved through the production of these cytokines in the regulation of such processes as self-renewal, proliferation and differentiation of cells of other blood-forming sites.     

Enhancement by transforming growth factor-beta 1 (TGF-beta 1) of the proliferation of leukemic blast progenitors stimulated with IL-3.

We studied the effect of transforming growth factor-beta 1 (TGF-beta 1) on colony formation of leukemic blast progenitors from ten acute myeloblastic leukemia (AML) patients stimulated with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), interleukin-6 (IL-6), or interleukin-1 beta (IL-1 beta). These CSFs and interleukins by themselves stimulated the proliferation of leukemic blast progenitors without adding TGF-beta 1. G-CSF, GM-CSF, and IL-3 stimulated blast colony formation in nine patients, IL-6 stimulated it in five, and IL-1 beta stimulated in four. TGF-beta 1 significantly reduced blast colony formation stimulated by G-CSF, GM-CSF, or IL-6 in all patients. In contrast, TGF-beta 1 enhanced the stimulatory effect of IL-3 on blast progenitors from three cases, while in the other seven patients TGF-beta 1 reduced blast colony formation in the presence of IL-3. To study the mechanism by which TGF-beta 1 enhanced the stimulatory effect of IL-3 on blast progenitors, we carried out the following experiments in the three patients in which it occurred. First, the media conditioned by leukemic cells in the presence of TGF-beta 1 stimulated the growth of leukemic blast progenitors, but such effect was completely abolished by anti-IL-1 beta antibody. Second, the addition of IL-1 beta in the culture significantly enhanced the growth of blast progenitors stimulated with IL-3. Third, leukemic cells of the two patients studied were revealed to secrete IL-1 beta and tumor necrosis factor-alpha (TNF-alpha) constitutively; the production by leukemic cells of IL-1 beta and TNF-alpha was significantly promoted by TGF-beta 1. Furthermore, the growth enhancing effect of TGF-beta 1 in the presence of IL-3 was fully neutralized by anti-IL-1 beta antibody. These findings suggest that TGF-beta 1 stimulated the growth of blast progenitors through the production and secretion of IL-1 beta by leukemic cells.     

The network of hemopoietic regulatory proteins in myeloid cell differentiation.

There are clones of myeloid leukemic cells that can be induced to undergo terminal cell differentiation to macrophages by normal hemopoietic regulatory proteins. Induction of differentiation in two different clones of myeloid leukemic cells with interleukin 6 (IL-6) or granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in induction of mRNA for the hemopoietic regulatory proteins IL-6, GM-CSF, interleukin 1 alpha and interleukin 1 beta, tumor necrosis factor, and transforming growth factor beta 1. In one of these clones, induction of differentiation with GM-CSF was also associated with induction of mRNA for macrophage colony-stimulating factor (M-CSF) but not for the receptor for M-CSF (c-fms), whereas in the other clone, induction of differentiation with IL-6 was associated with induction of mRNA for both c-fms and M-CSF. The clones also differed in their responsiveness to these regulators. There was no induction of mRNA for granulocyte colony-stimulating factor or interleukin 3 during differentiation of either clone. The results indicate that the genes for a nearly normal network of positive and negative hemopoietic regulatory proteins are induced during differentiation of these myeloid leukemic cells and that there are leukemic clones with specific defects in this network.     

Evidence for a role of the Na+/H+ exchanger in the colony-stimulating-factor-induced ornithine decarboxylase activity and proliferation of the human cell line M-07e

The subclone M-07e, derived from the interleukin-3 (IL-3)-responsive human myeloid cell line M-07, is strictly dependent on either IL-3 or granulocyte-macrophage-colony-stimulating factor (GM-CSF) for its growth and survival. This cell line may be regarded as a candidate model to investigate the poorly understood events triggered by growth factors binding to human hemopoietic cells. Both IL-3 and GM-CSF induce in M-07e cells an increase of ornithine decarboxylase (ODC) activity, which reaches its maximum at 24-30 h and fully depends on de novo protein synthesis. The growth factors do not elicit translocation of protein kinase C to the membrane; thus a role of the kinase in ODC induction is ruled out. An amiloride-inhibitable Na+/H+ exchanger is present in the membrane of M-07e cells; its apparent Km for extracellular Na+ is 47.77 mM; and its activity is greatly enhanced when the cytoplasm is acidified. Growth-factor-evoked ODC activation and DNA synthesis are blocked in a dose- and time-dependent manner when M-07e cells are incubated with ethylisopropylamiloride, a specific inhibitor of Na+/H+ exchanger. The exchanger does not appear to be directly activated by IL-3 or GM-CSF, but its operation is strictly required for the biological effects of these growth factors on M-07e cell line.     

Foxp3 inhibits RORgammat-mediated IL-17A mRNA transcription through direct interaction with RORgammat

The cytokine, transforming growth factor-beta1 (TGF-beta1), converts naive T cells into regulatory T cells that prevent autoimmunity. However, in the presence of interleukin (IL)-6, TGF-beta1 has also been found to promote differentiation into IL-17-producing helper T (Th17) cells that are deeply involved in autoimmunity and inflammation. However, it has not been clarified how TGF-beta1 and IL-6 determine such a distinct fate. Here we found that a master regulator for Th17, retinoic acid-related orphan receptor gammat (RORgammat), was rapidly induced by TGF-beta1 regardless of the presence of IL-6. IL-6 reduced Foxp3 expression, and overexpression of Foxp3 in a T cell line resulted in a strong reduction of IL-17A expression. We have characterized the IL-17A promoter and found that RORgammat binding is sufficient for activation of the minimum promoter in the HEK 293T cells. RORgammat-mediated IL-17A promoter activation was suppressed by forced expression of Foxp3. Foxp3 directly interacted with RORgammat through exon 2 region of Foxp3. The exon 2 region and forkhead (FKH) domain of Foxp3 were necessary for the suppression of RORgammat-mediated IL-17A promoter activation. We propose that induction of Foxp3 is the mechanism for the suppression of Th17 and polarization into inducible Treg.     

Co-stimulation of T cell proliferation by transforming growth factor-beta 1.

Transforming growth factor-beta (TGF-beta) exhibits diverse regulatory roles in the immune system and has been described as a potent inhibitor of lymphocyte and hemopoietic progenitor cell growth. The present studies investigated the effects of TGF-beta 1 on murine T cell proliferation triggered through the T cell receptor/CD3 complex. In contrast to previously reported T cell growth inhibition, TGF-beta 1 costimulated splenic T cell proliferation in the presence of immobilized anti-CD3 antibody 2C11, with maximal effect at anti-CD3 concentration of 50 micrograms/ml. Although TGF-beta 1 induced a modest increase in IL-2R display, TGF-beta 1 co-stimulated proliferation was largely independent of IL-2 and/or IL-4. Anti-IL-2 and/or anti-IL-4 antibody did not significantly block the TGF-beta 1 co-stimulated T cell growth, and no IL-2 or IL-4 bioactivity was detected in TGF-beta 1 co-stimulated cultures. TGF-beta 1 did not enhance IL-2 mRNA expression beyond control levels. However, TGF-beta 1 co-stimulation caused an accelerated evolution of a memory or mature T cell population phenotype. Both CD4+ and CD8+ T cell subsets were significantly enriched for cells of the mature CD45RBloPgp-1hi phenotype, in comparison with T cells stimulated by anti-CD3 alone or with PMA, and CD8+ T cells predominated. These results thus provide initial evidence that TGF-beta 1 is capable of bifunctional T cell growth regulation, which occurs largely via an IL-2- and IL-4-independent pathway.     

Transforming growth factor-beta is a potent immunosuppressive agent that inhibits IL-1-dependent lymphocyte proliferation

Transforming growth factor-beta (TGF-beta), a product of neoplastic and hemopoietic cells, is a bifunctional regulator of the immune response. At femtomolar concentrations, TGF-beta stimulates monocyte migration, and picomolar quantities induce synthesis of monocyte growth factors, including IL-1, that may promote tissue repair by regulating fibrosis and angiogenesis. Paradoxically, TGF-beta at picomolar concentrations also blocks the ability of IL-1 to stimulate lymphocyte proliferation. At 0.01 to 1.0 ng/ml, TGF-beta 1 and its homologue, TGF-beta 2, suppress the IL-1-dependent murine thymocyte proliferation assay. TGF-beta also inhibits human peripheral blood T lymphocyte mitogenesis. Inhibition of cell division appears to occur after activation of the lymphocytes inasmuch as neither gene expression nor translation of IL-2R is suppressed. Furthermore, TGF-beta does not block synthesis of IL-2. Therefore, TGF-beta 1 and TGF-beta 2 likely act at a site distal to IL-1 to block lymphocyte DNA synthesis. These findings suggest that TGF-beta secreted in an inflammatory site may be beneficial in diminishing lymphocyte function while promoting fibrosis and tissue repair. However, TGF-beta generated by neoplastic tissues may provide a mechanism for unrestricted tumor cell growth through its selective immunosuppressive effects.     

Activation via TCR or IL-2 receptor of a CD8+ suppressor T cell clone: Effect on IL-10 production and on proliferation of the suppressor T cell

In a previous study, we established CD8⁺ suppressor T cell (Ts) clone 13G2 which produced the suppressive lymphokine, interleukin-10 (IL-10). In this study, we examined what physiological activator could induce both production of IL-10 from 13G2 and the proliferation of 13G2. Both the antigenic stimulation mimicked by the anti-CD3 antibody and the T cell growth factor interleukin-2 (IL-2) induced IL-10 production from the 13G2 clone equally well. 13G2 cells proliferated remarkably with IL-2 stimulation, while anti-CD3 only slightly induced proliferation of the clone. 13G2 cells also produced IL-10 in the presence of hydroxyurea which blocked transit of cells from G₁ to S phase. However, cycloheximide blocked the production of IL-10 from the Ts clone. The study demonstrates that both the anti-CD3 antibody and IL-2 induced IL-10 synthesis of the Ts clone equally well, and the proliferative response of Ts cells was induced more by IL-2 than by anti-CD3. IL-2 proved to be a good stimulator for Ts cells to produce suppressive lymphokine and to multiply their population.Abbreviation Ts suppressor T cell - Th helper T cell - Ag antigen - APC antigen presenting cell - IL interleukin - TCR T cell receptor - mAb monoclonal antibody     

Interleukin-6 and transforming growth factor-beta synergistically stimulate chondrosarcoma cell proliferation

This study examines the regulation of Swarm rat chondrosarcoma (SRC) cell proliferation in vitro. In serum-free cultures, SRC cells showed only transient DNA synthesis and this was increased by serum. Transforming growth factor-beta (TGF-beta) was identified as an essential serum component, since the mitogenic effect of sera was related to their TGF-beta content and neutralized by antibody to TGF-beta. Among a large panel of agents tested, TGF-beta was the only factor that stimulated proliferation in serum-free media. The TGF-beta isoforms TGF-beta 1 and TGF-beta 2 induced similar dose-dependent increases with maximal 62.5-fold stimulation at 10 ng/ml. Interleukin-6 (IL-6) was identified as a new factor that stimulated SRC proliferation. IL-6 effects were serum-dependent and their magnitude correlated with the TGF-beta content in different serum preparations. In serum-free cultures where IL-6 by itself had no detectable effect it caused up to 7.6-fold increased proliferation in the presence of small doses of TGF-beta (0.01-0.1 ng/ml). This synergy was unique, since no other factor tested synergized with IL-6 or TGF-beta. In examining potential mechanisms for this synergy it was found that TGF-beta increased IL-6 receptor expression. In summary, these results identify IL-6 as a new and TGF-beta as the most potent growth factor for chondrosarcoma cells and describe novel interactions between these factors in the regulation of cell growth.     

The direct effects of interleukin 1, interleukin 2, interferon-alpha, interferon-gamma, B-cell growth factor, and a B-cell differentiation factor on resting and activated human B cells

A wide variety of cytokines have been demonstrated to affect B-cell function. However, it is unclear which of these mediators actually exert direct effects on the B cells themselves. In the present study, the direct role of interleukin (IL) 1, IL-2, Interferon-gamma, or Interferon-alpha in human B-cell activation, proliferation, or differentiation was examined and compared with the effects of a B-cell growth factor (BCGF) or a B-cell differentiation factor (BCDF). Highly purified human B lymphocytes were separated according to size into two nonoverlapping populations. The fraction of small B cells was incubated with IL-1, IL-2, Interferon-gamma, Interferon-alpha, BCGF, or BCDF, and cell size changes, RNA synthesis, DNA synthesis, or supernatant immunoglobulin (Ig) production were measured. Neither IL-1, IL-2, Interferon-alpha, Interferon-gamma, nor the BCGF induced substantial cell size changes, RNA synthesis, DNA synthesis, or Ig production by the small fraction of B lymphocytes; however, the BCDF could directly activate a proportion of resting B lymphocytes to secrete Ig. The fraction of large B cells was also incubated with these cytokines. While neither IL-1, Interferon-alpha, nor Interferon-gamma enhanced DNA synthesis or Ig production by the fraction of large B lymphocytes, DNA synthesis was augmented 23-fold by BCGF and IgG production was increased 7-fold by BCDF. Additionally, IL-2 slightly enhanced both proliferation and differentiation of large B cells but substantially less so than BCGF and BCDF; DNA synthesis was increased 4-fold, while Ig production in the presence of IL-2 was increased by approximately 50%. Thus, the most important lymphokines modulating the function of these two fractions of tonsillar lymphocytes were a BCGF and a BCDF.