B-cell Differentiation Factor Research Articles

5362489 Use of recombinant B-cell differentiation factor for augmenting antibody production and stimulating bone marrow proliferation : Kishimoto Tadamitsu; Hirano Toshio; Matsui Hiroshi; Takahara Yoshiyuki; Akiyama Yukio; Okano Akira - Ajinomoto Co Inc; Tadamitsu Kishimo

5362489 Use of recombinant B-cell differentiation factor for augmenting antibody production and stimulating bone marrow proliferation : Kishimoto Tadamitsu; Hirano Toshio; Matsui Hiroshi; Takahara Yoshiyuki; Akiyama Yukio; Okano Akira - Ajinomoto Co Inc; Tadamitsu Kishimo

5362489 Use of recombinant B-cell differentiation factor for augmenting antibody production and stimulating bone marrow proliferation

5362489 Use of recombinant B-cell differentiation factor for augmenting antibody production and stimulating bone marrow proliferation

Identification of CD36 as the first gene dependent on the B-cell differentiation factor Oct-2.

The Oct-2 transcription factor is expressed predominantly in B lymphocytes and has been shown previously to be important for the terminal phase of B-cell differentiation in mice. A number of genes specifically expressed in B cells contain Oct-2-binding sites in their regulatory regions. However, the analysis of expression levels of these genes in Oct-2-deficient B cells revealed that they were unaffected. Hence, there were no genes known that critically depend on Oct-2 for their expression. To understand the molecular basis for the Oct-2 effect on B-cell development, we searched for Oct-2 target genes by subtractive cDNA cloning. We show here that expression of the murine CD36 gene in B cells and macrophages requires a functional Oct-2 protein. Nuclear run-on experiments demonstrate that this gene is regulated transcriptionally by Oct-2. Moreover, CD36 levels correlated with the levels of Oct-2 expression in several mouse B-cell and macrophage cell lines. Finally, compared to wild-type and heterozygous mice, CD36 mRNA levels were markedly reduced in spleens and B-cell-enriched splenocyte fractions from oct-2-/- mice. The data identify CD36 as the first target gene critically dependent on Oct-2 for its expression. Because CD36 expression is also dependent on Oct-2 in vivo, it is a candidate gene through which Oct-2 could affect B-cell differentiation.

B Cell Differentiation Factor-Induced B Cell Maturation: Regulation via Reduction in cAMP

We have previously described a novel human B cell differentiation factor (BCDF), 446-BCDF, that is distinct biochemically and functionally from other cytokines. Since signal transduction pathways involved in human B cell differentiation have been incompletely studied and are poorly understood, we assessed the effects of 446-BCDF on various intracellular second messenger systems. After exposure of B cells to 446-BCDF, intracellular cAMP concentration started to decrease at 5 min and was significantly lower at 30 min and reached the lowest level at 4 hr. In most cases, cAMP concentrations returned toward baseline by 24 hr. A cAMP analog (dibutyryl cAMP), a stimulator of adenyl cyclase (forskolin), and phosphodiesterase inhibitors (aminophylline and IBMX) which inhibited the 446-BCDF-induced decrease in intracellular cAMP, inhibited 446-BCDF-induced B cell differentiation, suggesting that the fall in intracellular cAMP was a critical event in this process. To understand the mechanism involved in the reduction of cAMP, B cells were treated with pertussis toxin (PTX), a G i protein inhibitor. Pertussis toxin blocked 446-BCDF-induced B cell differentiation as well, suggesting that 446-BCDF may function by stimulation of a G i-linked receptor resulting in the inhibition of adenylate cyclase with a consequent reduction in cAMP. Other cytokines known to promote Ig secretion (IL2 and IL6) also caused a reduction in cAMP, suggesting that this pathway may be generally important in B cell differentiation. Taken together, these data suggest that at least one pathway of terminal maturation in B cells may involve the reduction of intracellular cAMP.

Interleukin-6 production in B-cell neoplasias and Castleman's disease: Evidence for an additional paracrine loop

Functioning as a B-cell growth and differentiation factor, interleukin-6 (IL-6) may play an important role in the pathophysiology of B-cell tumors. The capacity for IL-6 secretion was evaluated in 58 patients with various B-cell leukemias/lymphomas and in four patients with Castleman's disease (CMD). Cell populations from various sites including peripheral blood, bone marrow, lymph nodes, and osteolytic bone lesions were cultured and tested for spontaneous or IL-1 beta/TNF alpha-induced IL-6 production in a sensitive bioassay. No significant IL-6 levels were released by the tumor cells in any of the B-cell leukemias or lymphomas tested, including hairy cell leukemia (HCL) and B-cell chronic lymphocytic leukemia (B-CLL). In contrast, purified malignant plasma cells were found to secrete IL-6, strengthening the idea that an autocrine pathway for growth regulation in multiple myeloma (MM) exists. For the first time, in several patients with CMD, peripheral blood cells were shown to produce extremely high levels of IL-6, the pathogenetic significance of which remains to be elucidated. However, similar observations were very occasionally made in MM patients. Therapy with corticosteroids strongly inhibited this IL-6 production. These data provide evidence for autocrine and possibly an additional paracrine regulatory loop in plasma cell neoplasias and CMD.

Production of factors with B-cell growth and differentiation activities by peripheral blood mononuclear cells from patients with hypogammaglobulinemia

Background: The maturation of normal B lymphocytes proceeds through a growth phase and a differentiation phase. These two phases appear to be under the influence of mediators released by immune cells, B-cell growth factor(s), which induce proliferation of B cells; and B-cell differentiation factor(s), which induce B-cell differentiation. Methods: We analyzed the ability of peripheral blood mononuclear cells from patients with hypogammaglobulinemia to produce B-cell growth factor and B-cell differentiation factor activity in comparison with normal peripheral blood mononuclear cells. Results: Of 27 patients tested, 26 had normal production of B-cell growth factor activity. A quantitative but not absolute defect in B-cell growth factor production was demonstrable in one boy with hypogammaglobulinemia. Interleukin-2 and interleukin-4 levels, as determined antigenically in these supematants, had a similar distribution pattern from patients' or from control peripheral blood mononuclear cells; that is, undetectable levels of interleukin-2 were produced by cells from 4 of 16 patients tested and from 4 of 13 control subjects, and undetectable levels of interleukin-4 produced by cells from 6 of 16 patients and 4 of 13 control subjects. B-cell differentiation factor activity was absent in only one child tested but present in all other patients. Two patients had quantitatively low secretion of B-cell differentiation factor, but all others were within normal range. The two patients with quantitatively depressed B-cell differentiation factor activity had normal levels of B-cell growth factor activity, interleukin-2, and interleukin-4 produced from their cells. Conclusion: Peripheral blood mononuclear cells from the majority of patients with hypogammaglobulinemia appear to have the capacity to produce B-cell growth factors and B-cell differentiation factor activity in vitro.

Interleukin-5 and Its Receptor System: Implications in the Immune System and Inflammation

Publisher Summary The chapter summarizes advances in interleukin-5 (IL-5) and IL-soluble receptor (IL-SR) research in the study of structure, physiologic functions, and the unique modes of receptor-mediated signaling. The chapter also discusses the pathophysiology of aberrant expression of IL-5 and its receptor. Helper T cells recognize antigenic peptide in the context of class IL1 major histocompatibility complex (MHC) molecules on accessory cells and/or B cells and secrete several soluble factors, including IL-4, IL-5, and IL-6, that can induce B-cell growth and the maturation of B cells. Mouse IL-5 (mIL-5) is a glycoprotein induced in T cells after stimulation with an antigen, such as Mycobacterium tuberculosis or Toxocara canis, and in mast cells upon stimulation with allergen/IgE complex or calcium ionophores. The action of IL-5 in responsive cells is the molecular mechanism of signal transduction cascade after IL-5 binding to the functional IL-5 receptor (IL-5R). The IL-5 signals can be transduced through the high-affinity IL-5R that consists of two different polypeptide subunits: α and β. The cDNAs encoding both α - and β -subunits for mIL-5R have been isolated; the α -subunit was found to be a 60 kDa (p60) protein and the β-subunit (a 130-kDa protein, p130) was identified as the protein identical to the β-subunit for mIL-3R and mGM-CSFR, which can convert the low affinity mILSRα into a high-affinity receptor. The study of mIL-5 originated from the search for the B-cell differentiation factor that induces antigen-primed B cells to differentiate into antigen-specific antibody-producing cells or the proliferation of BCLl B-cell tumor cells.

The accessory gene regulator (agr) controls Staphylococcus aureus virulence in a murine arthritis model

We have studied the role of the accessory gene regulator (agr) of Staphylococcus aureus as a virulence determinant in the pathogenesis of septic arthritis. At least 15 genes coding for potential virulence factors in Staphylococcus aureus are regulated by a putative multicomponent signal transduction system encoded by the agr/hld locus. agr and hld mutants show a decreased synthesis of extracellular toxins and enzymes, such as alpha-, beta-, and delta-hemolysin, leucocidin, lipase, hyaluronate lyase, and proteases, and at the same time an increased synthesis of coagulase and protein A as compared with the wild-type counterpart. We have used a recently described murine model of S. aureus-induced arthritis to study the virulence of S. aureus 8325-4 and two agr/hld mutants derived from it. Sixty percent of the mice injected with the wild-type strain developed arthritis, whereas agrA and hld mutants displayed joint involvement in only 10 and 30%, respectively. In addition, 40% of the mice inoculated with the wild-type strain displayed an erosive arthropathy; such changes were not detectable at all in mice inoculated with the agrA mutant. Serum levels of interleukin-6, a potent B-cell differentiation factor, were significantly higher (P < 0.001) in the mice inoculated with the wild-type strain than in those inoculated with the agrA mutant counterpart. Overall, our results suggest that the agr system of S. aureus is an important virulence determinant in the induction and progression of septic arthritis in mice.

Interleukin-5 (IL-5) and IL-6 define two molecularly distinct pathways of B-cell differentiation.

Interleukin-5 (IL-5) and IL-6 have both been reported to act as B-cell differentiation factors by stimulating activated B cells to secrete antibody. However, it has not been possible to directly compare the effects of these two lymphokines because of the lack of a suitable B-cell line capable of responding to both. We have identified a clonal, inducible B-cell lymphoma, CH12, that has this property. Both IL-5 and IL-6 can independently stimulate increases in steady-state levels of immunoglobulin and J-chain mRNA and proteins, and they both induce the differentiation of CH12 into high-rate antibody-secreting cells. Nevertheless, there are significant differences in the activities of these two lymphokines. First, while IL-6 acts only as a differentiation factor, IL-5 also augments the proliferation of CH12 cells. Second, the differentiation stimulated by IL-5 but not by IL-6 is partially inhibited by IL-4. Inhibition of IL-5-induced differentiation was not at the level of IL-5 receptor expression, since IL-4 did not inhibit IL-5-induced proliferation. Third, IL-5 but not IL-6 stimulated increased mouse mammary tumor proviral gene expression in CH12 cells. These results demonstrate that while both IL-5 and IL-6 may act as differentiation factors for B cells, they induce differentiation by using at least partially distinct molecular pathways. Our results also establish that B cells characteristic of a single stage of development can independently respond to IL-4, IL-5, and IL-6.

Interleukin-5 (IL-5) and IL-6 define two molecularly distinct pathways of B-cell differentiation.

Interleukin-5 (IL-5) and IL-6 have both been reported to act as B-cell differentiation factors by stimulating activated B cells to secrete antibody. However, it has not been possible to directly compare the effects of these two lymphokines because of the lack of a suitable B-cell line capable of responding to both. We have identified a clonal, inducible B-cell lymphoma, CH12, that has this property. Both IL-5 and IL-6 can independently stimulate increases in steady-state levels of immunoglobulin and J-chain mRNA and proteins, and they both induce the differentiation of CH12 into high-rate antibody-secreting cells. Nevertheless, there are significant differences in the activities of these two lymphokines. First, while IL-6 acts only as a differentiation factor, IL-5 also augments the proliferation of CH12 cells. Second, the differentiation stimulated by IL-5 but not by IL-6 is partially inhibited by IL-4. Inhibition of IL-5-induced differentiation was not at the level of IL-5 receptor expression, since IL-4 did not inhibit IL-5-induced proliferation. Third, IL-5 but not IL-6 stimulated increased mouse mammary tumor proviral gene expression in CH12 cells. These results demonstrate that while both IL-5 and IL-6 may act as differentiation factors for B cells, they induce differentiation by using at least partially distinct molecular pathways. Our results also establish that B cells characteristic of a single stage of development can independently respond to IL-4, IL-5, and IL-6.

Peripheral T-cell lymphoma with unique immunologic features.

The autologous mixed lymphocyte reaction (AMLR) is an important immunoregulatory phenomenon in human immune disorders. The authors have determined the phenotype and assessed the response of malignant lymph node T-cells, from histologically and immunologically proven cases of peripheral T-cell lymphoma, in AMLR and allogeneic mixed lymphocyte reaction (MLR) and studied the secretion of lymphokines. The proliferative response, tritiated 3H-thymidine incorporation assay, was used to determine the AMLR and allogeneic MLR of the responding T-cells. An interleukin-2 (IL-2)-dependent T-cell line (CTLL) was used for the production of IL-2 by phytohemagglutinin-stimulated T-cells in a cytotoxic assay. B-cell growth and differentiation factor activity of T-cells was studied by enzyme-linked immunosorbent assay. The AMLR of malignant lymph node T-cells was increased characteristically in 12 of the 14 lymphoma cases studied; however, that of the blood T-cells was decreased. The allogeneic MLR of the malignant lymph node T-cells and blood-purified T-cells of the eight cases investigated was decreased. Expression or deficiency of CD2 and CD3 antigens on malignant T-cells did not show any difference in the AMLR assay. This study demonstrates an important tendency of malignant T-cells from patients with peripheral T-cell lymphoma to proliferate in AMLR. The highly augmented AMLR but deficient allogeneic MLR observed in these malignant T-cells indicate that autologous recognitive events may play an important role in the immunopathogenesis of this human disease.

Cytokine and inflammation: role of IL-5 and its receptor system in inflammation

The inflammatory response is mediated by various cytokines. IL-5 is one of the inflammatory cytokines. The study of IL-5 has its origins in the search for one of the B-cell differentiation factors, named T-cell-replacing factor (TRF), that induces antigen-stimulated B cells to differentiate into antibody-forming cells. Eosinophil-differentiation factor, EDF, is a factor produced by thoracic duct lymphocytes of parasite-infected rats. cDNA cloning and mAb against IL-5 enable us to identify this molecule as a cytokine (TRF/EDF) that has pleiotropic activity on various target cells besides B cells and eosinophils. The pleiotropic activity of IL-5 is directly dependent on the initial binding to the IL-5 receptor (IL-5R) on the target cell surface. IL-5 transduces its signals through high affinity IL-5R which is constructed by two distinct polypeptides, alpha and beta. IL-5R alpha binds IL-5 with low affinity and associates with the beta chain which can convert low affinity IL-5R to high affinity IL-5R. IL-5R beta that does not bind IL-5 by itself is essential for the IL-5 signaling and is shared among IL-5R, IL-3R, and GM-CSFR. These results imply why IL-5, IL-3, and GM-CSF are eosinophylopoietin. The truncated IL-5R alpha and IL-5R beta complexes can not transduce IL-5 signals, although they bound IL-5 with high affinity, suggesting that IL-5-specific signaling may be transduced through IL-5R alpha.

Cytokines in the Vitreous of Patients With Proliferative Diabetic Retinopathy

Sixteen vitreous and paired serum samples from 13 patients with proliferative diabetic retinopathy, vitreous samples from seven cadaveric control subjects, and aqueous humor samples from 15 normal control subjects were assayed for the cytokines interleukin-1, tumor necrosis factor-alpha, interleukin-6, and interferon-gamma. Interleukin-6 was detected in 15 of 16 vitreous samples (94%) from diabetic patients, but it was not detected in any of the aqueous humor samples. Vitreous interleukin-6 levels positively correlated with ocular disease activity. Interleukin-1 was detected in seven of 16 vitreous samples (44%) and in four of ten aqueous humor samples (40%), whereas tumor necrosis factor-alpha and interferon-gamma were never detected in vitreous or aqueous fluid. Serum samples from diabetic patients and control subjects contained comparable low levels of interleukin-6. Interleukin-1, tumor necrosis factor-alpha, and interferon-gamma were not found in any of the sera. Because interleukin-6 can function as B-cell differentiation factor, this cytokine may have a role in immunoglobulin deposition in the ocular tissues and in the immunopathologic characteristics of proliferative retinopathy.

T-cell receptor α/β chain-CD3 protein complex defect in systemic lupus erythematosus: T-cell function

We describe the first case of systemic lupus erythematosus (SLE) in which peripheral blood T cells were deficient in cell surface expression of T-cell receptor α/β chain (TcRαβ) and the CD3 protein. Because of the uncommon phenotype and because of the notion that coexpression of TcRαβ and CD3 is essential for antigen-specific T-cell function, in vitro functional assays were performed, showing a highly decreased proliferative response to anti-CD3 antibody and other T-cell mitogens, deficient interleulkin-2 (IL-2) secretion, and impaired function to respond in autologous and allogeneic mixed lymphocyte reactions. However, the helper-inducer function of T cells was unaffected by deficient expression of the TcRαβ/CD3 protein complex. The relative increase of CD4+ CDw29+ helper-inducer subsets in T cells accounted for elevated secretion of two terminal B-cell stimulating factors, B-cell growth factor (BCGF) and B-cell differentiation factor (BCDF). Hence, our results suggest that the regulation of secretion of lymphokines, IL-2, and BCGF and BCDF is independently controlled in T cells, and this case illustrates the pathologic sequelae of a unique defect in T cells characteristic of SLE.

Increased Spontaneous and Lymphokine–Conditioned Iga and Igg Synthesis by B Cells From Alcoholic Cirrhotic Patients

Immunoglobulin secretion by B lymphocytes is a complex process in which lymphokines secreted by T lymphocytes play an important regulatory role. Increased serum levels of IgA and IgG have been characteristically detected in patients with alcoholic cirrhosis. We have studied the functional alterations of T and B lymphocytes implicated in the physiopathology of this common immunoglobulin abnormality. After activation with phytohemagglutinin, purified T cells from alcoholic cirrhotic patients showed significantly enhanced secretion of B-cell differentiation factors for IgG and IgA with respect to those secreted by T cells from healthy controls (p less than 0.05). Simultaneously, normal secretion of B-cell differentiation factor for IgM was demonstrated in T lymphocytes from these patients. The pattern of secretion of the lymphokines involved in the regulation of the B-cell differentiation pathway found in alcoholic cirrhotic patients was different from that of the primary biliary cirrhotic patients studied. Purified B cells from patients with alcoholic cirrhosis secreted significantly higher amounts of IgA and IgG than did those found in healthy controls, both spontaneously (p less than 0.05) and after sequential activation with immunoglobulin ligands (Staphylococcus aureus Cowan I) and a standard B-cell differentiation factor preparation (p less than 0.05). By contrast, the IgM secretion and regulatory pathway were normal in alcoholic cirrhotic patients. These results support a physiopathological explanation for the characteristic hyperimmunoglobulinemia found in patients with alcoholic cirrhosis.

Gamma delta T cells and the immune response in visceral leishmaniasis.

Visceral leishmaniasis (VL) caused by Leishmania donovani, a protozoan parasite, is a disease of high morbidity associated with hepatosplenomegaly, hypergammaglobulinemia, fever and death. One of the immunological hallmarks of VL is a remarkable increase in serum immunoglobulin levels as a result of polyclonal B cell activation. This study demonstrated that T lymphocytes expressing the T cell receptors (TcR) gamma delta in association with CD3 molecules are increased in circulation of patients with VL. A large proportions of TcR gamma delta-bearing T cells had CD4+ CD8- phenotype, and expressed CD25, CD38, CD71 and HLA-DR activation antigens. Furthermore, we demonstrated wide functional differences in TcR gamma delta and TcR alpha beta T cells in their proliferative response, secretion of interleukin-2 (IL-2), B cell growth factor (BCGF) and B cell differentiation factor (BCDF). It was of interest that the TcR gamma delta T cells from patients with VL could be expanded by in vitro culture with human recombinant IL-2. Although these TcR gamma delta T cells secreted diminished levels of IL-2, they produced highly augmented levels of both BCGF and BCDF, suggesting that secretion of these lymphokines in these T cell subsets is regulated independently. The relative increases in the CD4+ CDw29+ TcR gamma delta T cell subsets and their secretion of highly elevated levels of BCGF and BCDF largely accounted for the humoral immune system abnormality and hypergammaglobulinemia found in this disease. These observations may help to explain that TcR gamma delta T cells might be functional in vivo and are involved in immunological mechanisms of pathogenesis in VL.

T‐cell chronic lymphocytic leukemia: T‐cell function and lymphokine secretion

The leukemic T-cells of the six patients with T-cell chronic lymphocytic leukemia (T-CLL), four with CD4 and CD45R-positive (CD4+ CD45R*) T-CLL and two with CD8 and CD45R-positive (CD8+ CD45R+) T-CLL phenotype were studied for detailed immunologic phenotypic and functional characteristics. The levels of soluble interleukin-2 receptors were elevated significantly in the serum of all four patients with CD4+ CD45R+ T-CLL. Moreover, the CD4+ CD45R+ T-CLL patients' T-cells, after in vitro stimulation with phytohemagglutinin and concanavalin A, expressed elevated percentages of interleukin-2 receptors on cells and secreted high interleukin-2 activity. The B-cell growth factor (BCGF) activity from three patients with CD4+ CD45R+ T-CLL was enhanced, but B-cell differentiation factor (BCDF) activity of the all T-CLL patients was decreased. Reduced BCGF and BCDF activity of the leukemic T-cells was one possible mechanism of hypogammaglobulinemia detected in two patients with T-CLL. All T-CLL patients' leukemic T-cells had diminished immunoregulatory functional activity in allogeneic mixed lymphocyte reactions. These observations suggest that leukemic T-cells from T-CLL patients have many immunologic functional defects that may be important in their proliferative potential.

Selective IgM deficiency: functional assessment of peripheral blood lymphocytes in vitro.

The functional aspects of the peripheral blood lymphocytes from 6 patients with primary selective IgM deficiency (sIgMD) were analyzed to elucidate its pathogenesis. The surface IgM positive B cells were present at almost the same percentage as in controls, but the percentage of cluster of differentiation (CD)4+ T cells was higher and that of CD8+ T cells was low. The patient B cells showed a significantly lower proliferative response to Staphylococcus aureus Cowan strain I (SAC) than control B cells and did not produce a significant amount of IgM when co-cultured with control T cells. Interestingly, mitomycin C (MMC)-treated patient T cells induced a greater amount of IgM production by control B cells. In addition, patient B cells treated with SAC and B cell differentiation factors (BCDF) failed to secrete IgM. These results suggest that the pathogenesis of sIgMD may be mainly due to an intrinsic defect in B cell maturation.

Cytokines regulating human B cell growth and differentiation

Utilizing a model system of anti-CD3-stimulated T cells, we have identified a potent B cell differentiation factor (BCDF) in the supernatant of these cells. This factor, 446-BCDF, appears to act on SAC-activated B cells inducing a 10- to 100-fold increase in Ig secretion. 446-BCDF has an apparent MW of 32 kDa and a pI of 6.0. Its activity cannot be inhibited by an anti-IL-6 antiserum, and activity is enhanced after passage over an anti-IL-6 affinity column. 446-BCDF activity is detected in the 50 mM salt fraction eluted from a Mono Q column. This 50 mM fraction has the only activity detected after passage over an anti-IL-6 affinity column and migrates with an apparent pI of 6.0. Taken together these data suggest that 446-BCDF is a unique potent polyclonal human BCDF which may be a predominant factor regulating terminal B cell differentiation.

Humoral immunodeficiency in t-cell chronic lymphocytic leukemia. An immunologic assessment

The humoral antibody immunodeficiency in two patients with T-cell chronic lymphocytic leukemia (T-CLL) appeared to be the result of immunoregulatory abnormalities in the leukemic T-cell populations. Both patients had CD4+ CD45R+ "virgin" or suppressor-inducer T-CLL, but Patient 1 had hypogammaglobulinemia and Patient 2, immunoglobulin (Ig) M hypergammaglobulinemia. Although, CD25+ interleukin-2 (IL-2) receptors were present on leukemic T-cells of both patient, OKT9+ (CD71) transferrin receptors and OKT10 (CD38) activation antigens were found only on Patient 2's cells. Highly elevated amounts of IL-2 was secreted from phytohemagglutinin-stimulated and concanavalin A-stimulated T-cells in both patients. In Patient 1 with hypogammaglobulinemia, immune defects involve T-cells, first an intense suppressor activity on B-cell-induced IgM and IgG synthesis and, second, deficient production of B-cell growth factor (BCGF) and B-cell differentiation factor (BCDF). In Patient 2, highly elevated BCGF and IgM-specific BCDF was secreted by T-cells, a mechanism leading to IgM hypergammaglobulinemia in this patient. These studies stress the importance of BCGF and BCDF activity of leukemic T-cells in humoral antibody immunodeficiency disorders in T-CLL cases.