Development of a human T-cell hybridoma secreting separate B-cell growth and differentiation factors.

A cloned human T-cell hybridoma (7D5) secreting B-cell growth factor (BCGF) and B-cell differentiation factor (BCDF) was established. Supernatant from this hybrid was capable of maintaining proliferation in anti-IgM-activated normal human B cells. In addition, the hybridoma supernatant induced differentiation and antibody secretion in Staphylococcus aureus Cowan I-stimulated B cells. No interleukin 2 was present in supernatant from this hybridoma. Molecular size of the hybridoma-derived BCGF and BCDF was determined by gel filtration chromatography. BCGF activity was present in the 20-kDa fractions, and BCDF activity eluted in the 30- to 35-kDa fractions. The isoelectric points of the factors, determined by chromatofocusing, were 6.6 for BCGF and 5.9 for BCDF. Finally, absorption experiments were performed using specific target cells. Phytohemagglutinin-stimulated T-cell blasts did not remove either BCGF or BCDF activity. Anti-IgM-activated B cells absorbed BCGF but not BCDF. In contrast, CESS cells removed BCDF but not BCGF. Thus, a human T-cell hybridoma secreting two distinct B-cell lymphokines was developed. Further immunochemical and functional studies of these immunoregulatory molecules should greatly enhance our understanding of the regulation of human B-cell function in normal and disease states.     

Proliferation and differentiation of single hapten-specific B lymphocytes is promoted by T-cell factor(s) distinct from T-cell growth factor.

Hapten-specific B lymphocytes reactive to fluorescein were prepared from mouse spleen, placed singly in 10-microliters culture wells, and stimulated with fluorescein-polymerized flagellin in the presence of conditioned media (CM) from various concanavalin A-stimulated cloned T-cell tumors or hybridomas. Antigen plus appropriate CM triggered 5-9% of the B cells into both clonal proliferation and differentiation into antibody-forming cells. Antigen alone stimulated 0.5-0.8% of B cells and CM alone stimulated less than 0.1%. This bioactivity was termed B-cell growth and differentiation factor(s) (BGDF). Four CM rich in T-cell growth factor (TCGF)--namely, CM from spleen and the lines EL4, T6, and 123--contained BGDF. The lines T19.1 and WEHI-3 lacked BGDF and TCGF. Four lines of evidence suggested that BGDF and TCGF were distinct molecules. First, the BGDF/TCGF ratios in the various CM varied. Second, on gel filtration, TCGF eluted as a sharp peak corresponding to a Mr of about 35,000, whereas BGDF eluted over a range corresponding to a Mr of 25,000-60,000. Third, the activity of TCGF in EL4-CM was markedly reduced by treatment with guanidine HCl while BGDF activity was not. Fourth, BGDF showed more heterogeneity than TCGF on hydrophobic chromatography. All CM or fractions active in promoting B-cell division also promoted differentiation to antibody-forming cells. These results provide unequivocal evidence that antigen and a T-cell product can synergize to directly activate a single B lymphocyte.     

Characterization of the human receptor for T-cell growth factor.

Anti-Tac monoclonal antibody has been identified as a putative antibody against the receptor for T-cell growth factor (TCGF). We now show that: (i) TCGF blocks 85% of 3H-labeled anti-Tac binding to phytohemagglutinin-activated lymphoblasts and (ii) both anti-Tac and anti-TCGF immunoprecipitate a protein band that appears to represent TCGF crosslinked to its receptor on HUT-102B2 cells. In HUT-102B2 cells, the TCGF receptor is a Mr 50,000 glycoprotein with internal disulfide bond(s) and a pI of 5.5-6.0, and it represents approximately equal to 0.05% of total cellular de novo protein synthesis. It contains a peptide of Mr 33,000 that is processed to a mature form that includes N-linked and O-linked sugars and sialic acid.     

B-cell growth factor receptor expression and B-cell growth factor response of leukemic B cell precursors and B lineage lymphoid progenitor cells

The purpose of this study was to analyze the expression of B cell growth factor (BCGF) receptors and to elucidate the biologic effects of biochemically purified natural BCGF at the B cell precursor stage of human B lineage lymphoid differentiation. The specific binding of radioiodinated high-mol-wt BCGF (125I-HMW-BCGF) and low-molecular-wt BCGF (125I-LMW-BCGF) to fresh marrow blasts from B cell precursor acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated BCGF molecules bound per blast ranged from undetectable to 24.3 X 10(3) for HMW-BCGF, and from 11.5 X 10(3) to 457.8 X 10(3) for LMW-BCGF. In 3H-TdR incorporation assays, 75% of cases showed a significant response to LMW-BCGF with a median stimulation index of 9.3. By comparison, only 33% of cases showed a significant response to HMW-BCGF with a median stimulation index of 2.4. Subsequently, B cell precursor colony assays were performed to assess and compare the biologic effects of BCGF on leukemic B lineage lymphoid progenitor cells. Among 28 cases studied, 57% responded to both HMW-BCGF and LMW-BCGF, 21% responded only to LMW-BCGF, and the remaining cases showed no proliferative response to either growth factor. The response patterns of virtually pure populations of FACS- sorted leukemic B cell precursors were essentially identical to the proliferative responses of unsorted leukemic B-cell precursors. Synergistic effects between HMW-BCGF and LMW-BCGF were observed in 80% of the cases that responded to both. The numbers of cell-bound radioiodinated BCGF molecules, the stimulation indices, as well as the number of B cell precursor colonies in BCGF-stimulated cultures showed a marked interpatient variation. Patients with structural chromosomal abnormalities (SCAs) involving 12p11-13 or patients with a Philadelphia chromosome showed a greater HMW-BCGF response at the level of leukemic progenitor cells than did other patients (P = .02). The LMW-BCGF response was significantly greater for patients with SCA than for patients without SCA (P = .04). The response of leukemic progenitor cells to HMW-BCGF or LMW-BCGF did not correlate with sex, age, disease status, FAB morphology, WBC at diagnosis, or immunophenotype. To our knowledge, this study represents the first detailed analyses of BCGF receptor expression and BCGF effects in B cell precursor ALL. The data presented provide direct evidence for the expression of functional receptors for both HMW-BCGF and LMW-BCGF in B cell precursor ALL.     

Purification and some characteristics of human T-cell growth factor from phytohemagglutinin-stimulated lymphocyte-conditioned media.

Human T-cell growth factor (TCGF), a mitogenic protein that appears in the media of cultured lymphocytes after phytohemagglutinin-stimulation, has been purified more than 400-fold from serum-free conditioned media by using a sequence of ion exchange chromatography and gel filtration. The purified growth factor elutes as a broad peak from DEAE-Sepharose, focuses diffusely at a pH of about 6.8 on isoelectric focusing (suggesting heterogeneity in electrical charge), has an estimated molecular weight of approximately 23,000 as judged by gel filtration (12,000-13,000 on Na-DodSO4/polyacrylamide gel electrophoresis), is resistant to DNase and RNase, is degraded by trypsin, and does not adhere to any of several lectin-Sepharoses. These characteristics indicate that it is nonglycosylated and protein in nature. The activity of the factor determined by cell counts or [3H]thymidine incorporation in human T lymphoblasts, is stable at room temperature in crude conditioned media, but the partially purified factor requires the addition of albumin or polyethylene glycol to maintain stability. Unlike the crude conditioned media, the purified factor lacks colony-stimulating activity and, unlike lectins, antigens, and crude conditioned media, it does not initiate blastogenesis in peripheral blood lymphocytes but is a selective mitogen for T cells that have undergone blast transformation secondary to exposure to a lectin or antigen. This indicates that the factor is a second signal in the T-cell immune response. The partially purified factor has been used to selectively grow several human T-cell lines, including cells that are cytotoxic to a variety of target cells.     

T-cell-dependent B-cell stimulation is H-2 restricted and antigen dependent only at the resting B-cell level.

Cloned lines of helper thymus-derived (T) cells produce help for bone marrow-derived (B) cell growth and Ig secretion in the presence of histocompatible adherent cells and of specific antigen. This help stimulates histocompatible as well as histoincompatible B-cell blasts polyclonally. Thus, neither antigen nor histocompatibility, but antigen-unspecific factor(s) for growth and Ig secretion are required to stimulate a B-cell blast through the next round of division. On the other hand, only histocompatible, resting, small B cells, and only those binding their specific antigen, can be stimulated by antigen-activated T-cell help to initiate growth and Ig secretion. The preference of the resting B cells for such collaboration with T-cell help is mapped to the K end of the H-2 histocompatibility locus, and probably constitutes the antigen expressed on B cells by the immune response (I) region. It appears that a resting B cell is excited by the binding of specific antigen to surface Ig and by the interaction of its surface Ia antigen with helper T cells. After this dual recognition the excited B cell can be stimulated by the antigen-unspecific factor(s) generated by the interaction of helper T-cells, adherent cells, and antigen to initiate replication.     

Purification and NH2-terminal amino acid sequence of a T-cell-derived lymphokine with growth factor activity for B-cell hybridomas.

A T-cell-derived lymphokine was identified by its ability to support the growth of a subset of B-cell hybridomas. Hybrids that failed to survive in the absence of this molecule represented a major proportion of rat-mouse hybridomas but were very rare among mouse-mouse B-cell hybrids. Stable factor-dependent B-cell hybridomas were used to monitor the purification of the growth factor from the supernatant of a clonotypically stimulated mouse helper T-cell clone. Sequential fractionation using gel filtration, anion-exchange chromatography, and reversed-phase HPLC resolved the factor from other B-cell growth factors and yielded a single-chain protein characterized by a major charge (pI = 5-7) and molecular mass (22- to 29-kDa) heterogeneity, probably due to variations in glycosylation. The NH2-terminal amino acid sequence of this protein, which is active on B-cell hybridomas in the 0.1 pM range, showed no significant homology with that of known lymphokines. Because the purified factor also supported the growth and survival in vitro of murine plasmacytomas (to be published elsewhere), it was provisionally designated interleukin-HP1 (where H stands for hybridoma and P stands for plasmacytoma).     

Establishment and characterization of human B-cell lymphoma cell lines using B-cell growth factor

B-cell non-Hodgkin's lymphomas (NHL-B) have been difficult to establish in long-term cell culture using standard techniques. We report the establishment of five representative cell lines from high grade NHL-B using B-cell growth factor (BCGF). The five NHL-B cell lines display the morphologic, immunophenotypic, genotypic, and biologic characteristics of the lymphoma cells present in the original diagnostic specimen. The cell lines showed at least a sevenfold dose-dependent increase in proliferation in vitro over background in the presence of BCGF. Other putative B-cell growth-stimulating cytokines showed no significant proliferative activity or were inhibitory in some cases. NHL-B cell lines secreted growth factor(s) into culture supernatants that mediated at least a fivefold dose-dependent increase in cell proliferation in autochthonous lymphoma cells and a 10-fold or greater stimulation in growth factor-dependent normal B cell lines in vitro. The cell lines show monoclonal rearrangements of IgH genes and nonrandom chromosomal abnormalities characteristic of NHL-B, while the expression of Epstein-Barr virus associated antigen (EBNA-I) is present in two of the five cell lines. The studies show that lineage-specific growth factors may be used to establish neoplastic B cell lines in vitro, which are important experimental systems for cellular and molecular studies in the NHL-B.     

Interleukin 4 (B-cell growth factor II/eosinophil differentiation factor) is a mitogen and differentiation factor for preactivated murine B lymphocytes.

Recently we described a murine T-cell hybrid that produces activities that promote the differentiation of eosinophils (eosinophil differentiation factor) and cause proliferation of the BCL1 B-cell lymphoma (B-cell growth factor II activity). Both activities appear to be associated with the same molecule, which has therefore been termed interleukin 4. The hybrid does not produce any other known lymphokines. We now find that purified interleukin 4 has no effects on small resting B cells but induces naturally occurring large B cells (which have presumably been preactivated in vivo) to synthesize DNA and to secrete IgM and low levels of IgG. B cells activated by anti-Ig antibodies apparently only become responsive to the factor once they have reached late G1 stage. All bioactivities of interleukin 4 are associated with a protein of Mr 44,000 (by NaDodSO4/PAGE). Therefore these results demonstrate that this lymphokine alone is sufficient to induce clonal expansion and maturation of activated B cells.     

Factors that affect human hemopoiesis are produced by T-cell growth factor dependent and independent cultured T-cell leukemia-lymphoma cells

Some laboratory results and clinical situations suggest that human T cells may be important in the regulation of growth of hematopoietic cells. Since the discovery of T-cell growth factor (TCGF), systems are now available for the long-term specific in vitro propagation of mature normal or neoplastic human T cells, providing an opportunity to study the influence of T cells on hematopoiesis. Recently, 24 cell lines from patients with cutaneous T-cell lymphoma (CTCL) and T-cell acute lymphoblastic leukemia (T-ALL) were grown with TCGF and then assessed for release of humoral factors that affect hematopoiesis. Conditioned media (CM) from these cell lines were tested for erythroid burst- promoting activity (BPA) and granulocyte colony-stimulating activity (CSA). BPA was detected in CM from 3/6 cultures of T-ALL patients and 4/6 CTCL cultures. CSA was found in the CM from 6/8 cultures of T-ALL patients, 7/12 CTCL cultures, and 3/4 CTCL cell lines that become independent of exogenous TCGF for growth. The CSA from several of the neoplastic T-cell cultures stimulated high levels of eosinophil colonies, a possible source of the eosinophilia seen in these patients. The ability of continuously proliferating human T lymphocytes, which retain functional specificity and responsiveness to normal humoral regulation, to produce factors that directly or indirectly stimulate myeloid and erythroid colony formation lends further credence to the role of T lymphocytes in regulating hematopoiesis.     

Production of B-cell growth factor interleukin 2 and gamma interferon by peripheral blood lymphocytes from patients with chronic lymphocytic leukemia of B-cell type

Chronic lymphocytic leukemia of B-cell type (B-CLL) is a malignant disease characterized by monoclonal proliferation of small lymphocytes of B-cell origin, usually associated with suppression of polyclonal B-cell activation (i.e., proliferation and differentiation). Normal human B-cell proliferation is controlled by different T-cell-derived lymphokines, including interleukin 2 (IL2) and gamma interferon (gamma-IFN), that account for the majority of the B-cell growth factor (BCGF) activity produced by mitogen-activated peripheral blood mononuclear cells (PBMCs). We have previously shown an increased and dysregulated secretion of IL2 in peripheral blood from patients with B-CLL. BCGF, IL2, and gamma-IFN productions by phytohemagglutinin (PHA)-stimulated PBMCs were investigated in 13 patients with active untreated B-CLL and 11 healthy donors. B-CLL PBMCs produced a significant amount of BCGF (6 U/ml) despite the low percentage of T cells (10%) associated with this disease as compared with that found in healthy donors (61%). BCGF production in normal controls and B-CLL patients was tripled after irradiation of PBMCs or addition of indomethacin. gamma-IFN secretion in B-CLL patients was decreased when compared with normal controls. Therefore, when gamma-IFN was calculated per fixed number of T cells, production was significantly higher in B-CLL patients than in normal controls, showing a dilution of the productive cells. This study suggests that T cells from B-CLL patients are functional in terms of BCGF production despite their decreased percentage and abnormalities in surface markers.     

Isolation and characterization of growth factor(s) from a human B-cell lymphoma

We demonstrate that human neoplastic B cells (Br cells) contain a cytoplasmic protein of molecular mass 60 Kd that exhibits B-cell growth factor (BCGF) activity on growth factor-dependent long-term human B cells as well as on autochthonous tumor cells. This 60-Kd protein is recognized by antibodies against a similar intracellular 60-Kd protein derived from normal human lymphocytes. These results demonstrate that the two proteins share epitope homology. Microculture bioassays indicate that neoplastic and normal 60-Kd proteins are capable of driving neoplastic B cells through S-phase. Western immunoblot analysis indicates that neoplastic B cells secrete 60- as well as 14-Kd protein. Immunoaffinity-purified proteins secreted by Br cells exhibit BCGF activity in anti-IgM or dextran sulfate-preactivated human B cells. In addition, a double-antibody immunofluorescence staining technique was used to demonstrate that Br cells express cell surface receptors for BCGF molecule(s). These studies provide support for the autocrine growth model for neoplastic human B cells and suggest that the autocrine growth factor derived from such tumor cells is similar if not identical to normal BCGF molecules.     

Characterization of a murine lymphokine distinct from interleukin 2 and interleukin 3 (IL-3) possessing a T-cell growth factor activity and a mast-cell growth factor activity that synergizes with IL-3.

Murine mast-cell and T-cell growth factor activities, distinct from interleukins 3 and 2 (IL-3 and IL-2), have been identified and partially purified from the supernatant of the activated helper T-cell line Cl.Ly1+2-/9. This mast-cell growth factor (MCGF) activity supports only low levels of proliferation of several IL-3-dependent mast-cell lines and synergistically enhances the growth of mast cells in the presence of IL-3. The T-cell growth factor (TCGF) stimulates the proliferation of several T-cell lines, but to a lesser extent than recombinant IL-2. The MCGF and TCGF activities were not separable despite multiple biochemical fractionations, suggesting that both activities reside in the same protein. The MCGF/TCGF was separated from endogenous IL-3 by cation-exchange chromatography at neutral pH and could be distinguished from IL-2 by unique elution conditions from reverse-phase columns. Two bands of MCGF/TCGF activity were eluted from gels after sodium dodecyl sulfate/PAGE; under nonreducing conditions, the activities corresponded to molecular masses of 20 and 15 kDa, while after reduction, the molecular masses were 21 and 16 kDa. Thus, both activities may correspond to single polypeptide chains. The majority of the MCGF/TCGF activity appears to reside in the 20-kDa species, which displays a pI of 6.2 on chromatofocusing.     

Interleukin 5, a T-cell-derived B-cell differentiation factor also induces cytotoxic T lymphocytes.

We describe an interleukin, termed interleukin 5, that is the recombinant product previously referred to as T-cell-replacing factor (TRF), B-cell growth factor II (BCGF II), or killer-helper factor (KHF). TRF has been defined as a T-cell-derived lymphokine that acts on activated B cells as a B-cell differentiation factor. We have previously demonstrated that TRF is identical to BCGF II and induces expression of receptors for interleukin 2 (IL-2) on activated B cells. We also have reported that KHF can induce not only expression of IL-2 receptors on peanut agglutinin-binding (PNA+) thymocytes but also generation of cytotoxic T lymphocytes (CTL) in PNA+ thymocytes in the presence of IL-2. We show here that culture supernatants of T-cell hybridomas that produce TRF as well as TRF purified by high-pressure liquid chromatography (HPLC-TRF) have KHF activity and generate CTL in PNA+ thymocytes in the presence of stimulator cells and IL-2. Moreover, translation products (recombinant TRF) of Xenopus oocytes injected with cDNA encoding for murine TRF (BCGF II) also exert KHF activity. A rat monoclonal anti-TRF antibody TB13 can block generation of CTL by HPLC-TRF or recombinant TRF. These results indicate that TRF acts not only on B cells as BCGF II but also on PNA+ thymocytes as KHF. In view of the diverse activities and targets of TRF, we propose that TRF refers to a different interleukin, interleukin 5.     

B-cell growth factor (B-cell growth factor I or B-cell-stimulating factor, provisional 1) is a differentiation factor for resting B cells and may not induce cell growth.

B-cell growth factor I [BCGF I or B-cell-stimulating factor, provisional 1 (BSFp1)] has been defined as a T-cell-derived lymphokine that acts as a co-stimulator of polyclonal B-cell growth in B cells cultured with anti-mu, anti-delta, or anti-Ig. Based on a number of studies it has been suggested that anti-Ig induces cell enlargement, entry into the G1 phase of the cell cycle, and expression of receptors for BSFp1. BSFp1 then induces entry of the cells into S phase. By adding BSFp1 prior to anti-Ig, we have found evidence that BSFp1 renders cells susceptible to anti-Ig-mediated entry of cells into G2/S phase. In contrast, if cells are first treated with anti-Ig, washed, and then cultured with BSFp1, they do not enter S phase. Taken together, these results suggest that BSFp1 acts on the resting B cells not as a growth factor but rather as a lymphokine that prepares cells for anti-Ig-mediated activation. Taken together with previous reports that BSFp1 induces increased expression of Ia antigens on resting B cells, these studies suggest that BSFp1 may be a differentiation factor rather than a growth factor and that it acts on resting B cells.     

Human T-lymphocyte growth factor: regulation of growth and function of T lymphocytes

The discovery of T-cell growth factor (TCGF) has made it possible to now routinely grow in tissue culture normal and neoplastic human T cells for long periods and in large amounts. TCGF has been recently purified. It is a small protein released by a subset of mature T cells following lectin-antigen activation, which in turn acts upon other T- cell subsets that have developed specific receptors for TCGF after lectin-antigen stimulation. Thus, release of TCGF and development of receptors for it appear to be obligatory for the clonal expansion of all activated T cells. Unlike normal T cells, neoplastic T cells respond directly to TCGF, requiring no prior in vitro lectin-antigen activation. This has led to the development of several new cell lines from patients with T-cell leukemias and lymphomas. In some cases, these cells become independent of exogenous TCGF by producing their own growth factor, implying a role for TCGF in the continuous proliferation of these cells. These developments necessitate a reevaluation of some concepts of immunoregulation of T-cell activities in terms of production and response to TCGF. In addition, this information has clinical implications. Recent results have shown that a major defect of the athymic nude mouse is the inability to produce TCGF and that some immunosuppressive agents, such as glucocorticosteroids and cyclosporin- A, exert their effects on T cells by disrupting the TCGF-T-cell interaction. Some human immune deficiencies might be due to a failure to respond to or to produce TCGF, which in some cases might be corrected by exogenous TCGF.     

Coordinated action of IgE and a B-cell-stimulatory factor on the CD23 receptor molecule up-regulates B-lymphocyte growth.

The CD23 (BLAST-2) antigen, recently identified as the low-affinity IgE receptor of B lymphocytes, has also been implicated as the focus for growth-promoting signals delivered to activated B cells by a low molecular weight B-cell growth factor (BCGF). Here we show that IgE and BCGF can coordinate B-lymphocyte growth through their opposing effects on the CD23 molecule. While the activation of purified quiescent B cells with phorbol 12-myristate 13-acetate led to the induction of 45-kDa CD23 at the surface membrane, the inclusion of IgE increased CD23 expression by a factor of approximately equal to 5. The addition of BCGF resulted in the rapid release of a 35-kDa form of CD23 from the cell surface. This shed molecule is associated with autocrine growth factor activity. Substantially more of this material was generated by BCGF acting on cells that had been stimulated in the presence of IgE. The combined effects of IgE and BCGF on DNA synthesis in activated B cells were more than additive. IgE similarly augmented the stimulatory capacity of a CD23 antibody that mimics the biological actions of BCGF. Binding of the anti-receptor antibody to its 45-kDa target at the B-cell surface also prompted the release of the 35-kDa soluble species. These results demonstrate a pleiotropy in the CD23 molecule with regard to both ligand binding and the subsequent behavior of the receptor. The ability of this single receptor to orchestrate a B-lymphocyte response through a variety of ligands and its role in normal and transformed autocrine growth are discussed.     

Evidence for an intracellular precursor for human B-cell growth factor.

Human B-cell growth factor has been described as a trypsin-sensitive protein of Mr 12,000-14,000. Evidence is provided herein that this relatively low molecular weight product may be released from a larger precursor molecule of Mr 60,000-80,000. The precursor protein is confined to the cytosol of freshly isolated T lymphocytes, and only the Mr 12,000-14,000 moiety is released upon lectin stimulation. The precursor protein was subjected to limited tryptic digestion, which demonstrated that the biologically active fraction of the moiety resided in a relatively low molecular weight fragment. The T lymphocyte routinely possessed an intracytoplasmic pool of the precursor protein, the amount of which cyclically varied depending upon its depletion by the secretion process of a lower molecular weight product. Analysis of the mRNA size coding for the majority of B-cell growth factor activity, determined by translation in Xenopus laevis oocytes, suggested that the B-cell growth factor-specific mRNA resided in the greater than or equal to 15S range. This value is consistent with the size of the larger precursor. Therefore, it is proposed that a precursor-product relationship exists for the processing of human B-cell growth factor, analogous to that which has been described for several other cytokines.     

Functional diversity within the suppressor phenotype as defined by monoclonal antibody in T-cell prolymphocytic leukemia

A patient with T-cell prolymphocytic leukemia (T-PLL) is described. The malignant T-cells from the patient were predominantly Leu-2-positive, indicating a suppressor phenotype. The cells were then tested to determine their functional capabilities. The patient's Leu-2-positive cells initially suppressed B-cell proliferation, as predicted by their phenotype but later functioned as T helper cells in the pokeweed mitogen system without a change in phenotype. The cells also responded inadequately to alloantigen and mitogen despite addition of exogenous T-cell growth factor (TCGF). Leu-2-positive prolymphocytes from the spleen of the patient were constitutive producers of TCGF. Surface phenotype using monoclonal antibody was inadequate to predict T-cell function of the cells from this patient with T-PLL. In addition, these data suggest there may be functional subpopulations within the OKT8+ phenotype. Constitutive TCGF production by malignant post-thymic T-cells may represent a mechanism by which these cells sustain their own growth.     

Increased expression of Ia antigens on resting B cells: an additional role for B-cell growth factor.

The present studies demonstrate that both T-cell-derived supernatants containing B-cell growth factor (BCGF or BSF) and a partially purified preparation of the B-cell growth factor (BSF-p1) induce an increase in the expression of IA and IE-encoded antigens on small resting B cells. This increase is detectable by 6-8 hr after initiation of culture and is relatively selective, since levels of surface immunoglobulin and H-2 antigens do not increase to the same extent. Although interferon-gamma induces increased expression of Ia antigens on macrophages and dividing neoplastic B cells, it does not induce an increase in the expression of Ia antigens on resting B cells. These results demonstrate that BSF-p1 may play two roles: (i) it acts on resting B cells to increase the levels of Ia antigen expression; and (ii) it sustains the growth of B cells that have been previously activated with mitogens, antigens, or anti-Ig.