Rabbit bone marrow suppressor cells block the production or release of a soluble bone marrow growth factor

Fc gamma-receptor (Fc gamma R)-bearing cells from normal rabbit bone marrow suppressed the constitutive proliferation rates of the remaining, Fc gamma R-, cells. In the absence of the suppressive influences of Fc gamma R+ cells, cells in the Fc gamma R- population spontaneously elaborated a soluble growth factor (GF) which induced the proliferation of unseparated bone marrow cells. To examine regulation by Fc gamma R+ bone marrow cells, graded numbers of the Fc gamma R+ cells were mixed with constant numbers of the FcR- cells. At 24 hr, supernates were collected and tested for GF activity. The Fc gamma R+ suppressor cells efficiently and in a dose-dependent fashion blocked GF production or release. The GF was nondialyzable and relatively heat stable. Supernates with GF activity also had colony-stimulating factor activity, but were negative in assays modified from murine interleukin 1 (IL-1) and IL-2 assays. Regulation of GF production or release represents a new function for bone marrow suppressor cells.     

Murine IgA binding factors produced by Fc alpha R(+) T cells: role of Fc gamma R(+) cells for the induction of Fc alpha R and formation of IgA-binding factor in Con A-activated cells

The relationship between the production of a T cell factor having affinity for IgA (IgA-binding factor(s); IgA BF) and the expression of Fc receptors specific for IgA (Fc alpha R) was studied by using murine spleen cells activated with concanavalin A (Con A blasts). Fc alpha R was detected by the cytophilic binding of anti-TNP murine IgA myeloma protein (MOPC 315 IgA) to Con A blasts as determined by an indirect rosette method with trinitrophenylated sheep red blood cells (TNP-SRBC). After 18 hr preculture with IgA, Fc alpha R was expressed on 15 to 20% of Con A blasts, which released IgA BF suppressing the in vitro IgA synthesis of the spleen cells stimulated with pokeweed mitogen (PWM). Without preculture with IgA, there was neither induction of Fc alpha R nor the production of IgA BF from Con A blasts. Fc alpha R was not induced on Con A blasts by IgA if Fc gamma R(+) cells were depleted from the blasts by rosetting with SRBC sensitized with rabbit IgG antibody (EA gamma). Even after preculture with IgA, the suppressive IgA BF was undetectable in the culture supernatant of Con A blasts depleted of the Fc gamma R(+) cell population. By using a double rosette method with EA gamma and trinitrophenylated quail red blood cells, Fc alpha R proved to be co-expressed on Fc gamma R(+) precursor T cells in the Con A blasts. The results suggested that both Fc gamma R and Fc alpha R could be co-expressed on Con A blasts, as is the case with T2D4 Fc gamma R(+), Fc alpha R(+) T hybridoma cells, which are known to produce IgG-binding factor(s) (IgG BF) and IgA BF. The relationship between Fc gamma R and Fc alpha R on a single cell was studied by using monoclonal anti-Fc gamma R antibody (2. 4G2 ). The reactivity of 2. 4G2 antibody with T cell Fc gamma R was proved by the inhibition of EA gamma rosette formation by Con A blasts or T2D4 cells. The addition of 2. 4G2 monoclonal antibody, however, did not affect the induction of Fc alpha R on Con A blasts by IgA. Furthermore, the binding of IgA to Fc alpha R already expressed on L5178Y T lymphoma cell line cells was not inhibited by the monoclonal antibody. The results confirmed that Fc alpha R are distinct from Fc gamma R co-expressed on the same Con A blasts, and that the expression of Fc alpha R on Fc gamma R(+) T cells and their production of suppressive IgA BF may be induced by the binding of IgA to Fc alpha R.     

Purified Fc epsilon R+ bone marrow and splenic non-B, non-T cells are highly enriched in the capacity to produce IL-4 in response to immobilized IgE, IgG2a, or ionomycin.

Non-B, non-T cells from spleen and bone marrow cells produce IL-4 in response to cross-linkage of high affinity receptors for Fc epsilon R or Fc gamma RII, and to treatment with calcium ionophores. Cells bearing high affinity Fc epsilon R constituted 1 to 2% of non-B, non-T cells of spleen and of total bone marrow cells from naive donors. In mice whose immune systems had been polyclonally activated by injection with anti-IgD antibodies or had been infected with Nippostrongylus brasiliensis larvae, the frequency of Fc epsilon R+ cells in splenic non-B, non-T cells was also 1 to 2% but in bone marrow from anti-IgD-injected mice donors the frequency was approximately 5%. Cell sorting experiments revealed that all of the capacity to produce IL-4 in response to immobilized IgE or IgG2a or to ionomycin was found in the Fc epsilon R+ fraction. Among the Fc epsilon R+ spleen cells from naive donors, the frequency of IL-4-producing cells was 1/20 to 1/40 whereas in mice that had been injected with anti-IgD or infected with N. brasiliensis, the frequency of IL-4 producing cells in the Fc epsilon R+ population was approximately 1/5.     

Cytokine regulation of bone marrow natural suppressor cell activity in the suppression of lymphocyte function.

Natural suppressor (NS) cells, which nonspecifically suppress immune responses, are present in the spleen following exposure to radiation, chronic graft-versus-host disease, or cancer and in normal bone marrow. A model system is described which allows the study of cytokines activating and inhibiting NS cells, cytokines mediating NS activity, and NS effects on cytokine synthesis. Recombinant interleukin-3 (rIL-3) and granulocyte-macrophage colony-stimulating factor (rGM-CSF) efficiently activated NS cells present in normal bone marrow and were effective at concentrations as low as 5 U/ml. At high concentrations, GM-CSF, but not IL-3, did not activate NS cells. Recombinant interferon-gamma (rIFN-gamma) blocked the activation of bone marrow NS cells by rIL-3, but did not down-regulate NS cells once activated. The NS cells secreted one or more soluble suppressor factors, which blocked IL-2 synthesis and also inhibited IL-2-dependent T cell proliferation in the presence of excess IL-2.     

Splenic NK1.1-negative, TCR alpha beta intermediate CD4+ T cells exist in naive NK1.1 allelic positive and negative mice, with the capacity to rapidly secrete large amounts of IL-4 and IFN-gamma upon primary TCR stimulation

Splenic NK1.1+CD4+ T cells that express intermediate levels of TCR alpha beta molecules (TCRint) and the DX5 Ag (believed to identify an equivalent population in NK1.1 allelic negative mice) possess the ability to rapidly produce high quantities of immunomodulatory cytokines, notably IL-4 and IFN-gamma, upon primary TCR activation in vivo. Indeed, only T cells expressing the NK1.1 Ag appear to be capable of this function. In this study, we demonstrate that splenic NK1.1-negative TCRintCD4+ T cells, identified on the basis of Fc gamma R expression, exist in naive NK1.1 allelic positive (C57BL/6) and negative (C3H/HeN) mice with the capacity to produce large amounts of IL-4 and IFN-gamma after only 8 h of primary CD3 stimulation in vitro. Furthermore, a comparison of the amounts of early cytokines produced by Fc gamma R+CD4+TCRint T cells with NK1. 1+CD4+ or DX5+CD4+TCRint T cells, simultaneously isolated from C57BL/6 or C3H/HeN mice, revealed strain and population differences. Thus, Fc gamma R defines another subpopulation of splenic CD4+TCRint cells that can rapidly produce large concentrations of immunomodulatory cytokines, suggesting that CD4+TCRint T cells themselves may represent a unique family of immunoregulatory CD4+ T cells whose members include Fc gamma R+CD4+ and NK1.1/DX5+CD4+ T cells.     

IL-3, IL-4, and IL-6 enhance IFN-gamma-dependent bone marrow natural suppressor activity

The ability of murine bone marrow (BM) natural suppressor (NS) cells to suppress a Con A proliferation assay was greatly enhanced by supernatant obtained from the T cell hybridoma D9C1.12.17. Of the lymphokines produced by this hybridoma, three were found to enhance suppression: interleukin-3 (IL-3), IL-4, and IL-6. These molecules enhanced suppression of both unirradiated and irradiated (2000 R) BM cells indicating that augmented suppression was not just due to proliferation of NS cells. The ability of all three of the lymphokines to enhance BM suppression could be blocked by anti-interferon-gamma (IFN-gamma) antibody. These results indicate that (1) NS cell activity is not radiosensitive and (2) that two signals may be required for maximal NS cell suppression, one being a lymphokine-mediated signal and the other IFN-gamma.     

Structure and expression of Fc gamma receptors on mouse suppressor T cell hybridomas

Antigen-specific and idiotype-specific mouse suppressor T cell hybridomas were analyzed for the presence and specificity of Fc gamma receptors (Fc gamma R) by EA rosetting and by flow microfluorometry with the use of monoclonal antibodies. We found that four hybridomas expressed Fc gamma R specific for IgG1 and IgG2b, one of which became Fc gamma R- during prolonged culture. Four other hybridomas and the fusion parent, BW5147, consistently lacked Fc gamma R. The 125I-labeled Fc gamma R were isolated from surface radioiodinated hybridoma cells solubilized with 1% Nonidet P-40, were purified by using single or repetitive chromatography on mouse IgG-Sepharose columns, and were analyzed by SDS-PAGE. An 125I-labeled 56,000 to 61,000 Mr macromolecule was isolated from each of the Fc gamma R+ hybridomas, but from none of the Fc gamma R- hybridomas nor from BW5147 cells. This macromolecule rebound to insolubilized mouse IgG1, IgG2b, and human Fc fragments, but not to insolubilized mouse IgG2a, IgG3, or IgA or human F(ab')2 fragments, consistent with the specificity observed for Fc gamma R on intact hybridoma cells. The mouse suppressor T cell Fc gamma R differs in size and specificity from mouse B cell Fc gamma R. A 70,000 Mr protein expressed on all hybridomas and on BW5147 cells was radiolabeled and, despite preclearing with ovalbumin-Sepharose, bound to the mouse IgG-Sepharose columns, presumably due to mouse antibodies to gp-70. This macromolecule was completely and specifically removed by using goat antiserum to gp-70.     

IL-6 is a differentiation factor for M1 and WEHI-3B myeloid leukemic cells

IL-6 has multiple biologic activities in different cell systems including both the ability to support cell proliferation and to induce differentiation. We reported previously the isolation and functional expression of a mouse IL-6 (mIL-6) cDNA clone derived from bone marrow stromal cells. In this paper, we show that mIL-6 is a potent inducer of terminal macrophage differentiation for a mouse myeloid leukemic cell line, M1. Addition of mIL-6 to cultures of M1 cells rapidly inhibits their proliferation and induces phagocytic activity and morphologic changes characteristic of mature macrophages. These phenotypic changes are accompanied at the molecular level by a decrease in proto-oncogene c-myc mRNA accumulation and increases in Fc gamma R, proto-oncogenes c-fos and c-fms (CSF-1R) mRNA expression. Furthermore, IL-6 enhances the expression of Fc gamma R and c-fms in differentiation-responsive D+, but not unresponsive D- sublines of mouse myelomonocytic leukemic WEHI-3B cells. Together with our previous observation that IL-6 stimulates colony formation by normal myeloid progenitors, these results strongly suggest an important regulatory role for IL-6 in myeloid cell growth and differentiation.     

Function of the IL-2R for thymic and peripheral CD4+CD25+ Foxp3+ T regulatory cells

IL-2 contributes to the production, function, and homeostasis of CD4+CD25+ T(reg) cells. However, it remains uncertain whether IL-2 is essential for the development of T(reg) cells in the thymus, their homeostasis in the periphery, or both. The present study was undertaken to investigate the contribution of IL-2 during thymic T(reg) cell development and its maintenance in peripheral immune tissue. Relying on genetic mouse models where IL-2R signaling was either completely blocked or selectively inhibited in peripheral CD4+CD25+ T(reg) cells, we show that the IL-2/IL-2R interaction is active in the thymus at the earliest stage of the development of T(reg) cells to promote their expansion and to up-regulate Foxp3 and CD25 to normal levels. Furthermore, CD4+CD25+Foxp3+ T(reg) cells with impaired IL-2-induced signaling persist in the periphery and control autoimmunity without constant thymic output. These peripheral T(reg) cells with poor responsiveness to IL-2 exhibited slower growth and extended survival in vivo, somewhat lower suppressive activity, and poor IL-2-dependent survival in vitro. Mixed thymic and bone marrow chimeric mice showed that wild-type-derived T(reg) cells were substantially more effective in populating peripheral immune tissue than T(reg) cells with impaired IL-2 signaling. Collectively, these data support the notion that normally IL-2 is a dominant mechanism controlling the number of thymic and peripheral T(reg) cells.     

Suppression of the late stages of mitogen-induced human B cell differentiation by FC gamma receptors (FC gamma R) released from polymorphonuclear neutrophils

During short incubation in serum-free medium, polymorphonuclear neutrophils (PMN) release soluble material that can be characterized as receptors for Fc IgG (Fc gamma R) on the following evidence: it agglutinates erythrocyte-IgG antibody (EAG) complexes, it prevents the binding of EAG to EAG-rosette-forming cells, and it binds to EAG-rosette-forming cells after modulation of their Fc gamma R, allowing the formation of 'passive' rosettes. These Fc gamma R were isolated by affinity chromatography on sepharose 4B-IgG. This material was shown to interfere with the differentiation of peripheral blood B cells into Ig-secreting cells in cultures stimulated by pokeweed (PWM) or Nocardia opaca (NOC) extracts. The number of Ig-secreting cells determined by a reverse hemolytic plaque assay using protein A-coated sheep erythrocytes was decreased by addition of Fc gamma R over a wide range of dilutions. The number of Ig-containing cells was diminished in PWM-stimulated cultures, but not in cultures stimulated with NOC. Fc gamma R did not affect cell viability, nor did they interfere with plaque-forming cell assay. Fc gamma R was not suppressive when added before the 3rd day or after the 6th day of culture. The suppressor factor was shown to remain associated with Fc gamma R after elution at acidic pH; it was removed by absorption on Sepharose 4B-IgG, but not on pepsin-digested F(ab')2 fragments. The suppressive factor as well as the capacity to restore EAG rosette formation by modulated lymphocytes were destroyed by heating (56 degrees C, 30 min) or by freezing and thawing. Properties of Fc gamma R released from PMN in this system are similar to those of Fc gamma R released from unstimulated human peripheral blood lymphocytes (PBL) and to those of mouse Ig-binding factor produced by alloactivated T cells or T cell lines.     

Quantitative analysis of Fc gamma receptors on murine spleen cell populations by using dual parameter flow cytometry

The expression of Fc gamma R on subsets of mouse spleen cells was examined by dual parameter flow microfluorometry. B cells were detected by labeling them with antibodies against sIgM, sIgD, sIgG, or I-A; essentially all B cells expressed Fc gamma R. The number of Fc gamma R per cell on the sIgD+, sIgM+, and I-A+ cells averaged 2 X 10(4) receptors, and no correlation between the levels of expression of Fc gamma R and the B cell markers was evident. The sIgG+ B cells, however, expressed more Fc gamma R (8 X 10(4) receptors/cell) than sIgM+ and sIgD+ B cells. Fc gamma R on splenic macrophages were examined by double labeling spleen cells for Fc gamma R and Mac-1. The Mac-1+ cells (2 to 16% of the spleen cells) were 100% Fc gamma R+ and expressed threefold to fivefold higher numbers of Fc gamma R per cell than the sIgM+ or sIgD+ B cells. The Fc gamma R on T cells were studied on cells double labeled for Fc gamma R and Thy-1, Lyt-1, or Lyt-2. An average of 20% of the T cells expressed Fc gamma R and at least two subsets of Fc gamma R+ T cells were evident: Lyt-2- cells, most of which expressed intermediate (2 X 10(4) Fc gamma R/cell) levels of Fc gamma R, and Lyt-2+ cells, which expressed mainly high (8 X 10(4) Fc gamma R/cell) amounts of Fc gamma R. The levels of expression of Fc gamma R and sIgM increased dramatically in response to infection and were elevated in mice with genetic defects. We conclude that the level of Fc gamma R expression is a characteristic property of subsets of spleen cells from normal and infected mice.     

Ovarian carcinoma cells inhibit T cell proliferation: suppression of IL-2 receptor beta and gamma expression and their JAK-STAT signaling pathway

Deficient T cell immune function and intracellular signaling in cancer patients may result from effects of tumors or their products on lymphocytes. Recently, it was demonstrated that several ovarian carcinoma cell lines could produce soluble factors that inhibited T cell proliferation. The aim of this study is to assess the effect of supernatants from 3 ovarian carcinoma cell lines (OVCAR3, CAOV3, SKOV3) on signal transduction elements that are linked to the IL-2R and its JAK-STAT pathway. A profound inhibition of proliferation, lower level of IFN-gamma and higher level of IL-10 gene expression were observed when CD8+ T cells were co-cultured with supernatants from 3 ovarian carcinoma cell lines. Cell cycle studies on inhibited CD8+ T cells showed most of them were growth arrested in G0/G1 phase. Western blot analysis showed that tumor supernatants suppressed expression of JAK3 and tyrosine phosphorylation of STAT5. JAK1 was not altered and the inhibition of STAT3 only appeared in OVCAR3 cells. Tumor supernatants also partially blocked induction of IL-2R beta and gamma chains expression. These findings suggest that ovarian carcinoma cells may suppress T cell proliferation through inhibition IL-2 dependent signaling pathways, which may be a mechanism of ovarian carcinoma induced immunosuppression.     

Mouse skin graft prolongation with donor strain bone marrow and anti-lymphocyte serum: surface markers of the active bone marrow cells

The survival of C3H/HeJ skin grafts on B6AF1 mice treated with anti-lymphocyte serum (ALS) can be significantly prolonged by the injection of the host with C3H/HeJ bone marrow. Although the prolongation is apparently due at least in part to the ultimate presence in the host of specific suppressor cells of donor origin, little is known about the nature of the cells in the marrow inoculum that are responsible for this effect. The present investigation was undertaken to characterize surface markers of the active bone marrow cells. Marker-positive populations were either depleted and enriched by panning techniques or depleted by killing with specific antibody and complement, and then were assayed for their ability to prolong graft survival. Cells that were adherent to anti-Ia-coated plates extended graft survival only slightly better than did treatment with ALS alone, whereas nonadherent (Ia-depleted) cells, as well as cells treated with anti Ia and complement, retained good prolonging activity. Similarly, panning on anti-immunoglobulin (Ig)-coated plates produced an active, Ig+-depleted population and an inactive adherent population, and killing of Thy-1+ cells with antibody and complement did not compromise the ability of the bone marrow inoculum to prolong graft survival. Complement receptor-positive (EAC+) and Fc gamma receptor-positive cells (EA+) were separated by panning on plates coated with sheep erythrocytes/antibody/complement and erythrocytes/7S antibody respectively. Adherent, EAC+-enriched cells were only slightly active, whereas the nonadherent, EAC-depleted population was fully active in graft prolongation. However, both Fc gamma R+ (EA+)-enriched and depleted populations were active, with the enriched fraction producing significantly better prolongation than the depleted population. Thus, the bone marrow cells that can prolong skin graft survival in ALS-treated mice appear to be Ia-, Thy-1+, largely complement receptor negative, and Ig-, but are largely positive for Fc gamma receptors.     

Interleukin-2 enhances the growth of human melanoma cells derived form primary but not from metastatic tumours

Previously, we demonstrated that in vitro treatment of B16F10 murine melanoma cells with interleukin-2 (IL-2) enhances proliferation and metastasis. To further investigate the role played by IL-2 in human melanomas, we studied the expression of IL-2/IL-2 receptor and the effect of IL-2 on the proliferation of melanoma cell lines derived from primary (A375 and RMS cell lines) and metastatic (Hs294T cell line) tumours. We found a constitutive expression of cytoplasmic IL-2 and alpha, beta and gamma-subunits of the IL-2R on the surface of the three melanoma cell lines. The presence of IL-2 in the culture increased the proliferation rate in A375 and RMS cell lines, but no effect was observed in Hs294T metastatic cells. Biologically active IL-2 could be found in the supernatant of the three melanoma cell lines, particularly in A375 and RMS cells, in which an inhibition of the proliferation rate was observed when IL-2 was blocked. Moreover, the combination of anti-IL-2R beta and anti-IL-2R gamma blocking antibodies induced a significant down-regulation of cell proliferation in the three melanoma cell lines, and the combination of anti-IL-2R alpha, anti-IL-2R beta and anti-IL-2R gamma blocking antibodies inhibited IL-2-mediated growth stimulation in A375 and Hs294T cell lines. In RMS cells, a more significant effect was observed when only IL-2R gamma was blocked. Finally, exogenous IL-2 modulated the IL-2 endogenously produced by melanoma cells. These data show that IL-2 may modulate the growth of melanoma cells through autocrine or/and paracrine mechanisms.     

Stimulated rat T cell-derived inhibitory factor for cellular DNA synthesis (STIF). III. Effect on cell proliferation and immune responses

Stimulated T cell-derived inhibitory factor for cellular DNA synthesis (STIF), a lymphokine produced from concanavalin A (Con A)-stimulated rat suppressor T cells, was examined for its inhibitory effect on various cultured cells and on in vitro immune reactions. STIF could inhibit the DNA synthesis of a variety of normal and neoplastic cells from rats, mice, and humans in a dose-dependent fashion. Kinetics studies revealed that STIF selectively inhibited cellular DNA synthesis after incubation for 12 hr, but after 36 hr, it also inhibited RNA and protein syntheses. The inhibited cellular DNA synthesis by 12-hr incubation with STIF was recovered after culturing the cells in STIF-free medium. The inhibitory effect of STIF on the DNA synthesis was not blocked by addition of a sugar (alpha-methyl-D-mannoside, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, L-fucose, or L-rhamnose) in culture, as determined by using rat bone marrow cells. STIF inhibited proliferative responses of rat lymphocytes to T cell mitogens, Con A and phytohemagglutinin, and a B cell mitogen, lipopolysaccharide, as well as IL 2-dependent growth of cloned T572 cells. It could also inhibit both blastogenesis and cytotoxic T cell generation in allogeneic mixed lymphocyte reaction. The release of IL 2 from Con A-stimulated T cells was also inhibited by the added STIF in culture, as demonstrated from the finding that IL 2 activity was not detected in the supernatants even after an anion-exchange column chromatography. These results indicate that STIF could inhibit cellular DNA synthesis in a species-unrestricted manner and thus inhibits the proliferation of various normal and neoplastic cells, and that it could also inhibit lectin- or IL 2-dependent T cell proliferation as well as IL 2 production from T cells in in vitro immune reactions.     

Role of lymphokine-activated killer cells as mediators of veto and natural suppression

Fresh bone marrow cells have veto activity but little if any NK activity. By contrast, lymphokine-activated bone marrow cells have potent natural suppressor as well as veto activity, and also have cytolytic activity characteristic of lymphokine-activated killer cells. Veto activity of fresh bone marrow cells is eliminated by 9 Gy irradiation and by depletion of cells expressing Qa-2, but is unaffected by removal of cells expressing Thy-1, Qa-5, Ly-5, or asialo GM1. By contrast, the veto and NS activities of lymphokine-activated bone marrow cells are both abrogated by C lysis depletion of cells expressing Qa-2, Qa-5, Thy-1, asialo GM1, NK1, and Ly-11, but are unaffected by depletion of cells expressing Ly-2. Bone marrow cells depleted of Qa2+ cells fail to generate veto or natural suppressor activity when cultured in Con A-conditioned medium, unlike bone marrow cells depleted of mature NK1.1+ NK cells. Cloned NK cell line F8 is able to mediate both natural suppression and veto. These findings indicate that bone marrow veto and natural suppression are not mediated by T or NK cells present de novo in the bone marrow, but are dependent on proliferating cells that phenotypically resemble pre-NK cells. The progeny of these cells have the phenotype and functional activity of lymphokine-activated killer cells, and are capable of directly mediating both veto and natural suppression.     

Effects of thymic myoid cell culture supernatant on cells from lymphatic tissues

Conditioned media (MCM) of cloned thymic myoid cells (IT45R92, R613Ad, and R615B2) were used to investigate their possible involvement in thymic biological events. Those myoid cells produced in a culture medium biological activities capable of stimulating the growth of thymocytes, spleen cells, and bone marrow cells of mice and rats. Surface markers detected on spleen cells proliferating in MCM were characteristic of monocyte-macrophage lineages (C3R, Fc gamma R, asialo GM1) and T-cell lineages (Thy 1) but not B cells (sIgG). Chromatographic studies also suggested that the biological activities of MCM could be separated into two different molecular entities, such as a colony-stimulating activity and an interleukin 1-like activity which supported the growth of monocyte-macrophage lineages and T-cell lineages, respectively. These results indicate that thymic myoid cells produce cytokines important for the regulation of intrathymic interleukin cascade by which clonally differentiated thymic lymphocytes may be expanded into a sizable pool.     

Human IL-7: a novel T cell growth factor

IL-7 is a hemopoietic growth factor that induces the proliferation of early B lineage cells. In the course of studies to determine its effect on human bone marrow cells, we noted a marked outgrowth of mature T cells. When T cells from the circulation were cultured with IL-7, a dose-dependent proliferative response was observed. The target cells included both the CD4+ and CD8+ subpopulations of T cells, but the memory T cells (CD45R-) were better responders than unprimed T cells (CD45R+). IL-7 induced the expression of receptors for IL-2 and transferrin and higher levels of the 4F2 activation Ag. Although T cell responses to suboptimal concentrations of IL-7 were enhanced by the addition of IL-2, the proliferative response to IL-7 was not inhibited by neutralizing antibody to the IL-2R (Tac), nor was IL-2 secretion detected in this response. This response pattern of mature T cells suggests an important role for IL-7 in normal T cell physiology in humans.     

SF20/IL-25, a novel bone marrow stroma-derived growth factor that binds to mouse thymic shared antigen-1 and supports lymphoid cell proliferation.

Using a forward genetic approach and phenotype-based complementation screening to search for factors that stimulate cell proliferation, we have isolated a novel secreted bone marrow stroma-derived growth factor, which we termed SF20/IL-25. This protein signals cells to proliferate via its receptor, which we have identified as mouse thymic shared Ag-1 (TSA-1). Enforced expression of TSA-1 in IL-3-dependent Ba/F3 cells that do not express endogenous TSA-1 rendered cells to proliferate in a dose-dependent manner when stimulated with SF20/IL-25. FDCP2, a factor-dependent hemopoietic cell line that expresses endogenous TSA-1, could also be stimulated to proliferate with SF20/IL-25. Binding of SF20 to TSA-1 was blocked by anti-TSA-1 Ab and SF20-induced proliferation of TSA-1-expressing cells was inhibited by anti-TSA-1. In vitro assay revealed that SF20/IL-25 has no detectable myelopoietic activity but supports proliferation of cells in the lymphoid lineage.     

Rapid response to Con A by CD4+CD45R- rat memory lymphocytes as compared to CD4+CD45R+ lymphocytes

Functionally distinct subpopulations within the CD4+ subset of T lymphocytes have been described in man, rat, and mouse. In the rat different functions have been assigned to CD45R+ and CD45R- T helper cells. The CD45R+ in contrast to the CD45R- T helper cells have been reported to produce IL-2 and to proliferate well in response both to Con A and in MLR. In the present investigation the kinetics of the response to Con A by the CD45R+ and CD45R- rat T helper subsets have been analyzed. We confirm a strong proliferative response to Con A by CD4+CD45R+ rat T lymphocytes and also that they are the best IL-2 producers. We further demonstrate that CD4+CD45R- cells also produce IL-2, although in order to appreciate this production quantitatively by assays of the culture supernatants it was necessary to block IL-2 absorption by IL-2 receptor (IL-2R) antibodies. This blockage was of importance also in comparisons of the two subsets, since they showed different kinetics of IL-2R appearance. It is demonstrated that the CD4+CD45R- cells respond more rapidly to Con A than the CD4+CD45R+ cells as reflected by phenotypic conversion, IL-2 production, and proliferation. The fast response of the CD4+CD45R- T subset shown in the present study of rat cells and analogous studies of human cells suggests that the memory compartment of T cells besides other characteristics also has the capacity for a more rapid response than naive lymphocytes.