Naturally occurring, spleen-associated suppressor activity of the newborn mouse. Biochemical and functional identification of three monokines secreted by newborn suppressor-inducer monocytes

Development of neonatal Th1/Th2 function

Newborn animals generally mount poor T cell-mediated immune responses in vivo. As a result, neonates fall prey to infectious agents and diseases which have little impact on immunocompetent adult animals. For some time, it was believed that this phenomenon was due to an intrinsic inability of newborns to mount developmentally mature Th1 responses. Recent studies in mice have challenged that view; under certain conditions, adult-level Th1 function has been achieved in newborns. More often, however, neonates develop Th2-dominant responses. A major challenge in the field of developmental immunology is to understand why the 'default' response for neonates is Th2 function. Cell intrinsic as well as environmental influences may contribute to Th2 skewing in neonates.

Exclusive Th2 primary effector function in spleens but mixed Th1/Th2 function in lymph nodes of murine neonates

Recent studies have shown that neonatal mice are competent to develop mature, Ag-specific Th1 function in situ. However, under many conditions, Th2 responses dominate in the neonate, while Th1 responses are more prevalent in adults. To compare further the immune responses of neonates and adults, we used the enzyme-linked immunospot method to measure the frequencies of primary Th1/Th2 effectors generated in situ in the spleens and lymph nodes. As assessed by the detection of IFN-gamma- or IL-4-producing cells, adults developed mixed Th1/Th2 responses in both organs. Neonatal lymph nodes contained mature frequencies of IFN-gamma- and IL-4-producing cells. In striking contrast, while mature frequencies of Th2 cells developed in neonatal spleens, virtually no IFN-gamma-secreting cells were detected. Exclusive Th2 function was observed in both BALB/c and C57BL/6 neonates, strains in which the Th2 and Th1 lineages, respectively, are favored in adults. Although Th1 effectors were virtually undetectable, the addition of rIL-12 boosted the frequency of IFN-gamma-secreting cells to adult levels. Therefore, Th1 effectors apparently developed in situ, but Th1 effector function either was not promoted or was inhibited upon subsequent exposure to the Ag in culture. Together, these results indicate that the quality of a primary Th response in neonates is strongly dependent on the site of initial Ag exposure; responses initiated in the lymph nodes are mixed Th1/Th2, whereas responses occurring in the spleen are heavily Th2 biased.

The identification of the neonatal NBXFO hybridoma cell and its mediator

The neonatal spleen:myeloma hybridoma cell, NBXFO, with immunosuppressive properties supported rodent hematopoietic colony formation. We identified this hybridoma to be an undifferentiated fibroblast that produced macrophage colony-stimulating factor (M-CSF). The bone marrow cells that grew in the presence of the NBXFO supernate were macrophages and were immunosuppressive towards lymphocytes. Neutralizing anti-M-CSF antibody partially inhibited the actions of the neonatal splenic suppressor cells. Neonatal splenocytes, but not the other parental cell line, FO, induced macrophage colony formation, possessed surface-associated M-CSF, and possessed M-CSF-specific transcripts. Therefore, we believe that the M-CSF-producing phenotype was contributed by a fibroblastic stromal cell and that these stromal cells could be responsible for the in situ generation of neonatal splenic suppressor cells.

Species-nonspecific action of soluble immunosuppressive factor produced by murine immature erythroid cells

Immature murine erythroid cells have natural suppressor cell activity suppressing in vitro mouse plaque-forming cell response and LPS-stimulated proliferative response of mouse spleen cells. A cell population enriched by erythroid precursors can produce a soluble activity with similar suppressive abilities. This erythroid suppressor activity (ErSF) has a low Mr (1 to 10 kDa). It can suppress both IgM and IgG secretion of PWM-stimulated human B cells and inhibit the proliferative response of PWM-stimulated human B lymphocytes, thereby indicating a species-nonspecific type of action. Antigen-induced mouse PFC response and mitogen-stimulated mouse and human B cell proliferation were inhibited dose dependently by the addition of ErSF, which did not significantly reduce cell viability, however. Kinetic studies showed that ErSF suppressed Ig secretion and proliferation of mitogen-stimulated B lymphocytes in all culture periods. The suppressive effect of ErSF on B cell proliferation was indirect, requiring the presence of IL-2 (but not of IL-1 alpha, IL-1 beta, or BCGF). In the presence of IL-2, the proliferative response of SAC-stimulated B cells was suppressed by ErSF when added at all time intervals studied but was maximal when ErSF was added on the third day of culture. The role of suppressor factor produced by immature murine erythroid cells in the phenomenon of "natural suppression" has been discussed.

Secretion of a suppressor cell inducing factor by an interleukin 3-dependent cell line with natural cytotoxic activity. III. Comparison with other interleukin 3-dependent cell lines

We previously described the interleukin 3 (IL-3)-dependent cell line, M1-A5, which has both natural cytotoxic (NC) and suppressor cell activities, the latter of which is mediated, in part, by the release of two cytokines which activate suppressor cells from unprimed lymphoid precursor cells. In this study we have compared the M1-A5 cell line with four other IL-3-dependent cell lines to determine whether these dual activities are universally associated with IL-3 dependence and to test the hypothesis that there is a direct relationship between the cytotoxic and the suppressive activities. The cell lines tested were a bone marrow derived Dexter culture derived line (FDC-P1), two Moloney leukemia virus induced leukemias (DA-1 and DA-3), and a mast cell line (PT18(A17]. All lines were dependent on IL-3 for survival but FDC-P1, DA-1, and DA-3 showed varying degrees of short-term proliferation in granulocyte-macrophage colony stimulating factor (GM-CSF). The cell lines all expressed asialo GM1 and Ly-5 surface markers but differed with respect to other markers. DA-1 expressed MAC-1, FDC-P1 and DA-3 expressed Thy-1, and PT18(A17) expressed receptors for the Fc portion of IgE. The cell lines varied greatly in their cytotoxic activity against WEHI-164. FDC-P1, DA-1, and PT18(A17) had low NC activity. DA-3 had consistently high activity, greater than that seen with M1-A5 cells. However, none of the cell lines secreted constitutively a suppressor cell inducing factor (SIF). In addition, it was demonstrated that recombinant murine TNF did not activate suppressor cells capable of inhibiting antibody synthesis and that anti-TNF did not block SIF activity, thus suggesting that TNF contamination of the M1-A5 derived SIF preparation is not responsible for the induction of suppressor cells. We conclude that suppressor cell inducing factors are not universally secreted by IL-3-dependent cell lines, that there is no correlation between NC and SIF activity, and that the dual activities of M1-A5 cells are not mediated by TNF.

NBxFO factor--a novel suppressor factor produced by fusion of neonatal spleen and a nonsecreting myeloma

Spleens from 1-day-old DBA/2J mice were fused to the nonsecreting myeloma, FO. Dialyzed supernates of these cells were found to suppress the antigen-specific proliferative response of cloned helper or alloreactive T cells at a final concentration of less than or equal to 5%. The same supernate-containing factor did not suppress the response to IL-2 of an IL-2-addicted T cell line. The factor was found not to suppress the production of either IL-2 or antibody, following stimulation of spleen cells with LPS. Absorption analysis revealed that the target of the factor was the accessory cell population. Further experiments indicated that the factor blocked the proliferation of thymocytes due to IL-1. Biochemical analysis revealed a molecular weight for the factor of about 90,000 and a pI of approximately 4.5.

Stimulation of suppressor cells in the bone marrow and spleens of high dose cyclophosphamide-treated C57Bl/6 mice

Systemic administration of a single dose (300 mg/kg) of cyclophosphamide (Cy) induced the appearance of a population of suppressor cells in the bone marrow and spleens of mice. Suppressor cells were assayed by their capacity to inhibit the concanavalin A (Con A) blastogenesis or the mixed-lymphocyte response of normal C57Bl/6 spleen cells. Cy-induced bone marrow (Cy-BM) suppressor cells were present as early as 4 days following Cy therapy and their activity gradually decreased over the next 2 weeks. Cy-induced splenic (Cy-Sp) suppressor cells were maximally present on Days 6 through 10 following Cy therapy. Studies were performed to characterize the suppressor cells of bone marrow obtained 4 days after Cy treatment and of normal bone marrow (N-BM). Some suppressor activity was present in normal bone marrow. N-BM suppressor cells resembled cells of the monocyte/macrophage lineage in that they were slightly adherent to Sephadex G-10, sensitive to L-leucine methyl ester (LME), and insensitive to treatment either with anti-T-cell antibody and complement or with anti-immunoglobulin antibody and complement. Their suppressive activity was abrogated by incubation with either indomethacin or catalase. Cy-BM suppressor cells were also resistant to treatment with anti-T-cell and anti-immunoglobulin antibody and complement but were not adherent to Sephadex G-10 and not sensitive to LME. Their suppressive activity was partially eliminated by indomethacin alone or in combination with catalase. We conclude that Cy chemotherapy induces the appearance of a population of immune suppressive cells and that these cells appear first in the bone marrow and subsequently in the spleen.