Isolation and identification of the naturally occurring, newborn spleen-associated suppressor cells. A mixed monocyte/mast cell population with separable suppressor activities

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.

GM-CSF augments the immunosuppressive capacity of neonatal spleen cells in vitro

Addition of exogenous granulocyte-macrophage colony stimulating factor (GM-CSF) to cultures of adult murine spleen cells with sheep red blood cells (SRBC) results in an augmented plaque forming cell (PFC) response. The influence of GM-CSF on the ability of neonatal spleen cells to suppress the anti-SRBC plaque forming response of adult spleen cells was tested by adding GM-CSF to cultures of neonatal and adult spleen cells. The suppressive capacity of the neonatal spleen cells was augmented by exogenous GM-CSF. The augmented suppression of the neonatal spleen cells was dependent on a G-10 adherent population since the addition of GM-CSF to cultures containing G-10 passed neonatal spleen cells resulted in an augmented PFC response and not suppression. Neonatal splenic glass adherent cells were also capable of suppressing the response. Neonatal spleen cells or purified neonatal glass adherent spleen cells cultured in the presence of GM-CSF had markedly increased levels of PGE2 in the culture supernatant. Neonatal spleen cells cultured with GM-CSF had increased numbers of morphologically identifiable macrophages after 48 hr of culture. Both irradiation and G-10 passage of the neonatal spleen diminished the numbers of macrophages formed in response to GM-CSF, and both of these manipulations resulted in reversal of suppression in response to GM-CSF. Thus, the augmented suppressive capacity of neonatal spleen cells in response to GM-CSF is probably mediated by its ability to drive monocyte to macrophage differentiation as well as increase the suppressive capacity of the existing neonatal splenic macrophages by increasing their production of PGE2.

Induction of non-specific suppressor cells and myeloregulatory effects of an immunomodulatory azaspirane, SK&F 105685

Administration of the immunosuppressive agent, SK&F 105685, has demonstrated immunosuppressive activity in several animal models of autoimmunity such as adjuvant arthritis and experimental autoimmune encephalomyelitis. The mechanism of action of SK&F 105685 in these autoimmune disease models appears to be the induction of non-specific suppressor cells (SC) detected in the spleen and bone marrow of treated animals. In this study we have examined the kinetics of SC appearance in the spleen and bone marrow following treatment with 30 mg/kg/day, p.o., for 1-6 days. SC activity was apparent following a single dose and increased with successive treatments. Treatment with SK&F 105685 also resulted in significantly enhanced myelopoiesis as measured by a 128% increase in the frequency of bone marrow myeloid progenitors (CFU-GM). Mechanistic studies indicated that in vitro treatment of bone marrow stromal cell cultures with SK&F 105685 upregulated the production of colony stimulating activity (CSA) detectable in a rat CFU-GM assay. Further, in vitro studies revealed that the SC in the bone marrow or spleens of SK&F 105685-treated rats admixed with normal marrow cells inhibited CFU-GM formation at a six-fold less cell concentration than cells obtained from control rats. These in vitro results suggest that the SK&F 105685-induced myelopoiesis is regulated by the subsequent generation of SC.

Suppressor function of hepatic mononuclear inflammatory cells during murine chronic graft-vs-host disease. I. Macrophage-enriched cells mediate suppression in the liver

Murine chronic graft-vs-host disease (CGBHD) to minor histocompatibility antigens (B10.D2----BALB/c) is characterized by inflammatory destruction of intrahepatic bile ducts, scleroderma-like skin lesions, and lymphoid involution. Spleen cells isolated from this model proliferate poorly when stimulated with mitogens. Previous reports indicate defective lymphocyte proliferation in this model is the result of active suppression induced by the graft-vs-host reaction in the spleen and is mediated by Thy 1.2-, sIg-, plastic nonadherent, splenic natural suppressor (NS) cells. To determine whether the intense CGVHD in the liver is associated with induction of suppression, we compared the suppressor activity of hepatic and splenic mononuclear inflammatory cells isolated concurrently during murine CGVHD. Both hepatic and splenic MC suppressed the proliferation of mitogen-stimulated normal spleen cells in a non-MHC, non-Mls restricted manner. T cells contributed to the suppressor activity of both populations. However, the suppressor activity of hepatic MC was mediated largely by a macrophage-enriched population of MC while that of splenic MC was mediated largely by NS cells.

Induction of non-specific suppressor cells in normal Lewis rats by a novel azaspirane SK&F 105685

SK&F 105685 (N,N-Dimethyl-8,8-dipropyl-2-azaspiro[4,5]decane-2- propanamine dihydrochloride) is a novel azaspirane which has therapeutic activity in rat models of autoimmune disease. In this study, we have demonstrated that SK&F 105685 is a potent inducer of non-specific suppressor cells (SC). Oral administration of 15-30 mg/kg/day results in the generation of SC in the spleen, lymph nodes and bone marrow, but not the thymus of Lewis rats. Splenic SC suppress Con-A-induced proliferation in co-culture assays at effector-responder ratios of 1:1 to 1:64. SC are radiation resistant (2000 R), non-T, non-B cells, partially adherent to plastic surfaces and are enriched in a 1.07 g/ml fraction of a Percoll density gradient. Their activity is increased, rather than ablated, by indomethacin. No definitive changes in Ig+, OX-19+, OX-8+, W3/25+ or asialo GM1+ cells could be detected in the spleens of treated rats compared to control untreated animals. Elevated levels of both radiation-sensitive and radiation-resistant suppressor cells were found in the bone marrow of treated rats in addition to the radiosensitive SC normally present in this tissue.

Regulation of autoimmunity in normal and rheumatoid individuals by bone marrow-derived natural suppressor cells and their suppressor factor: BDSF

Natural suppressor activity is defined as the ability of unstimulated effector cells to suppress responses of lymphoid cells to antigenic and mitogenic stimuli in an MHC unrestricted manner. We have described natural suppressor cells in bone marrow exerting such a function through a suppressor factor termed BDSF. In this report we demonstrate the ability of BDSF to regulate the in vitro EBV- and PWM-induced production of both IgM and IgM rheumatoid factor antibodies of lymphoid cells obtained from normal individuals and those with rheumatoid arthritis. BDSF therefore may play a role in the normal BM microenvironment suppressing primary IgM antibody responses. Since autoantibody responses are similarly suppressed, functional alteration or lack of BDSF may be responsible for the emergence of autoantibody-producing cells in bone marrow during certain autoimmune states.

Inhibition of animal models of autoimmune disease and the induction of non-specific suppressor cells by SK&F 105685 and related azaspiranes

SK&F 105685 (N,N-dimethyl-8,8-dipropyl-2-azaspiro[4.5]decane-2-propanamine+ ++ dihydrochloride), administered orally to adjuvant arthritic (AA) rats inhibited immune-mediated hindpaw inflammation with an ED50 of 20 mg/kg/day. Both prophylactic and therapeutic administration were effective in this model. In addition, SK&F 105685 inhibited skin wheal responses to purified protein derivative (PPD) of tuberculin in AA rats and the development of hindleg paralysis associated with experimental allergic encephalomyelitis (EAE). Spleens of normal rats treated with SK&F 105685 were found to contain a population(s) of suppressor cells (SC) which inhibited the response of normal cells to Concanavalin A (Con A) in co-culture assays. The association between SC induction and anti-arthritic activity was determined by evaluating a series of chemically related azaspiranes in the AA rat model and for SC induction in normal rats. A statistically significant correlation was demonstrated (r = 0.79, P less than 0.001), indicating that SC induction may be responsible for the therapeutic activity of these compounds.

Presence of natural suppressor cells in the chicken embryo spleen and the effect of virus infection of the embryo on suppressor cell activity

Spleen cells but not the thymus or the bursa cells of chicken embryos suppressed the in vitro mitogenesis of spleen cells of adult syngeneic or allogeneic chickens. The natural suppressor cell activity of embryo spleen was present at embryonation day 16, reached peak levels at embryonation day 18 and disappeared at hatch. The embryo spleen cells did not by themselves respond to phytohemagglutinin stimulation in vitro. The suppressive effect of embryonic spleen cells on adult spleen cells was present when the embryonic cells were added at the time of or after initiation of the adult spleen mitogenic cultures. When the embryonic cells were added to the cultures of adult spleen cells after the blastogenic response of the adult cells had peaked, the embryonic cells inhibited the incorporation of the label into adult spleen cell blasts. The suppressive activity of the embryonic spleen cells was mediated by soluble suppressor product(s) secreted by these cells, and direct cell-to-cell contact between embryonic and adult spleen cells was not necessary for suppression to occur. Infection of embryos with turkey herpesvirus and Marek's disease virus reduced the suppressor cell activity of embryonic spleen, although substantial residual suppressor cell activity remained in virus-infected embryos. Several pathogenic or non-pathogenic isolates of infectious bursal disease virus did not appreciably alter the suppressor cell activity of embryonic spleen cells.

The effect of in utero exposure to hexachlorobenzene on the developing immune response of BALB/c mice

BALB/c mice were exposed to 0.0, 0.5 and 5.0 mg/kg maternal body weight hexachlorobenzene (HCB) throughout gestation by daily per os dosing of the females. At 45 days of age selected immune functions of the offspring were assessed. The delayed-type hypersensitivity (DTH) response to oxazolone was severely depressed in animals exposed to either 0.5 or 5.0 mg/kg HCB, however, only those animals exposed to 5.0 mg/kg HCB showed a significant decrease in their mixed lymphocyte response (MLR) levels. The ability of isolated spleen cells to undergo a blastogenic response to concanavalin A (ConA), phytohemagglutinin (PHA) and lipopolysaccharide (LPS) showed no significant changes due to HCB exposure. Similarly, no significant difference in the induction of direct hemolytic plaque-forming cells was seen. A significant increase in the relative distribution of splenic T cells and a significant decrease in splenic B cells was measured in the offspring of HCB-treated females. These results suggest that HCB is capable of affecting the development or maturation of the immune response in mice, perhaps at the T cell level.

Suppression of natural killer cell activity in young and old mice

Spleen cells from female mice of the recombinant inbred strain BPS lack natural killer (NK) cytolytic activity, and can suppress the cytolytic activity of normal NK effector cells. The suppressor cells are not typical B cells, T cells, macrophages, or NK cells; they lack the characteristics and surface markers of each of these cell types. In BPS mice, suppressor cell activity is a dominant and significant characteristic of spleen cells at every age tested (2 weeks to 18 months). In other strains of mice which are normally classified as high-responders in NK assays, such as the C57BL strain, these suppressor cells are less prominent but can be detected when separated (on the basis of their higher density) from other spleen cell populations. As mice of the high-responder strains age, however, the suppressor cells become a significant part of the spleen cell population.

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

Immature monocytes residing in the spleens of newborn mice less than 6-7 days of age are known to suppress T-dependent and T-independent immune responses in vitro and in vivo. Suppression is mediated in part through products secreted by the newborn monocytes. In the present study, we have identified 3 monokines secreted by newborn, but not adult, monocytes correlating with materials possessing significant suppressor activity in vitro. These monokines have molecular weights of 58, 10.8, and 10 kilodaltons, appear to be proteins, and are insensitive to heat inactivation. The 58 kd material is antigenically distinct from alpha-fetoprotein, while the lower molecular weight materials are too large to be prostaglandins. Although these monokines can be shown to have activity in vitro, they are not as efficient as newborn monocytes in preventing alloreactivity in vivo.

Cloned natural suppressor cell lines derived from the spleens of neonatal mice

The establishment and characterization of cloned natural suppressor (NS) cell lines derived from the spleen of neonatal BALB/c mice are described. Cloned NS cells suppress the mixed leukocyte reaction (MLR) between normal adult responder and stimulator spleen cells with a 50-fold greater efficiency than fresh neonatal cells. Suppressive activity of both cells did not depend on the haplotype of the responder or stimulator cells, and was radioresistant. Cloned NS cells did not inhibit the uptake of [3H]thymidine by HT-2 cells proliferating in response to interleukin 2 (IL-2), nor the in vitro secretion of IL-1 by macrophages in response to lipopolysaccharide. Several experiments indicated that absorption of IL-2 could not explain the suppression of the MLR by the NS cells in the range of cell numbers tested. The results suggest that NS cells may suppress the MLR by interfering with early stages of T cell activation. The cell surface of a cloned NS cell line was examined using immunofluorescence staining, and was strongly positive for the Thy-1.2, Ly-5, and asialo-GM1 antigens. However, Lyt-1, Lyt-2, surface Ig, IE, MAC-1, and Fc and C3 receptor markers were not detected. In addition, NS cells showed no cytolytic activity against the YAC-1 target cell line. On the basis of these findings, cloned NS cells do not appear to be mature T cells, B cells, macrophages, or NK cells. The development of cloned NS cells may be useful in determining the identity and mechanism of action of nonspecific suppressor cells in the neonatal spleen, and their role in neonatal tolerance and maternal-fetal relationships.

The effect of prenatal chlordane exposure on the delayed hypersensitivity response of BALB/c mice

Previous studies in our laboratory have indicated that in utero chlordane exposure caused a significant enhancement in the survival of the offspring to influenza virus infection. Further studies, reported here, show that the non-specific delayed type hypersensitivity (DTH) response to oxazolone at 100 days of age, but not at 30 days of age, was significantly depressed. In contrast, the Con A-induced blastogenic response of spleen cells from chlordane-treated offspring was not depressed and was, in fact, significantly enhanced. However, neither the response to PHA nor to LPS mitogens was significantly altered. In utero exposure to chlordane significantly depressed the mixed lymphocyte reactivity (MLR) of spleen cells from male offspring, whereas females showed no significant alteration of MLR. The significant depression of the DTH and MLR responses supports our previous reports of enhanced survival of influenza virus infection following in utero exposure to chlordane, since active DTH contributes to the pathology of influenza virus infection in mice. The normal or enhanced T-cell mitogen response suggested that the chlordane-induced depression of DTH and MLR was not due to overt toxicity to T-cells.

Naturally occurring spleen-associated suppressor activity of the newborn mouse. Requirement for two genetic restrictions in suppression of lethal graft-versus-host disease by newborn spleen cells

Spleens from newborn mice less than 6-7 days of age are known to contain naturally occurring suppressor cells, which can suppress the immune reactivity of third-party adult cells. In the present study newborn spleen cell populations are shown to possess the potential to inhibit lethal graft-versus-host (GVH) disease in sublethally gamma-irradiated hosts injected with allogeneic adult cells. However, this capacity to suppress GVH disease is controlled by at least two genetic restrictions: (1) the newborn spleen cells and the adult donor cells must be histocompatible at an H-2-linked region apparently telomeric of H-2DL, and (2) the newborn spleen cells must express a strongly stimulating non-H-2 (perhaps M1s) alloantigenic phenotype. Host animals that survive GVH remain chimeric for at least 3-4 weeks but return to the host phenotype by 8-10 weeks. Thus, it appears that in sublethally irradiated hosts the newborn cells suppress donor cell reactivity long enough for the host system to recover from the effects of irradiation.