Activation of macrophage cytostatic effector mechanisms during acute graft-versus-host disease: release of intracellular iron and nitric oxide-mediated cytostasis

During acute graft-versus-host disease (GVHD) the activation of macrophages (Mphi) is mediated by 2 signals, interferon (IFN)-gamma and bacteria-derived lipopolysaccharide (LPS). A cascade of inflammatory responses that includes the release of mediators of tissue injury follows Mphi activation. Among the tissues characteristically targeted during acute GVHD are epithelial tissues of the skin and gastrointestinal tract that normally undergo continuous proliferation and are therefore sensitive to cytostatic processes. We have investigated whether Mphi can mediate cytostatic mechanisms capable of interrupting cell proliferation during acute GVHD. GVHD was induced in nonirradiated C57BL/6XAF(1) (B6AF(1)) mice by the injection of 60 x 10(6) (acute GVHD) or 30 x 10(6) (nonlethal GVHD) C57BL/6 (B6) lymphoid cells. Mphi from animals undergoing acute GVHD could be triggered by normally insignificant quantities of LPS to mediate a cytostatic effect on target cells, resulting in the complete shutdown of cellular proliferation. The same amounts of LPS had no effect on Mphi from normal or syngeneically transplanted animals. Mphi mediated the release of significant quantities of intracellular iron from target cells undergoing cytostasis. Reversal of cytostasis occurred following inhibition of nitric oxide (NO) production by N(G)-monomethyl-L-arginine (NMMA). Production of NO by LPS-triggered Mphi reflected the severity of GVHD. NO release increased significantly during acute GVHD but was only transiently increased during nonlethal GVHD. The results provide evidence that, as a result of activation during acute GVHD, Mphi produce NO and induce the release of iron from target cells, resulting in a potent cytostatic effect that inhibits cellular proliferation. (Blood. 2000;96:1836-1843)

The T-cell protein tyrosine phosphatase

In recent years, the T-cell protein tyrosine phosphatase (TC-PTP) has become an important member of the protein-tyrosine phosphatase (PTP) family in two aspects. Firstly, TC-PTP has been reported to act on downstream signalling events initiated by the epidermal growth receptor, suggesting that it may act as an important modulator of receptor tyrosine kinases and mitogenic signalling. Secondly, the finding of immune deficiency and lethality observed in TC-PTP null mice emphasizes the importance of this small PTP in the hematopoietic system. In this review, we provide a summary of the recent literature published on the TC-PTP and its various orthologs. Although much remains to be uncovered, some recent findings on the function of this small PTP suggest that it plays a critical role in regulating mammalian cell signalling.

Role of interferon-gamma in the priming of decidual macrophages for nitric oxide production and early pregnancy loss

We have previously shown that both priming and triggering signals were needed for nitric oxide production by decidual macrophages and that nitric oxide was responsible for embryo wastage. In this study, we investigated the role of IFN-gamma as the primary signal for macrophage activation in early embryo loss. IFN-gamma-deficient (GKO) and heterozygous F1 control mice were injected with lipopolysaccharide (LPS) at day 7 of gestation. The results showed that the GKO mice were more resistant to LPS-induced embryo loss than the wild type. This suggested that IFN-gamma was needed for LPS-induced embryo resorption and that decidual macrophages from pregnant GKO mice were not primed and could not be activated when given LPS. Further, the results showed that IFN-gamma mRNA was simultaneously expressed in the same embryos that also expressed mRNA markers for macrophage activation (TNF-alpha and iNOS), indicating that macrophage activation could be a consequence of IFN-gamma production. Similarly, we investigated the role of IL-12 as a switch cytokine capable of eliciting TH1-associated cytokine production including IFN-gamma. The results showed that IL-12 mRNA expression was correlated with IFN-gamma expression and macrophage activation. In this in vivo study, we showed for the first time that spontaneously increased decidual IFN-gamma expression is detrimental to embryo survival.

Impaired bone marrow microenvironment and immune function in T cell protein tyrosine phosphatase-deficient mice

The T cell protein tyrosine phosphatase (TC-PTP) is one of the most abundant mammalian tyrosine phosphatases in hematopoietic cells; however, its role in hematopoietic cell function remains unknown. In this report, we investigated the physiological function(s) of TC-PTP by generating TC-PTP-deficient mutant mice. The three genotypes (+/+, +/-, -/-) showed mendelian segregation at birth (1:2:1) demonstrating that the absence of TC-PTP was not lethal in utero, but all homozygous mutant mice died by 3-5 wk of age, displaying runting, splenomegaly, and lymphadenopathy. Homozygous mice exhibited specific defects in bone marrow (BM), B cell lymphopoiesis, and erythropoiesis, as well as impaired T and B cell functions. However, myeloid and macrophage development in the BM and T cell development in the thymus were not significantly affected. BM transplantation experiments showed that hematopoietic failure in TC-PTP -/- animals was not due to a stem cell defect, but rather to a stromal cell deficiency. This study demonstrates that TC-PTP plays a significant role in both hematopoiesis and immune function.

Early embryo loss is associated with the prior expression of macrophage activation markers in the decidua

In early embryo loss, the activation of maternal immune effector mechanisms play a critical role in determining the success or failure of a pregnancy. We have previously shown that increased nitric oxide production by decidual macrophages is involved in early embryo loss occurring at day 12 of gestation. In this study, using reverse transcription-PCR and Southern blotting, the expression of inducible nitric oxide synthases (iNOS) and TNF-alpha mRNA was determined to quantify macrophage activation in individual murine embryos in a model of spontaneous early embryo loss. At day 8 of gestation, 32 and 29% of embryos with no apparent pathology showed an increase in iNOS and TNF-alpha mRNA expression, respectively. This corresponds to the natural resorption rate seen in the mouse model. In addition, the percentage of embryos with increased iNOS and TNF-alpha mRNA expression was further augmented when pregnant mice were induced to abort at a higher rate. These results showed, for the first time, a correlation between increased iNOS and TNF-alpha expression and embryo resorption. The results provide evidence for the presence of activated macrophages at implantation sites before overt embryo damage occurs.

Early embryo loss is associated with the prior expression of macrophage activation markers in the decidua

In early embryo loss, the activation of maternal immune effector mechanisms play a critical role in determining the success or failure of a pregnancy. We have previously shown that increased nitric oxide production by decidual macrophages is involved in early embryo loss occurring at day 12 of gestation. In this study, using reverse transcription-PCR and Southern blotting, the expression of inducible nitric oxide synthases (iNOS) and TNF-alpha mRNA was determined to quantify macrophage activation in individual murine embryos in a model of spontaneous early embryo loss. At day 8 of gestation, 32 and 29% of embryos with no apparent pathology showed an increase in iNOS and TNF-alpha mRNA expression, respectively. This corresponds to the natural resorption rate seen in the mouse model. In addition, the percentage of embryos with increased iNOS and TNF-alpha mRNA expression was further augmented when pregnant mice were induced to abort at a higher rate. These results showed, for the first time, a correlation between increased iNOS and TNF-alpha expression and embryo resorption. The results provide evidence for the presence of activated macrophages at implantation sites before overt embryo damage occurs.

Progressive accumulation of bacterial lipopolysaccharide in vivo during murine acute graft-versus-host disease

In a previous report the authors demonstrated that acute graft-versus-host disease (GVHD) was associated with pathologic amounts of tumour necrosis factor alpha (TNF-alpha) and the appearance of lipopolysaccharide (LPS) in the blood of GVH reactive mice just prior to death. In this study the authors have investigated the kinetics of LPS accumulation in different organs during the course of acute GVHD using a murine model. Unirradiated C57BL/6 x AF1 (B6AF(1)) mice were transplanted with C57BL/6 (B6) lymphoid cells and killed at predetermined times after transplantation for LPS analysis. Control animals were injected with either 60 x 10(6) B6AF1 lymphoid cells (syngeneic) or 60 x 10(6) irradiated (2000 rad) CBA lymphoid cells (allogeneic). Lipopolysaccharide began to appear in the liver and the spleen of GVH reactive mice from day 2 post-transplant and by day 10 all GVH reactive mice tested positive for hepatic and splenic LPS. Low levels of LPS were detected in some control mice from days 2 to 10 post-transplant but LPS was never detected after day 10 in control groups. Total hepatic and splenic LPS in acute GVH reactive mice peaked at a time coincident with the appearance of LPS in the serum and with the onset of mortality. These results demonstrate that tissue levels of LPS increase throughout the course of acute GVHD and are sufficient to trigger the release of pathologic amounts of TNF-alpha from primed macrophages resulting in the cachexia and mortality associated with acute GVHD in this model.

IL-12 p40 messenger RNA expression in target organs during acute graft-versus-host disease. Possible involvement of IFN-gamma

The onset of acute graft-vs-host disease (aGVHD) is accompanied by macrophage (M phi) priming and the presence of bacteria-derived LPS in the sera of transplanted animals. Priming of M phi occurs during aGVHD despite the suppression of T cell function. We have investigated whether IL-12 mediates the continued production of IFN-gamma during the state of T cell immunosuppression that accompanies aGVHD. Acute GVHD was induced in nonirradiated AxC57BL/6F1 mice by the injection of C57BL/6 lymphoid cells. Despite T cell immunosuppression, M phi became primed, as shown by their expression of inducible nitric oxide synthase mRNA and their production of nitric oxide in response to LPS. Continual exposure to IFN-gamma was required to maintain a primed state in M phi during aGVHD. IL-12 p40 peptide mRNA was increased in M phi purified from animals undergoing aGVHD 14 days after transplantation. Target organs of aGVHD, including thymus, salivary gland, and lung, showed increased IFN-gamma mRNA between days 7 and 14 after transplantation. The increase was accompanied by an induction of mRNA for the p40 peptide of IL-12 and inducible nitric oxide synthase within the target organs. These results provide evidence for localized production of IFN-gamma within aGVHD target organs and suggest that it is mediated by LPS-induced production of IL-12 by M phi. Our data elucidate the mechanism of activation of M phi during aGVHD that results in TNF-alpha and nitric oxide production and delineates the effector role of M phi in the pathology of aGVHD.

IL-12 p40 messenger RNA expression in target organs during acute graft-versus-host disease. Possible involvement of IFN-gamma

The onset of acute graft-vs-host disease (aGVHD) is accompanied by macrophage (M phi) priming and the presence of bacteria-derived LPS in the sera of transplanted animals. Priming of M phi occurs during aGVHD despite the suppression of T cell function. We have investigated whether IL-12 mediates the continued production of IFN-gamma during the state of T cell immunosuppression that accompanies aGVHD. Acute GVHD was induced in nonirradiated AxC57BL/6F1 mice by the injection of C57BL/6 lymphoid cells. Despite T cell immunosuppression, M phi became primed, as shown by their expression of inducible nitric oxide synthase mRNA and their production of nitric oxide in response to LPS. Continual exposure to IFN-gamma was required to maintain a primed state in M phi during aGVHD. IL-12 p40 peptide mRNA was increased in M phi purified from animals undergoing aGVHD 14 days after transplantation. Target organs of aGVHD, including thymus, salivary gland, and lung, showed increased IFN-gamma mRNA between days 7 and 14 after transplantation. The increase was accompanied by an induction of mRNA for the p40 peptide of IL-12 and inducible nitric oxide synthase within the target organs. These results provide evidence for localized production of IFN-gamma within aGVHD target organs and suggest that it is mediated by LPS-induced production of IL-12 by M phi. Our data elucidate the mechanism of activation of M phi during aGVHD that results in TNF-alpha and nitric oxide production and delineates the effector role of M phi in the pathology of aGVHD.

The role of endogenous glucocorticoids on host T cell populations in the peripheral lymphoid organs of mice with graft-versus-host disease

Previously, we demonstrated that immature CD4+8+ and mature CD4+ thymocyte populations were selectively eliminated during murine graft-versus-host disease (GVHD) as a consequence of elevated levels of endogenous glucocorticoids. In this report, we investigated whether the marked reduction of CD4+8+ and CD4+ thymocyte populations would affect host CD4+ and CD8+ T cell populations in the spleens and lymph nodes (LN) of mice undergoing GVHD. GVHD was induced in (C57BL/6 x A)F1 (B6AF1) mice by injecting A strain parental lymphoid cells. Using an antibody against H2Kb antigens, labeled host B6AF1 cells were distinguished from unlabeled donor A cells. Our results demonstrated a marked deficiency of host CD4+ and CD8+ T cells in the spleens and LN of GVHD mice on day 21 after GVHD induction. The severe reduction of host T cell populations in the peripheral lymphoid organs did not appear to result from the elimination of CD4+8+ and CD4+ thymocyte populations. However, adrenalectomy before GVHD induction reversed the severe loss of both host CD4+ and CD8+ T cell populations in the LN of GVHD mice on day 21, whereas cortisone treatment of adrenalectomized (ADX) GVHD mice resulted in reduction of host LN CD4+ and CD8+ T cell populations similar to that observed in non-ADX GVHD animals on day 21. In addition, adrenalectomy markedly improved the proliferative response of LN T cells to mitogens when compared with immunosuppressed T cells from the LN of non-ADX GVHD mice. In contrast, adrenalectomy did not reverse splenic T cell immunosuppression and the marked reduction of splenic host T cell populations during GVHD. These results suggest that high levels of endogenous glucocorticoids during GVHD play a central role in mediating severe deficiency of host T cell populations and inducing severe T cell immunosuppression in the LN, but not in the spleen, of GVHD mice.

Increased expression of proopiomelanocortin (POMC) mRNA in adrenal glands of mice undergoing graft-versus-host disease (GVHD): association with persistent elevated plasma corticosterone levels

GVHD in animal models induces severe thymic atrophy as a result of prolonged secretion of high concentrations of adrenal glucocorticoids. In this study we investigated the mechanism responsible for the persistent stimulation of the adrenal glands to secrete glucocorticoids in mice undergoing GVHD. GVHD was induced across the major and multiple minor histocompatibility antigen difference in unirradiated C57Bl/6 x AF1 hybrid mice by the intravenous injection of A strain parental lymphoid cells. Our results showed plasma corticosterone (CS) levels were elevated in association with high concentrations of corticotropin (ACTH) in both the GVHD and control syngeneic (SYN) groups on day 9. By days 16 and 24, plasma CS and ACTH in the SYN mice returned to basal levels. In contrast, plasma CS levels remained elevated in the GVHD animals on days 16 and 24 despite decreasing concentrations of plasma ACTH. Reverse transcription-polymerase chain reaction (RT-PCR) showed several-fold increase in POMC mRNA in the adrenal glands of GVHD mice compared with SYN animals. In addition, high mRNA levels for murine prohormone convertase 1, the enzyme that cleaves POMC into ACTH, were also detected in GVHD adrenals. Histological analysis of GVHD adrenals failed to show any sign of adrenalitis, and RT-PCR of GVHD adrenals also failed to detect mRNA for interferon-gamma (IFN-gamma), a cytokine expressed by activated T and natural killer (NK) cells. However, mRNA for IL-12, a cytokine produced by activated macrophages, was increased in GVHD adrenals, suggesting that resident adrenal macrophages were activated during GVHD. Our findings suggest that persistent elevated levels of plasma glucocorticoids during GVHD could be mediated by intra-adrenal ACTH produced by resident adrenal macrophages activated as a consequence of GVHD.

Induction of a glucocorticoid-sensitive F1-anti-parental mechanism that affects engraftment during graft-versus-host disease

Studies have shown that graft-vs-host disease (GVHD) in animal models induces persistent elevated levels of circulating adrenal glucocorticoids. In this report, we investigated the effects of endogenous glucocorticoids on the outcome of GVHD by adrenalectomizing (ADX) unirradiated (C57BL/6 x A)F1 (B6AF1) mice before GVHD induction. GVHD was induced by injection of 20 x 10(6) A strain parental lymphoid cells into B6AF1 mice. Our results demonstrated that non-ADX recipient mice experienced features characteristic of GVHD on day 13, which became progressively more severe by days 18 to 21. The GVHD features included severe immunosuppression, reversal in the host splenic CD4+/CD8+ ratio, histopathologic lesions in different tissues, and high parental cell chimerism in the spleens and lymph nodes. In contrast, ADX F1 recipient mice experienced GVHD features on day 13 similar to their non-ADX counterparts; however, ADX animals recovered rapidly from GVHD by days 18 to 21. Flow cytometry showed that, although a relatively high frequency of parental cells was detected in the spleens and lymph nodes of ADX mice on day 13, nearly all of the parental cells in the peripheral lymphoid organs disappeared on days 18 to 21, the time of recovery from GVHD. The marked reduction of parental cells and recovery from GVHD were prevented by treating ADX F1 mice with either exogenous glucocorticoid, anti-asialoGM1, or anti-CD8, but not anti-NK1.1 Ab. These results suggest that a dramatic recovery from GVHD was induced by a cell-mediated, steroid-sensitive F1-anti-parental mechanism. The F1-anti-parental phenomenon described herein is different from classical hybrid resistance.

Induction of a glucocorticoid-sensitive F1-anti-parental mechanism that affects engraftment during graft-versus-host disease

Studies have shown that graft-vs-host disease (GVHD) in animal models induces persistent elevated levels of circulating adrenal glucocorticoids. In this report, we investigated the effects of endogenous glucocorticoids on the outcome of GVHD by adrenalectomizing (ADX) unirradiated (C57BL/6 x A)F1 (B6AF1) mice before GVHD induction. GVHD was induced by injection of 20 x 10(6) A strain parental lymphoid cells into B6AF1 mice. Our results demonstrated that non-ADX recipient mice experienced features characteristic of GVHD on day 13, which became progressively more severe by days 18 to 21. The GVHD features included severe immunosuppression, reversal in the host splenic CD4+/CD8+ ratio, histopathologic lesions in different tissues, and high parental cell chimerism in the spleens and lymph nodes. In contrast, ADX F1 recipient mice experienced GVHD features on day 13 similar to their non-ADX counterparts; however, ADX animals recovered rapidly from GVHD by days 18 to 21. Flow cytometry showed that, although a relatively high frequency of parental cells was detected in the spleens and lymph nodes of ADX mice on day 13, nearly all of the parental cells in the peripheral lymphoid organs disappeared on days 18 to 21, the time of recovery from GVHD. The marked reduction of parental cells and recovery from GVHD were prevented by treating ADX F1 mice with either exogenous glucocorticoid, anti-asialoGM1, or anti-CD8, but not anti-NK1.1 Ab. These results suggest that a dramatic recovery from GVHD was induced by a cell-mediated, steroid-sensitive F1-anti-parental mechanism. The F1-anti-parental phenomenon described herein is different from classical hybrid resistance.

Levels of p56lck and p59fyn are reduced by a glucocorticoid-dependent mechanism in graft-versus-host reaction-induced T cell anergy

The graft-versus-host reaction (GVHR) results in profound, long-lasting immunosuppression characterized by T cell unresponsiveness to antigenic and mitogenic stimuli. In this report, the roles of the protein tyrosine kinases p56lck and p59fyn in GVHR-induced T cell anergy were investigated. GVHR was induced by the intravenous transfer of parental lymphoid cells into F1 hybrid recipient mice. The levels of lck and fyn declined dramatically in splenic and lymph node T cells of mice undergoing GVHR as the reaction progressed and T cell immunosuppression developed. Adrenalectomy of the GVH-reactive mice prevented both the GVHR-induced reduction of lck and fyn and the long-term T cell unresponsiveness to mitogens, suggesting a glucocorticoid-mediated mechanism. Indeed, treatment with exogenous glucocorticoids induced lck and fyn down-regulation in the lymph node T cells of normal mice, and in cultured T cell clones. We propose that the increase in endogenous glucocorticoids during GVHR triggers a reduction in T cell lck and fyn, leading to the severe immunosuppression of GVHR; this may represent a general mechanism of glucocorticoid-mediated immune regulation.

A donor-derived asialo-GM1+ cell induces depression of B-cell genesis during systemic graft-versus-host disease

The nature of the effector cell(s) responsible for the depression of B-cell genesis in the bone marrow of mice undergoing systemic graft-versus-host disease (GVHD) has been examined. Donor C57BL/6 (B6) mice were treated in vivo with either a single injection of anti-asialo GM1 antibody (anti-ASGM1) to eliminate naturally occurring (endogenous) ASGM1+ cells or B6xAF1 (B6AF1) lymphoid cells followed by anti-ASGM1 to eliminate both endogenous and "induced" ASGM1+ cells. Lymphoid cells from donor mice after the elimination of endogenous ASGM1+ cells produced severe GVHD and concomitant depression of B-cell genesis when injected into B6AF1 recipients. In contrast, cells from donors depleted of both the endogenous and inducible ASGM1+ populations did not cause GVHD or depletion of B lineage cells in B6AF1 recipients but did depress B-cell genesis in B6C3F1 mice. The "induced" ASGM1+ cells were Thy 1+, but their elimination did not significantly alter either overall T-cell function or specific cytotoxic T-cell (CTL) reactivity against the sensitizing (B6AF1) strain. The results suggest that the effector cell responsible for the depression of B-cell genesis during systemic GVHD can be induced to express ASGM1, is strain-specific and Thy 1+; but is not a conventional CTL.

Irradiation of the skin and systemic graft-versus-host disease synergize to produce cutaneous lesions

In this report, the relationship between irradiation and graft-versus-host disease (GVHD)-induced cutaneous injury was investigated. Unirradiated F1 hybrid mice were grafted with irradiated skin and then injected with parental strain lymphoid cells to induce GVHD. Although low grade dermal lymphoid infiltrates were observed in unirradiated skin grafts of some GVH-reactive mice, and irradiated grafts of normal animals showed occasional fibrosis, only the irradiated grafts of GVH-reactive mice developed lesions consisting of vacuolar degeneration of the epidermal-dermal junction and necrotic keratinocytes accompanied by pronounced epidermal infiltrates, characteristic of clinical cutaneous GVHD. The results suggest that cutaneous irradiation exerts a permissive effect on lesion formation in the skin of mice undergoing GVHD. Furthermore, systemic irradiation, known to exacerbate the severity of GVHD, is not required. Cutaneous lesions may be triggered by radiation injury of keratinocytes, up-regulation of adhesion molecules on irradiated endothelium, destruction of protective radiosensitive intraepithelial lymphocytes, and radiation-induced priming of intradermal macrophages.

Thymic selection and thymic major histocompatibility complex class II expression are abnormal in mice undergoing graft-versus-host reactions

The graft-vs.-host reaction (GVHR) results in damage to the epithelial and lymphoid compartments of the thymus and thus in abnormal maturation and function of thymocytes in mice undergoing GVHR. In this report, the effects of GVHR on thymic T cell receptor (TCR) expression and usage have been investigated. GVHR was induced in unirradiated F1 hybrid mice by the intravenous transfer of parental lymphoid cells. Expression of the CD3/TCR complex on thymocyte subsets defined by CD4 and CD8 was studied by three-color flow cytometry. The level of CD3/TCR was decreased on CD4+CD8-, but not CD4-CD8+, mature thymocytes. The lack of upregulation of CD3/TCR on CD4 single-positive thymocytes, but not on their CD8+ counterparts, suggested an abnormality of class II major histocompatibility complex (MHC) expression in the thymuses of mice undergoing GVHR. Immunofluorescence staining of thymic frozen sections revealed that MHC class II expression was dramatically decreased in GVH-reactive mice. GVHR-induced changes in positive and negative selection were evaluated by determining the incidence of specific V beta TCR segment usage in the thymus. In normal mice, thymocyte usage of any given V beta segment was highly consistent between individuals of the same strain and age; however, a marked divergence in the incidence of TCR V beta 6hi and V beta 8hi cells between GVH-reactive littermate mice was observed, suggesting that thymic positive selection had become disregulated in these animals. Furthermore, negative selection was defective; the incidence of phenotypically self-reactive V beta 6hi T cells was significantly greater in the thymuses of GVH-reactive mice bearing the endogenous superantigen Mls-1a than in untreated controls. Thus, mice undergoing GVHR showed defective TCR upregulation on CD4+CD8- thymocytes and changes in TCR usage reflecting aberrant thymic selection, in conjunction with decreased expression of MHC class II. Most abnormalities of TCR expression and usage on CD4+ thymocytes observed in GVH-reactive mice were analogous to those of class II knockout mice.

Macrophage priming and lipopolysaccharide-triggered release of tumor necrosis factor alpha during graft-versus-host disease

In this report we have investigated macrophage (M phi) activity and tumor necrosis factor alpha (TNF-alpha) production during graft-vs.-host disease (GVHD). TNF-alpha production by M phi requires two signals: priming of M phi by interferon followed by triggering of TNF-alpha production and release by lipopolysaccharide (LPS). The state of M phi activation was examined in nonirradiated B6AF1 recipient mice injected with either 60 x 10(6) (acute GVHD) or 30 x 10(6) (nonlethal GVHD) parental B6 lymphoid cells. During the early phase of acute GVHD, administration of normally sublethal amounts of LPS-triggered release of significant amounts of TNF-alpha into the serum resulting in death of the animals within 36 h. Normal animals treated with the same dose of LPS neither died nor produced detectable amounts of serum TNF-alpha. In vitro studies demonstrated that M phi were primed during GVHD. The level of M phi priming was greater during acute GVHD than nonlethal GVHD since 100-fold less LPS was required to trigger killing of a TNF-alpha-sensitive cell line by M phi from acute GVHD animals. The amount of TNF-alpha released into the serum after LPS injection increased during the course of the GVHD and was significantly greater in acute GVH-reactive mice. Endogenous LPS was detected in the serum of acute GVH-reactive animals coincident with the onset of mortality. The data provide evidence that during GVHD M phi are primed as a result of the allogeneic reaction and that endogenous LPS therefore triggers M phi production of TNF-alpha resulting in the symptoms characteristic of acute GVHD.

Induction, specificity and elimination of asialo-GM1+ graft-versus-host effector cells of donor origin

In previous studies we demonstrated that an induced asialo-GM1 positive (ASGM1+) cell of donor origin that exerts natural killer cell-like activity (NK activity+) plays a crucial role in the development of graft-versus-host (GVH)-associated tissue damage and severe immunosuppression. This study examined whether the ASGM1+ (NK activity+) GVH effector cells were activated by non-specific signals or whether these cells were triggered by specific alloantigens and displayed antigenic specificity. C57B1/6 (B6) donor mice were treated with either B6 x AF1 (B6AF1) lymphoid cells and anti-asialo GM1 antibodies (anti-ASGM1) to induce and eliminate specifically activated B6-anti-B6AF1 ASGM1+ (NK activity+) cells or with polyinosinic: polycytidylic acid (poly I:C), and anti-ASGM1 to eliminate non-specifically activated ASGM1+ (NK activity+) cells. Donor spleen and lymph node cells depleted of the specific allo-induced ASGM1+ NK reactive cells showed near normal numbers of L3T4+ and Lyt-2+ cells and retained T- and B-cell functions as measured by mitogen responses (to PHA, Con A and LPS), mixed lymphocyte responses (MLR) (to B6AF1) and the generation of cytotoxic T cells (CTL) (to B6AF1 blasts). Anti-ASGM1 treatment almost completely abrogated NK activity in all donor inocula. GVH reactions were induced by injecting treated donor cells into B6AF1, B6 x C3HejF1 (B6C3HF1) and B6 x SJLF1 (B6SJLF1) hybrids and monitored by splenomegaly, suppression of T-cell mitogen responses and the development of histopathological lesions in the thymus, liver and pancreas. Cells from donors depleted of non-specifically (poly I:C) induced ASGM1+ cells induced severe histological lesions, marked immunosuppression and splenomegaly in all three F1 hybrid combinations. When the donor cells were depleted of specifically induced (B6-anti-B6AF1) ASGM1+ cells and injected into the three F1 combinations they induced splenomegaly in all three but caused severe tissue injury and intense immunosuppression only in B6C3HF1 and B6SJLF1 mice and not in B6AF1 mice. Genetic analysis suggests that the H-2D (or a closely related) region of the H-2 complex plays an important role in the activation of the specific GVH effector cells. These results suggest that the cell(s) responsible for splenomegaly are different from the ones that cause severe GVH-associated tissue damage and immunosuppression although there may be cells and/or lymphokines common to both processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of tumor necrosis factor alpha in the developing nervous system

We present evidence that tumor necrosis factor alpha (TNF-alpha) is transiently expressed at specific times during embryogenesis in precisely defined areas of the nervous system in two different classes of vertebrates. In murine embryos, TNF-alpha was detected in the brain, neural tube and peripheral mixed spinal nerves. In the chick embryo, TNF-alpha was observed in the brain neuroepithelium and in the developing Purkinje neurons of the cerebellum. Western immunoblot analysis revealed that brain tissue from both mouse and chick embryos contained a 50 kDa protein showing immunoreactivity with anti-TNF-alpha antibody. These results suggest that TNF-alpha participates in the normal development of the vertebrate brain and spinal cord.

The effect of the graft-versus-host reaction on B lymphocyte production in bone marrow of mice. Depressed genesis of early progenitors prior to mu heavy chain expression

The effects of systemic graft-versus-host (GVH) reactions on the early precursor cell populations involved in primary B lymphocyte genesis have been examined in the bone marrow of (C57BL/6xA)F1 mice injected with lymphoid cells from A strain mice. Double immunofluorescence labeling techniques for the intranuclear enzyme, terminal deoxynucleotidyl transferase (TdT), the B220 cell surface glycoprotein detected by monoclonal antibody, 14.8, and surface or cytoplasmic mu chains of IgM (s mu, c mu) were used to quantitate 3 putative early B lineage progenitors preceding mu chain expression (TdT+14.8-mu-, TdT+14.8+mu- and TdT-14.8+mu-), pre-B cells (c mu+, s mu-) and B lymphocytes (s mu+). After initiating GVH reactions, the early B precursor cells, pre-B cells, and B lymphocytes in the bone marrow all fell rapidly in numbers, being almost completely absent from 10-15 days to the end of the 30-day assay period. The decline of some of the early progenitors started at a later time and was less complete than that of the more differentiated B lineage cells. In the spleen, B lymphocytes declined rapidly in numbers after 8 days to less than 5% of normal values from 12 days onward. The results demonstrate that systemic GVH reactions in mice almost completely eliminate the B cell lineage, including early precursor cells apparently undergoing mu chain rearrangement in the bone marrow. The pattern of depletion suggests that a range of B lineage progenitor cells may be directly susceptible to GVH reactions. The findings contribute to a model for the pathogenesis of the humoral immunodeficiency of systemic GVH disease.

Lipopolysaccharide-induced fetal resorption in mice is associated with the intrauterine production of tumour necrosis factor-alpha

Certain strains of mice display an increased frequency of fetal resorption, but little is known about the effector mechanisms involved. We have examined the events associated with lipopolysaccharide (LPS)-induced fetal resorption in mice. Administration of 25 micrograms LPS on Day 12 of gestation resulted in the appearance of tumour necrosis factor-alpha (TNF-alpha) in the amniotic fluid and fetal resorption. Levels of LPS-induced TNF-alpha were reduced by 90% after pretreatment with the TNF-alpha-suppressing drug pentoxifylline (PXF). Treatment of pregnant mice during early gestation with 0.1 micrograms LPS resulted in fetoplacental resorption which was maximal when the LPS was given on Day 8. Resorption induced by 0.1 micrograms LPS on Day 8 of gestation was significantly reduced by pretreatment with PXF. Infiltration of asialo-GM1-positive cells was observed in the decidual-ectoplacental cone area of embryonic units from LPS-treated mice. In addition, treatment with anti-AGM1 antiserum prevented the LPS-induced resorption. Our results suggest that TNF-alpha and asialo-GM1-positive cells are involved in LPS-induced fetal resorption.

The effects of polyinosinic:polycytidylic acid on the graft-versus-host reaction. III: Increased severity of the reaction with delayed pI:C treatment

We have been investigating the effects of polyinosinic:polycytidylic acid (pI:C), an interferon inducer, on the graft-versus-host reaction. We have previously shown that pI:C treatment of C57BL/6xAF1 (B6AF1) recipient mice immediately before injection of C57BL/6 (B6) parental lymphocytes inhibited the immuno-suppression and pathological changes normally caused by the GVH reaction, by a mechanism apparently identical to that seen in F1 hybrid resistance (HR) to hematopoietic grafts. We now demonstrate that delaying pI:C treatment by as little as 48 hr produces the opposite effect. Treatment of recipient B6AF1 mice at different days after transfer of parental lymphocytes induced a marked increase in the severity of the GVH reaction, as measured by a decreased plaque-forming cell response to sheep erythrocytes; decreased proliferative response to the T and B cell mitogens PHA, Con A, and LPS; increased pathological changes in both lymphoid and nonlymphoid tissues; and increased GVH-associated mortality. This effect is unrelated to HR, as pI:C was able to augment the severity of the GVH reaction when A strain cells were injected into AxCBAF1 recipients, which do not manifest HR. Early pI:C treatment (1 and 2 days after parental cell transfer) increased the severity of the GVH reaction much more than later pI:C treatment (7 and 8 days after parental cell transfer). This observation, along with the demonstration of altered pathology in GVH mice treated with pI:C, suggests that the effect of pI:C is not mediated through a direct suppressive effect of IF on the cells responding in either the PFC or mitogen assays, but rather by the ability of IF to activate or suppress mechanisms involved in the development of GVH-induced alterations.

Genetics of resistance to infection with Candida albicans in mice

To determine differences in susceptibility, 234 naive mice including xid and beige mutants were infected intravenously with Candida albicans and monitored with survival analysis and quantitative culture of the kidneys. By using survival time as the criterion, animals of seven inbred strains were separated into three groups. C3H/HeJ and Dw/+ were most susceptible; C57BR/cdJ, BRVR and CBA/N (xid) were intermediate in susceptibility; C57BL/KsJ and C57BL/6J were least susceptible. Mean survival times (MST) were markedly influenced by the number of Candida cells injected while the ranking of mouse strains by survival alone was unchanged. There was a dissimilar behaviour of the strains to produce organ weight changes in response to infection when compared with uninfected mice which were matched for age and genetic lineage. Black mice had lower colony forming units (CFU) per mg of tissue at the time of death than animals of other genetic lineage. Nevertheless, the finding that MST and CFU studies were loosely correlated in a few strains of mice indicated that the proliferation of the fungus in the kidneys was not always the major cause of death. The beige mutation was found to determine an increased susceptibility to systemic Candida infection. The differences in survival for beige and nonbeige mice were influenced by the genetic lineage of the host, being much greater in the C57BL/6 strain (36.7 days) than in the C3H/He strain (5 days). C57BL/6 beige-J had significantly higher CFU per organ and per unit of weight than C57BL/6 +/+ mice. These data evinced an important contribution of host genetic factors to resistance to systemic candidiasis. It is suggested that innate resistance genes regulate the differentiation in the bone marrow and the function of cells of granulocyte-macrophage lineage.

Complete sequential regeneration of graft-vs.-host-induced severely dysplastic thymuses. Implications for the pathogenesis of chronic graft-vs.-host disease

This study presents the sequential morphologic regeneration of graft-vs.-host (GVH)-induced dysplastic thymuses in long-term survivors of GVH reactions. GVH reactions were induced in adult C57BL/6xAF1 (B6AF1) hybrids by injecting 20 x 10(6) A strain parental lymphoid cells (PLC). Starting on day 30 after GVH induction, five to ten animals were randomly selected from a pool of GVH-reactive mice and killed at various times. Each animal was tested for thymic histology and T cell functions. Thymuses taken on day 30 after GVH induction displayed severe dysplasia as characterized by lymphocytic depletion, complete effacement of cortico-medullary demarcation, and reduction and total loss of medullary epithelial cells or both. Starting by days 60-70 after GVH induction, at least four stages of thymic regeneration were identified. Day 60-70 thymuses displayed cortical regeneration and the reappearance of cortico-medullary demarcation. The medulla of these thymuses, although containing dark individual epithelial cells and numerous lymphocytes, was devoid of pale epithelial cells (stage 1). The medulla of thymuses on day 100 after GVH induction displayed a few sparcely distributed pale epithelial cells and numerous lymphocytes as well as dark epithelial cells (stage 2). The medulla of thymuses examined 130 days after GVH induction displayed numerous pale individual epithelial cells and a few pale epithelial cell clusters. Such thymuses also showed a reduction in the number of medullary lymphocytes (stage 3). Finally, the medulla of thymuses 150-160 days after GVH induction displayed numerous pale epithelial cell clusters and Hassall's bodies. These thymuses were indistinguishable from normal adult thymuses (stage 4). All of the animals tested up to day 130 after GVH induction showed no significant T cell function. Animals displaying stage 4 of thymic regeneration showed significant proliferative responses to T cell mitogen, concanavalin A (conA), and six of ten animals also displayed a few plaque forming cells (PFC) to sheep red blood cells (SRBC) in their spleens. Furthermore, all animals (10 of 10) killed on day 180 after GVH induction displayed significant T cell functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Association between the degree of thymic dysplasia and the kinetics of thymic NK cell activity during the graft-versus-host reaction

In this study, by employing different cell doses and parent into F1 hybrid combinations, we have investigated the relationship between the severity of thymic medullary dysplasia and the kinetics of thymic natural killer (NK) cell activity after the induction of graft-versus-host (GVH) reactions. GVH reactions were induced by injecting different doses (30, 20, 10 X 10(6] of C57BL/6 (B6) of A parental lymphoid cells (PLC) into non-X-irradiated adult B6xAF1 (B6AF1) mice. On different days after the induction of GVH reactions, the thymuses were examined histologically and thymocyte NK cell activity was tested by using YAC targets. Our results show that, depending upon the genotype and dose of PLC injected, various degrees of thymic medullary dysplasia (mild, moderate, or severe) can be induced. Furthermore, severe to moderate thymic medullary dysplasia is observed only in those groups of GVH-reactive mice in which thymic NK cell activity occurs early and increases rapidly. In contrast, when mild thymic medullary dysplasia or no thymic alterations was observed, thymic NK cell activity peaked later and was of lower intensity than that of the groups with moderate to severe lesions. These results suggest an association between the degree of thymic medullary dysplasia and the kinetics of NK cell activity in the thymus. Furthermore, the different degrees of thymic medullary dysplasia as described here may serve as a powerful tool to study the role of thymic medullary dysplasia in determining the duration of T-cell immunodeficiency associated with the GVH reactions.

Prevention of murine graft-versus-host disease by inducing and eliminating ASGM1+ cells of donor origin

In this study anti-asialo GM1 antibodies (anti-ASGM1) were used to further characterize the effector cells responsible for graft-versus-host (GVH)-induced histopathological lesions: Two different types of ASGM1+ cells were identified: an endogenous ASGM1+ population and an induced ASGM1+ population. Both of the ASGM1+ cell populations exhibited natural killer (NK) cell activity, as assessed by their ability to lyse YAC tumor targets in vitro. Donor C57BL/6 (B6) mice were treated in vivo with anti-ASGM1 to eliminate endogenous ASGM1+ cells. ASGM1+ cells were induced in B6 donor mice by treating the animals with 15 x 10(6) B6 x AF1 (B6AF1) lymphoid cells for 44-48 hr. The induced ASGM1+ cells were eliminated by in vivo treatment with anti-ASGM1. GVH reactions were induced by injecting B6 lymphoid cells into B6AF1 mice. Prior to GVH induction the B6 donor cells were tested for NK cell activity against YAC tumor target cells in vitro and for T and B cell functions by mitogen responses in vitro. GVH reactions were determined by splenomegaly, suppression of the plaque-forming cell (PFC) response to sheep red blood cells (SRBC), suppression of the T and B cell mitogen responses, and the development of GVH-associated histopathological alterations in the thymus, liver, and pancreas. Donor lymphoid cells depleted of endogenous ASGM1+ cells were effective at inducing splenomegaly, severe suppression of immune functions, and histopathological lesions. Donor lymphoid cells depleted of both the endogenous and induced ASGM1+ cells displayed normal T cell mitogen responses and were capable of inducing splenomegaly and partial suppression of the PFC response to SRBC when injected into B6AF1 recipients, however, these lymphoid cells failed to induce both GVH-associated histopathological lesions and severe suppression of T and B cell mitogen responses. These results suggest that semiallogeneic stimulation induces an ASGM1+ population in the donor inoculum that displays NK cell-like function (YAC killing) and that plays a crucial role in inducing GVH-mediated histopathological lesions and severe immunosuppression of both T and B cell responses.

Kinetics of natural killer cell cytotoxicity during the graft-versus-host reaction. Relationship between natural killer cell activity, T and B cell activity, and development of histopathological alterations

The relationships between splenic natural killer (NK) cell cytotoxicity, T and B cell function, and the development of histopathological lesions in the liver and pancreas have been studied during the course of graft-versus-host (GVH) reactions. GVH reactions were induced in (C57BL/6 X A)F1 (B6AF1) hybrids by different doses, (10,20 and 30 X 10(6)) of either parental strain C57/BL6 (B6) or A lymphoid cells. Splenic NK cell cytotoxicity was studied by employing YAC-1, an NK-cell-sensitive target. Splenic T and B cell function were assessed by mitogen responsiveness to concanavalin A, phytohemagglutinin, and Escherichia coli lipopolysaccharide, and by the in vitro plaque-forming cell response to sheep red blood cells. Histopathological lesions characteristic of GVH reactions were recognized at a time (day 8 after GVH induction) when both T and B cell functions were totally suppressed and NK cell activity was greatest. The severity of histopathological alterations later (day 16 after GVH induction) correlated with an early peak in NK cell cytotoxicity rather than with the overall NK cell activity. When low doses (10,20 X 10(6)) of B6 cells were employed to induce GVH reactions, a significant increase in NK cell activity was observed, yet neither histopathological alterations nor suppression of T and B cell functions were observed. The killing of YAC-1 targets by splenocytes obtained from the different GVH combinations could not be abrogated by pretreatment with anti-Thy 1.2 serum plus complement, suggesting that T lymphocytes were not central to this cytolytic process. These experiments demonstrated that: (1) an inverse relationship between T and B cell function and NK cell activity was observed early after GVH induction, (2) the severity of histopathological lesions and immunosuppression, as well as the degree of overall augmented NK cell activity, was determined by the dose and genotype of donor cells injected to induce GVH reactions, and (3) GVH-associated moderate-severe lesions occurred only in groups in which NK cell activity peaked early--whereas when NK cell activity peaked later, either mild or no lesions were observed, suggesting that the early rapid increase of NK cell activity may be useful for predicting the severity of GVH pathogenesis.

Graft-versus-host reactions in the beige mouse. An investigation of the role of host and donor natural killer cells in the pathogenesis of graft-versus-host disease

To investigate the role of natural killer (NK) cells in the induction and pathogenesis of graft-versus-host (GVH) disease, +/beige (+/bg; normal NK cell activity) and beige/beige (bg/bg; deficient NK cell activity) parental C57BL/6 (B6) lymphoid cells were used to induce GVH reactions in either B6 X C3H/Hej +/bg (+/bgF1) or B6 X C3H/HeJF1 bg/bg (bg/bg F1) hybrid mice. When B6 bg/bg parental lymphoid cells (PLC) were injected into bg/bg F1 mice, early splenomegaly, early severe suppression of the plaque-forming cell (PFC) response to sheep red blood cell (SRBC), and only partial suppression of T cell mitogen responses to concanavalin A (Con A) and phytohemagglutin (PHA) were observed on day 12 after GVH induction. In the same GVH combination, slightly augmented NK cytotoxic activity was induced and no GVH-induced moderate-to-severe pathological alterations in the liver and pancreas were observed. When bg/bg PLC were injected into +/bg F1 mice, early splenomegaly and pronounced immunosuppression of the PFC response to SRBC and partial suppression of Con A and PHA responses were observed on day 12 after GVH induction. In this combination (bg/bg----+/bg F1), significant NK cell activity was induced, but no moderate-to-severe histopathological alterations were observed. In contrast, when B6 +/bg PLC were injected into either +/bg F1 or bg/bg F1 hybrids, early splenomegaly, and severe immunosuppression of both the PFC response to SRBC and the T cell mitogen responses to Con A and PHA were observed by day 12--which persisted until day 30 after GVH induction. Furthermore, high NK cell activity was recorded and moderate-to-severe histopathological alterations appeared in both +/bg F1 and bg/bg F1 recipients. These results show that the bg/bg PLC can induce GVH-associated early splenomegaly and immunosuppression of the PFC response to SRBC in both the bg/bg F1 and +/bg F1 hybrids, but that it failed to induce moderate-to-severe histopathological alterations, even though NK cell activity of host origin was activated during GVH reactions. Conversely, when +/bg donor cells were used to induce the GVH reaction, splenomegaly and immunosuppression, as well as moderate-to-severe histopathological lesions were induced. These results suggest that donor NK cells rather than host NK cells play an active role in GVH-associated tissue damage, which in turn contributes to the long-term suppression.

Suppression of B lymphocyte genesis in the bone marrow by systemic graft-versus-host reactions

The effects of systemic graft-versus-host (GVH) reactions on B lymphocyte production in the bone marrow of mice were examined by quantitating populations of pre-B cells and B lymphocytes. Acute and chronic GVH reactions were induced by injecting A strain lymphoid cells into either (C57BL/6 X A) F1 or (CBA X A) F1 mice, respectively. Control groups of F1 hybrid mice were given syngeneic lymphoid cells. By double immunofluorescence labeling for cytoplasmic mu heavy chains of IgM (c mu) and for surface mu (s mu) the absolute numbers of pre-B cells (c mu + s mu-) and B lymphocytes (s mu +) in the bone marrow and spleen were determined. During acute GVH reactions, the pre-B cells and B lymphocytes in the bone marrow fell rapidly in numbers and were almost absent from 16 days until the end of the 30-day experimental period. In the spleen, the number of B lymphocytes remained normal for 8 days, then fell to less than 2% of control values from 16 days onward. A similar initial decline in pre-B cells and B lymphocytes occurred during chronic GVH reactions. In long-term survivors of GVH reactions, pre-B cells and B lymphocytes began to reappear after 40 days and maintained normal numbers from 100 to 150 days. The antibody response of spleen cells to sheep red blood cells was lost during GVH reactions. However, this occurred even before B lymphocytes were eliminated and the response remained subnormal after B lymphocyte numbers had recovered. The results demonstrate that systemic GVH reactions markedly depress the normally active genesis of primary B lymphocytes in the bone marrow of the host, accounting in part for the associated state of humoral immunodeficiency.

The effects of polyinosinic:polycytidylic acid (pI:C) on the graft-vs-host (GVH) reaction. II. Increased NK-mediated rejection on C57BL/6 lymphocytes by (C57BL/6 X A)F1 mice

We previously demonstrated that treatment of (C57BL/6 X A)F1 (F1) recipient mice with polyinosinic:polycytidylic acid (pI:C) before injection with 30 X 10(6) C57BL/6 (B6) lymphocytes prevents both the immunosuppression and pathologic lesions typical of graft-vs-host (GVH) reactions. We now report the further characterization of this phenomenon. Donor spleen and lymph node cells were labeled with fluorescein in vitro and injected into pI:C-treated or untreated mice. Two days later, recipient splenocytes were analyzed for the presence of fluorescein-labeled donor cells by flow microfluorometry. Treatment of F1 mice with pI:C resulted in a sharp reduction in the recovery of labeled B6 but not A strain parental cells. Treatment with pI:C had no effect when syngeneic recipients were used, or when F1 cells were injected into A, B6, or F1 recipients. These results suggest that pI:C treatment induces rejection of B6 but not A or F1 lymphocytes by F1 hybrid mice at least as early as 2 days after donor cell transfer. As F1 cells are not rejected by either parent, rejection does not seem to be directed against classical alloantigens. These observations are compatible with the previously described model of hybrid resistance (HR) against bone marrow grafts. The rapidity of rejection strongly suggested that natural cytotoxic mechanisms were involved, thus, natural killer (NK) cell and macrophage (M phi) cytotoxic activities were tested throughout the time when the parental cell graft was being rejected. Over this period, pI:C treatment increased cytotoxic activity against the NK-sensitive target cell line YAC-1 but had no effect on spontaneous M phi tumoricidal activity against the L5178Y and MDAY-D2 cell lines. The results suggest that NK cells, but not M phi, may be involved in the elimination of B6 parental cells by the pI:C-treated F1 mice. NK cells have been demonstrated to be radioresistant; thus, as a test of our hypothesis, we examined the effects of irradiation on the capacity of pI:C treated F1 mice to reject B6 lymphocytes. The results show that this capacity was not blocked by 750 cGy, a dose of radiation that abrogates most T and B cell functions. Furthermore, rejection of parental cells could be prevented by treatment of recipient F1 mice with antibodies to asialo GM1, a treatment that suppresses NK activity. These data demonstrate that pI:C-mediated protection from GVH-induced changes is due to increased rejection of grafted B6 parental cells by F1 NK cells, a phenomenon very similar, if not identical, to HR to bone marrow grafts.

The effects of polyinosinic:polycytidylic acid (pI:C) on the graft-vs-host (GVH) reaction. II. Increased NK-mediated rejection on C57BL/6 lymphocytes by (C57BL/6 X A)F1 mice

We previously demonstrated that treatment of (C57BL/6 X A)F1 (F1) recipient mice with polyinosinic:polycytidylic acid (pI:C) before injection with 30 X 10(6) C57BL/6 (B6) lymphocytes prevents both the immunosuppression and pathologic lesions typical of graft-vs-host (GVH) reactions. We now report the further characterization of this phenomenon. Donor spleen and lymph node cells were labeled with fluorescein in vitro and injected into pI:C-treated or untreated mice. Two days later, recipient splenocytes were analyzed for the presence of fluorescein-labeled donor cells by flow microfluorometry. Treatment of F1 mice with pI:C resulted in a sharp reduction in the recovery of labeled B6 but not A strain parental cells. Treatment with pI:C had no effect when syngeneic recipients were used, or when F1 cells were injected into A, B6, or F1 recipients. These results suggest that pI:C treatment induces rejection of B6 but not A or F1 lymphocytes by F1 hybrid mice at least as early as 2 days after donor cell transfer. As F1 cells are not rejected by either parent, rejection does not seem to be directed against classical alloantigens. These observations are compatible with the previously described model of hybrid resistance (HR) against bone marrow grafts. The rapidity of rejection strongly suggested that natural cytotoxic mechanisms were involved, thus, natural killer (NK) cell and macrophage (M phi) cytotoxic activities were tested throughout the time when the parental cell graft was being rejected. Over this period, pI:C treatment increased cytotoxic activity against the NK-sensitive target cell line YAC-1 but had no effect on spontaneous M phi tumoricidal activity against the L5178Y and MDAY-D2 cell lines. The results suggest that NK cells, but not M phi, may be involved in the elimination of B6 parental cells by the pI:C-treated F1 mice. NK cells have been demonstrated to be radioresistant; thus, as a test of our hypothesis, we examined the effects of irradiation on the capacity of pI:C treated F1 mice to reject B6 lymphocytes. The results show that this capacity was not blocked by 750 cGy, a dose of radiation that abrogates most T and B cell functions. Furthermore, rejection of parental cells could be prevented by treatment of recipient F1 mice with antibodies to asialo GM1, a treatment that suppresses NK activity. These data demonstrate that pI:C-mediated protection from GVH-induced changes is due to increased rejection of grafted B6 parental cells by F1 NK cells, a phenomenon very similar, if not identical, to HR to bone marrow grafts.

The effects of polyinosinic: polycytidylic acid (pI:C) on the GVH reaction: immunopathological observations

The effects of polyinosinic: polycytidylic acid (pI:C) on the graft-versus-host (GVH) reaction were studied. The drug pI:C rapidly and markedly induces interferon and augments natural killer (NK) cell activity. GVH reactions were induced by injecting parental lymphoid cells intravenously into F1 hybrid mice. The development of a GVH reaction was monitored by measuring the plaque-forming cell (PFC) response to sheep red blood cells (SRBC) and by histological examination. When 30 X 10(6) B6 lymphoid cells were injected into B6AF1 mice, the recipients developed profound immunosuppression by 10-12 days post-GVH induction. In addition, pathological changes indicative of GVH reactions were seen in the spleen, lymph nodes, thymus, liver, lung, pancreas, and salivary gland of these mice. However, the treatment of B6AF1 recipients with pI:C prior to parental cell transfer markedly reduced the degree of suppression of the immune response, as measured by the PFC response to SRBC. Also, such mice failed to demonstrate the histological lesions of GVH disease. Treatment of donor mice with pI:C had no effect in preventing either GVH-induced immunosuppression or pathological changes. This study suggests that a pI:C-induced mechanism, possibly involving NK cells, is capable of regulating the GVH reaction.

The graft-versus-host reaction and immune function. III. Functional pre-T cells in the bone marrow of graft-versus-host-reactive mice displaying T cell immunodeficiency

Studies were performed to determine whether pre-T cells develop normally in the bone marrow of mice displaying thymic dysplasia and T cell immunodeficiency as a consequence of a graft-versus-host (GVH) reaction. GVH reactions were induced in CBAxAF1 mice by the injection of A strain lymphoid cells. To test for the presence of pre-T cells in GVH-reactive mice, bone marrow from GVH-reactive mice (GVHBM) was injected into irradiated syngeneic F1 mice and 30-40 days later thymic morphology and function were studied. Morphology studies showed nearly normal thymic architectural restoration; moreover, such glands contained normal numbers of Thy-1-positive cells. Functional pre-T cells were evaluated by transferring thymocytes from the irradiated GVHBM-reconstituted mice into T-cell-deprived mice. These thymocytes reconstituted allograft reactivity, T helper cell function and Con A and PHA mitogen responses of T-cell-deprived mice. These results suggest that the pre-T cell population in the bone marrow is not affected by the GVH reaction. Therefore, the T cell immunodeficiency associated with the GVH reaction is not due to a deficiency of pre-T cells in the bone marrow but is more likely associated with GVH-induced thymic dysplasia.

The graft-versus-host reaction and immune function. IV. B cell functional defect associated with a depletion of splenic colony-forming units in marrow of graft-versus-host-reactive mice

Studies were conducted to determine whether a functional B cell defect occurred in the bone marrow of mice experiencing a GVH reaction (GVHBM). GVH reactions were induced in AxCBA F1 adult mice by an injection of A strain lymphoid cells. The GVH reaction was confirmed by immunosuppression and thymus histology. At various intervals after GVH induction, GVHBM was tested for its ability to restore B cell function in adult thymectomized irradiated mice reconstituted with normal thymocytes. GVHBM cells obtained seven days after GVH induction restored but slightly the plaque forming cell (PFC) response to sheep erythrocytes and the mitogen response to lipopolysaccharide (LPS). GVHBM cells obtained 10 days or later failed to reconstitute the PFC or LPS responses. GVHBM cells suppressed neither the T or B cell function of normal spleen cells nor the LPS mitogen response of normal bone marrow cells. In addition, the splenic colony-forming units (CFU-s) in GVHBM were slightly decreased by day 10 after GVH induction and markedly depressed by day 22 after GVH induction. These results suggest that the GVH reaction may affect two different events in B cell differentiation. The early decrease in functional B cells that occurs before there is any change in the CFU-s population suggests a direct effect on B cell production, whereas the later absence of functional B cells could be due to the marked decline in stem cell production (CFU-s).

The functional and histological basis for graft-versus-host-induced immunosuppression

The GvH reaction resulting from the injection of parental strain cells into adult F1 hybrids suppresses both cell-mediated and humoral immune responses and is dependent on the donor-host combination and the number of parental cells used to induce the GvH reaction. The early suppression is due, at least in part, to the increased number of macrophages and the activation of suppressor macrophages which act directly on the T-helper cell and perhaps the B-cell as well. The macrophage suppression is associated with an increase in PGE production. The long-term T-cell immunodeficiency is mediated by GvH-induced thymic dysplasia resulting in a block or an arrest in T-cell differentiation and deficient IL-2 production. The B-cell immunodeficiency is associated with both a decrease in B-cell production from lymphoid progenitors and a decrease in CFU-s production. The GvH reaction induces 2 types of thymic lesion, a stress-related effect causing atrophy of the thymic cortex and a cytolytic process causing severe-to-moderate lesions in the thymic medulla as a consequence of injury to medullary epithelial cells and a loss of Hassall's corpuscles (thymic dysplasia). By employing the NK-cell-deficient beige mutation, it was shown that the severe-to-moderate thymic medullary lesions occurred in F1 mice only in those transplant situations in which the donor inoculum was of the +/bg genotype, regardless of the genotype of the recipient. It is proposed that activation of parental T cells may contribute to the early immunosuppressive events; however, the relatively permanent immunosuppression appears to be associated with NK-like effector cells which are capable of causing injury to lymphoid and epithelial tissue, especially epithelium of the thymic medulla. These studies raise the possibility that the GvH reaction may contribute to some T- and B-cell immunodeficiencies observed in the SCID and AIDS syndromes, as well as in patients following bone marrow transplantation.

Interleukin-1 and interleukin-2 defects associated with murine graft-versus-host-induced immunodeficiency

In this study we investigated the mechanism, or mechanisms, involved in graft-versus-host (GVH)-induced T cell immunodeficiency. Chronic GVH reactions were induced in normal CBA X A F1 (BAF1) hybrid mice by the injection of parental A strain lymphoid cells. At various times (43-91 days) after GVH induction, the functional status of GVH T cells was assessed using interleukin-1 (IL-1) and interleukin-2 (IL-2) as probes. The response of GVH thymocytes to IL-1 was depressed when compared with normal thymocytes. Although GVH peanut-agglutinin-negative (PNA-) thymocytes did respond to IL-2 alone or IL-2 plus phytohemagglutinin (PHA), this response was significantly lower than the response of PNA- thymocytes from normal mice. In addition, GVH spleen cells failed to produce significant amounts of IL-2 when stimulated with concanavalin A. These results suggest that the long term immunosuppression associated with murine chronic GVH disease is due, at least in part, to a decrease in the responsiveness to IL-1 and IL-2, and to a marked deficiency in IL-2 production.

Stimulation of the murine mixed leukocyte reaction: optimal proliferation of responders requires activation of stimulators

In characterizing the functional properties of the stimulators in a mixed leukocyte reaction (MLR) we have established that the optimally effective stimulators must themselves be capable of undergoing the early stages of proliferative activation. We treated the stimulators with sublytic doses of a variety of agents (ouabain, ultra-violet radiation, 5-fluorouracil and colchicine), which have been reported to inhibit their stimulating capacity, and then in parallel experiments, we examined the treated cells for their capacity to stimulate allogeneic cells and their ability to respond to Con A. A direct correlation was found between the capacity of mitomycin C-treated splenocytes to stimulate allogeneic cells in an MLR and their ability to undergo changes characteristic of pre-S phase activation, namely, increases in K+ influx and in cell size, in response to Con A. This correlation also existed in the case of metabolically active but immunosuppressed splenocytes from mice undergoing late graft-versus-host (GVH) reaction: these cells did not show increase in potassium influx in response to Con A and their stimulating ability was inhibited. Using fluorescein labelled anti-Thy 1.2 as a marker for T cells in the stimulating population, it was shown that a considerable fraction (up to one third) of the blasts in a mixed leukocyte culture (MLC) originated in the mitomycin C-treated stimulating population. These data are consistent with the hypothesis that induction of maximal proliferation, in MLR, requires that certain of the cells (mainly T cells) of the stimulating population undergo the early stages of activation.

Macrophage activity in mice undergoing chronic graft-versus-host reactions

The functional state of the mononuclear phagocyte system has been investigated in mice undergoing chronic graft-versus-host (GVH) reactions (GVHR), initiated by the injection of parental DBA/2 lymphoid cells into (DBA/2 X C57BL/6)F1 hybrid mice. Macrophage function was assessed in vivo by the ability to develop host resistance to infection with Listeria monocytogenes and found to be normal in GVH mice, as measured by the development of resistance during the early phase of natural (macrophage-mediated) resistance to the infection. During the later phase of acquired immunity to listerial infection, GVH mice had lowered resistance, but this was attributed to impaired T cell immunity rather than to defective macrophage function. The inflammatory response to a phlogistic agent, thioglycolate, was also found to be normal in GVH mice, as measured by the accumulation of inflammatory macrophages in the peritoneal cavity. In an in vitro assessment of macrophage function, phagocytosis was found to be enhanced initially (2 weeks following GVHR induction) but it subsequently became depressed for the duration of the study (12 weeks after GVHR induction). Macrophage chemotactic activity was initially normal, then became depressed and remained so for the duration of the study. Thus, despite the profound suppression of specific immunity induced by the GVH reaction and the functional defects of GVH macrophages apparent in vitro, the response of the mononuclear phagocyte system to in vivo stimuli, such as infection or inflammation, is unimpaired in GVH mice.

Mammary carcinoma arising in mice undergoing a chronic graft-versus-host reaction

A graft-versus-host reaction (GVHR) was induced in 30 (CBA X A)F1 mice by the iv injection of 50 X 10(6) parental strain A lymphoid cells. Solid tumors emerged in 5 of 10 experimental animals that survived beyond 14 months after the GVHR was initiated. The neoplasms were judged to be mammary carcinomas by light and electron microscopic examinations. C-type RNA viral structures were observed in some tumor cells. The neoplasms were successfully transplanted into syngeneic animals by either sc or ip injections of tumor cell suspensions. Tumor transfer to syngeneic mice was not possible if only spleen cells from tumor-bearing animals were transferred. No tumors developed in an age-matched control group that received no treatment.

Precocious thymic involution manifest by epithelial injury in the acquired immune deficiency syndrome

Thymuses from six heterosexual Haitian patients with the acquired immune deficiency syndrome (AIDS) were studied by light microscopy and the findings were compared with those from three control groups. The control groups included 1) five age-matched Haitian hospital patients; 2) ten age- and sex-matched Montreal patients who had died suddenly or had had brief illnesses; and 3) 20 middle-elderly Montreal patients who had experienced chronic, wasting illnesses or prolonged hospitalization. Thymuses from patients with AIDS demonstrated pronounced involution, effacement of the cortex and medulla, marked thymocyte depletion, variable degrees of plasma cell infiltration and fibrosis, and, above all, absence of Hassall's corpuscles. Thymuses from Haitian and Montreal control subjects who had died suddenly or had brief illnesses demonstrated minimal involution and abundant Hassall's corpuscles. Although thymuses from 12 of the chronically ill control subjects demonstrated marked involution, architectural effacement, and absence of Hassall's corpuscles, partial architectural preservation and variable numbers of Hassall's corpuscles were observed in eight of these subjects. Thus, the extent of thymic involution observed in patients with AIDS antedates that incurred with aging and supersedes that induced by sustained stress and inanition. The loss of Hassall's corpuscles in patients with AIDS suggests that the thymic epithelium either incurs a form of injury or undergoes precocious involution during the illness. Whether this lesion is central to the pathogenesis of AIDS or merely a reflection of intense, sustained stress coupled with accelerated physiologic involution is unknown. It is possible that the disappearance of Hassall's corpuscles may indicate important, although as yet cryptic events within the thymic microenvironment in this syndrome.

The graft-versus-host reaction and immune function. I. T helper cell immunodeficiency associated with graft-versus-host-induced thymic epithelial cell damage

The injection of parental A strain lymphoid cells into adrenalectomized CBAxA F1 (BAF1) mice induced a chronic graft-versus-host (GVH) reaction resulting in T cell and B cell immunosuppression as well as thymic epithelial cell injury, but not stress-related thymic involution. Thymocytes from BAF1 mice undergoing a GVH reaction were studied for their ability to reconstitute T helper cell (TH) function and phytohemagglutinin (PHA) and concanavalin A (Con A) mitogen responses in thymectomized, irradiated, BAF1 mice reconstituted with normal syngeneic bone marrow (ATxBM). Thymocytes from BAF1 mice early after the induction of a GVH reaction (days 10-12) were as effective as normal thymocytes in reconstituting TH and mitogen responses. Thymocytes from BAF1 mice 40 or more days after the induction of a GVH reaction did not reconstitute either the TH function or PHA and Con A responses in ATxBM mice. The inability to reconstitute ATxBM mice was not due to the presence of suppressor cells contained in the thymocyte inoculum. It is proposed that GVH-induced thymic epithelial cell injury blocks or arrests normal T cell differentiation, resulting in a population of thymocytes that lack the potential to become competent T helper cells or mitogen-responsive cells when transferred into ATxBM mice. This thymic functional defect results in a permanent TH immunodeficiency in mice experiencing a chronic GVH reaction.

The graft-versus-host reaction and immune function. II. Recruitment of pre-T-cells in vivo by graft-versus-host-induced dysplastic thymuses following irradiation and bone marrow treatment

The graft-versus-host (GVH) reaction induces thymic dysplasia and an arrest in T cell differentiation. Studies were performed to test the effect of irradiation and reconstitution with bone marrow on GVH-induced thymic dysplasia and T cell differentiation. GVH reactions were induced in CBAxAF1 adult mice by the injection of A strain lymphoid cells. All GVH-reactive mice were immunosuppressed by day 7 after GVH induction and thymic dysplasia was evident by day 24. Forty days after the induction of the GVH reaction the mice were irradiated (850 rads) and repopulated with 10-15 X 10(6) syngeneic or parental bone marrow cells. Thirty days after irradiation and bone marrow reconstitution, GVH-reactive mice were used for histological and functional studies. These mice displayed near-normal thymus morphology with scattered epithelial cells in the medulla, and normal numbers of Thy-1-positive cells. Donor cells had totally repopulated thymuses of irradiated bone marrow reconstituted mice by day 19 after irradiation. T helper cell function did not recover in the reconstituted mice. These results suggest that (1) the process responsible for GVH-induced thymic dysplasia is radiosensitive, and (2) the thymus has the potential to regenerate a normal structure, but fails to regain normal function.