Patricia A. L. Kongshavn

The requirement for gamma Interferon in resistance of mice to experimental tularemia

The role of gamma interferon (IFN-gamma) in the host response to experimental tularemia was evaluated in a murine model. C57BL/6 strain mice were given a series of daily intravenous injections of 10(6) units (U) recombinant murine IFN-gamma prior to infection with Francisella tularensis LVS. Three days later, the number of bacteria in the tissues of IFN-gamma-treated mice was found to be less than that in control mice by a factor of 10-20. The effect of IFN-gamma on anti-tularemic resistance was dependent upon the administered dose, with as little as 10(4) U/mouse/day inducing a significant level of enhanced resistance. IFN-gamma was also effective in enhancing resistance to tularemia in the A/J mouse strain which, in comparison with the C57BL/6 strain, is more susceptible to infection. When C57BL/6 mice were treated with a monoclonal antibody directed against murine IFN-gamma, the number of Francisella recovered from their tissues 6 days following infection was increased by as much as 15 times, in comparison with control mice. The results of these experiments clearly indicate that the resolution of experimental murine tularemia is dependent, at least in part, on the participation of IFN-gamma.

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 B6xC3H/Hej +/bg (+/bgF1) or B6°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 phytohemagglutinin (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.

Genetic control of susceptibility of mice to infection with E. histolytica

Summary Genetic susceptibility to Entamoeba histolytica infection in nine inbred strains and one outbred strain of mice was studied. The number of E. histolytica trophozoites in the ceca of the mice was examined 5 days after intracecal inoculation of axenic amoebae. C3H/HeCr, BALB/c, NZB/BIN, BIO.A, DBA/2 and C57BL/6 were susceptible whereas A/J, CE, DBA/1 and CD‐I mouse strains were relatively resistant. Examination of F1 hybrid animals derived from susceptible B10.A and resistant A/J strains of mice showed that susceptibility was dominant over resistance. Segregation analysis of backcross and F2 progeny derived from the same progenitor strains is compatible with the hypothesis that susceptibility to E. histolytica infection in mice is controlled by a single, dominent gene which has been designated Enh. No association was found between the H‐2 haplotype and the trait of susceptibility to amoebiasis, indicating that the major histocompatibility complex does not play a major role in regulating the early phase of the response to infection with E. histolytica.

Enhancing and suppressive effects of tumour necrosis factor/cachectin on growth of Trypanosoma musculi

Summary The effect of human recombinant TNF on the growth of T. musculi has been investigated. When added to parasites cultured in vitro, TNF inhibited their growth. In the presence of thioglycollate‐elicited peritoneal exudate cells, the opposite effect was seen and TNF enhanced the growth of trypanosomes in vitro. Similarly, administration of TNF in vivo during the course of infection led to a net increase in the parasite population. It is suggested that TNF exerts a direct anti‐trypanosomal effect while simultaneously promoting the growth of the parasite through an indirect effect mediated via the hosts cells, possibly the macrophages.

Suppression of in vitro antibody responses by listeria primed spleen cells.

Abstract Spleen cells from mice primed with virulent Listeria monocytogenes do not develop an anti-SRBC plaque forming cell response to SRBC in culture. Furthermore, when Listeria primed spleen cells are co-cultured with normal spleen cells and SRBC, the anti-SRBC response of the normal cells is suppressed. Listeria primed spleen cells from T cell depleted donors are equally effective at immunosuppression. The immunosuppressive effect does not appear to be due to the presence of the bacterium or its products per se in the cultures. Furthermore, the effect cannot be transferred across a 0.45 μm pore membrane. Kinetic studies show that the immunosuppressive effect develops by 2 days post- Listeria inoculation and peaks by Day 6. Low doses of Listeria are not immunosuppressive and produce some enhancement effect. From these results, it is suggested that a population of non-T cell dependent cells develop in Listeria primed hosts that nonspecifically suppress the response of B cells to an unrelated antigen in culture.

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 CBAxA 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.

Protection of mice against intestinal amoebiasis with BCG, Corynebacterium parvum and Listeria monocytogenes

Summary Treatment with Corynebacterium parvum or BCG, or infection with live Listeria monocytogenes was found to protect mice against subsequent infection with Entamoeba histolytica. Complete protection was obtained in mice treated with 107 (colony forming units) of BCG but not with 105. Partial protection was achieved with 106 of BCG. These data provide evidence that non‐specific immunity plays an important role in host defense against amoebic infection

The effect of splenectomy on resistance of mice to Entamoeba histolytica infection

Summary The role of the spleen in amoebic infection was examined in mice, using strains selected as being either genetically‐susceptible (C57BL/6) or genetically‐resistant (A/J) to amoebiasis. Splenectomized and sham‐operated animals were inoculated intracaecally with 2·5 × 105 polyxenic trophozoites of E. histolytica at 6. 12 and 15 days post‐splenectomy. The animals were killed 6 or 12 days after infection and the parasite burden was evaluated. Removal of the spleen in both susceptible and resistant mouse strains rendered these hosts extremely resistant to amoebic infection by this criterion. Gross examination of the caeca of non‐splenectomized, genetically‐susceptible mice showed numerous ulcers over the mucosal surface when compared to the splenectomized group which had superficial lesions or none. These observations suggest that the spleen plays a suppressive role in early anti‐amoebic resistance.

Cellular mechanisms of resistance to Listeria monocytogenes.

Listeria monocytogenes is a facultative intracellular bacterial parasite that can survive and multiply in mammalian macrophages. The infected host has at its disposal several lines of defense, each of which is mobilized in successive steps in the course of listeriosis. It has recently been demonstrated that the key mechanisms underlying successful anti-listerial resistance are genetically regulated. The availability of well-defined inbred mouse strains facilitated greatly the study of host-parasite interaction in listeriosis and it has become obvious that genetic control of host defense processes is simpler than originally anticipated. This review will deal mainly with the mechanisms of natural resistance to Listeria monocytogenes as uncovered in our laboratory using the genetic probe. The newer aspects of acquired resistance to this infection, a process which is now recognized as a classical example of cell-mediated immunity, will also be summarized briefly.

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·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.