Autocrine regulation of IL-12 receptor expression is independent of secondary IFN-gamma secretion and not restricted to T and NK cells

The biological response to IL-12 is mediated through specific binding to a high affinity receptor complex composed of at least two subunits (designated IL-12Rbeta1 and IL-12Rbeta2) that are expressed on NK cells and activated T cells. The selective loss of IL-12Rbeta2 expression during Th2 T cell differentiation suggests that regulation of this receptor component may govern IL-12 responsiveness. In murine assays, down-regulation of IL-12Rbeta2 expression can be prevented by treatment with IFN-gamma, indicating that receptor expression and hence IL-12 responsiveness may be regulated, at least in part, by the local cytokine milieu. In this study, we report that cellular expression of both IL-12Rbeta1 and beta2 mRNA is increased in the lymph nodes of naive mice following systemic administration of murine rIL-12 (rmIL-12). Changes in IL-12R mRNA were associated with increased IFN-gamma secretion following ex vivo activation of lymph node cells with rmIL-12, indicating the presence of a functional receptor complex. Expression of IL-12R mRNA was not restricted to lymph node T cells, and its autocrine regulation was independent of secondary IFN-gamma secretion. Data from fractionated lymph node cells as well as rmIL-12-treated B cell-deficient mice suggest that IL-12-responsive B cells may represent an alternative cellular source for IFN-gamma production. However, the strength of the biological response to rmIL-12 is not governed solely by receptor expression, as rmIL-12-induced IFN-gamma secretion from cultured lymph node cells is accessory cell dependent and can be partially blocked by inhibition of B7 costimulation.

Binding and functional properties of recombinant and endogenous CXCR3 chemokine receptors

IP10 and MIG are two members of the CXC branch of the chemokine superfamily whose expression is dramatically up-regulated by interferon (IFN)-gamma. The proteins act largely on natural killer (NK)-cells and activated T-cells and have been implicated in mediating some of the effects of IFN-gamma and lipopolysaccharides (LPSs), as well as T-cell-dependent anti-tumor responses. Recently both chemokines have been shown to be functional agonists of the same G-protein-coupled receptor, CXCR3. We now report the pharmacological characterization of CXCR3 and find that, when heterologously expressed, CXCR3 binds IP10 and MIG with Ki values of 0.14 and 4.9 nM, respectively. The receptor has very modest affinity for SDF-1alpha and little or no affinity for other CXC-chemokines. The properties of the endogenous receptor expressed on activated T-cells are similar. Surprisingly, several CC-chemokines, particularly eotaxin and MCP-4, also compete with moderate affinity for the binding of IP10 to CXCR3. Eotaxin does not activate CXCR3 but, in CXCR3-transfected cells, can block IP10-mediated receptor activation. Eotaxin, therefore, may be a natural CXCR3 antagonist.

Regulation of the inflammatory response in animal models of multiple sclerosis by interleukin-12

Interleukin 12 (IL-12), a novel heterodimeric protein produced primarily by antigen-presenting cells, serves as a key regulator of innate and adaptive immune responses. In addition to being a potent inducer of IFN-gamma, IL-12 is widely considered to be the principal cytokine that regulates the generation of Th1 type effector cells. As the successful induction of experimental autoimmune encephalomyelitis (EAE) is associated with a strong Th1 type cellular response, we have evaluated the role of IL-12 in regulating the pathogenesis of EAE in SJL/J mice and Lewis rats. In both settings, treatment with IL-12 was found to accelerate the onset and increase the severity and duration of clinical disease. More importantly, administration of IL-12 to Lewis rats that had recovered from primary disease was found to trigger clinical relapse. In all instances, IL-12-induced exacerbation was associated with a profound increase in iNOS positive macrophages within the perivascular lesions. Although IL-12-induced IFN-gamma does not appear to be required for exacerbation of disease, neutralizing antibodies against murine IL-12 delay the onset and reduce the severity of adoptively transferred EAE, indicating a role for endogenous IL-12 as regulator of disease. Based on the above findings, effective inhibition of IL-12 in vivo may have great therapeutic value in the treatment of MS and other Th1-associated inflammatory disorders.

Immunoregulation by interleukin-12 in MB49.1 tumor-bearing mice: cellular and cytokine-mediated effector mechanisms

Administration of recombinant murine interleukin (rmIL)-12 to MB49.1 tumor-bearing mice results in dose-dependent regression of the primary tumor and the generation of protective antitumor immunity in the majority of animals. rmIL-12 administration is associated with a marked increase in lymph node cellularity that is predominantly due to the expansion of B220+ B cells as well as CD8+ T cells. Stimulation of lymph node cells from rmIL-12-treated, but not control tumor-bearing mice, with MB49.1 tumor cells in vitro was shown to enhance the secretion of interferon (IFN)-gamma. The magnitude of this in vitro response was dependent on the dose of rmIL-12 administered in vivo and mirrored the change in circulating serum IFN-gamma. Furthermore, at the height of the in vitro response to tumor stimulation, the addition of a neutralizing antibody to murine IL-12 suppressed IFN-gamma production, indicating a role for endogenous IL-12 in this antigen-specific cytokine response. Although studies in SCID mice confirmed that an appropriate T cell response was required for rmIL-12-mediated antitumor activity, in immunocompetent animals early tumor regression was not accompanied by cellular infiltration of the tumor. In contrast, a profound increase in tumor-associated inducible nitric oxide synthase (iNOS) was observed in mice receiving rmIL-12 which preceded T cell infiltration of the tumor which could be detected during the second week of IL-12 treatment. Direct tumor killing through the cytotoxic actions of NO via the iNOS pathway may serve as a way of generating tumor antigen which enables the host to mount a subsequent T cell response against the tumor.

Regulation of experimental autoimmune encephalomyelitis by interleukin-12

We have evaluated the effects of rmIL-12 on the course of adoptively transferred EAE. When mice were injected with LNC that had been stimulated in vitro with PLP in the presence of rmIL-12, the subsequent course of disease was more severe and prolonged than controls. In vitro stimulation with PLP in the presence of IL-12 was associated with an increase in IFN-gamma and decrease in IL-4-producing cells, indicating a preferential expansion of Th1 effector cells. At peak disease, no notable differences in either the cellular composition or cytokine expression within CNS lesions was seen between groups. However, the frequency of macrophages that stained positively for inducible nitric oxide synthase (iNOS) was increased in animals challenged with rmIL-12 treated LNC. These data suggest that in addition to promoting the preferential expansion of IFN-gamma-producing cells by rmIL-12 treatment in vitro, in vivo effects leading to macrophage activation and iNOS expression may contribute to the severe, protracted course of CNS inflammation in this model. In contrast, treatment of mice with an antibody to murine IL-12 following cell transfer completely prevented paralysis with only 40% of the mice developing mild disease. These data suggest that endogenous IL-12 plays a pivotal role in the pathogenesis of this model of autoimmune disease.

Adoptive transfer of experimental allergic encephalomyelitis after in vitro treatment with recombinant murine interleukin-12. Preferential expansion of interferon-gamma-producing cells and increased expression of macrophage-associated inducible nitric oxide synthase as immunomodulatory mechanisms

In an adoptive transfer model of experimental allergic encephalomyelitis, stimulation of lymph node cells with proteolipid protein and recombinant murine interleukin (rmIL)-12 before cell transfer accelerated the onset and exacerbates clinical disease. In vitro stimulation with proteolipid protein in the presence of rmIL-12 was associated with an increase in interferon-gamma-producing cells and a decrease in IL-4-producing cells, indicating a preferential expansion of Th1 effector cells. This was supported by the finding that severe disease with rapid onset could be transferred with as few as 10 x 10(6) rmIL-12-stimulated lymph node cells. Immunohistochemical analysis confirmed that the accelerated onset of disease after in vitro stimulation with rmIL-12 coincided with an acute inflammatory response in the central nervous system. At peak disease, both control and rmIL-12 treatment groups exhibited extensive cellular infiltration with characteristic perivascular cuffing. No notable differences in either the cellular composition or cytokine expression within the lesions were seen between groups. However, the frequency of macrophages that stained positively for inducible nitric oxide synthase was increased in animals challenged with rmIL-12-treated lymph node cells. The results suggest that, in addition to promoting the preferential expansion of interferon-gamma-producing cells by rmIL-12 in vitro, secondary in vivo effects leading to macrophage activation and inducible nitric oxide synthase expression may contribute to the severe and protracted course of central nervous system inflammation in this model.

Prevention of experimental autoimmune encephalomyelitis by antibodies against interleukin 12

Experimental allergic encephalomyelitis (EAE) is an autoimmune disease of the central nervous system that can be transferred to naive mice via CD4+ T cells isolated from appropriately immunized mice. We have evaluated the effects of recombinant murine interleukin 12 (rmIL-12), a potent inducer of interferon gamma (IFN-gamma) and promoter of Th1 T cell development, on the course of adoptively transferred EAE. The transfer of lymph node cells (LNC) isolated from proteolipid protein (PLP)-primed animals and stimulated in vitro with PLP to naive mice resulted in a progressive paralytic disease culminating in complete hind limb paralysis in the majority of the recipients. When mice were injected with LNC that had been stimulated in vitro with PLP in the presence of rmIL-12, the subsequent course of disease was more severe and prolonged. The addition of rmIL-12 during the in vitro stimulation with PLP resulted in a 10-fold increase in IFN-gamma and a 2-fold increase in tumor necrosis factor (TNF) alpha in the supernatants, relative to LNC stimulated with PLP alone. However, neutralization of IFN-gamma or TNF-alpha in vitro with specific antibodies did not abrogate the ability of rmIL-12 to exacerbate the subsequent disease. Similarly, mice treated with rmIL-12 in vivo after the transfer of antigen-stimulated LNC developed a more severe and prolonged course of disease compared with vehicle-treated control animals. In contrast, treatment of mice with an antibody to murine IL-12 after cell transfer completely prevented paralysis, with only 40% of the mice developing mild disease. These results demonstrate that in vitro stimulation of antigen primed LNC with PLP and rmIL-12 enhances their subsequent encephalitogenicity. Furthermore, inhibition of endogenous IL-12 in vivo after LNC transfer prevented paralysis, suggesting that endogenous IL-12 plays a pivotal role in the pathogenesis of this model of autoimmune disease.