Studies on the roles of T helper type I and type II cytokines in HIV immunopathogenesis: Role and regulation of interleukin-10.
Creators: name: Daftarian, Mohammad Pirouz.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1997
Subjects: subject: Health Sciences, Immunology.

description: Infection of immune cells with human immunodeficiency virus (HIV) induces dysregulation of cytokines which may play a vital role in HIV pathogenesis. I analyzed the expression of Th1 (interferon-$\gamma,$ (IFN-$\gamma)\rbrack$ and Th2 (interleukin-4 (IL-4), IL-10) type cytokines in unstimulated and mitogen stimulated peripheral blood mononuclear cells (PBMC) from HIV seropositive (HIV$\sp+)$ patients. It was determined that IFN-$\gamma$ mRNA in unstimulated PBMC was significantly decreased and IL-10 mRNA as well as IL-10 protein was significantly increased in patients with $$400 CD4$\sp+$ T cells/mm$\sp3$ (n = 6) and normal controls (n = 16). Mitogen stimulation of PBMC revealed two groups of HIV$\sp+,$ low and normal IL-10 producers. Production of IL-4 was reduced in HIV$\sp+$ individuals with $$400 CD4$\sp+$ T cells/mm$\sp3.$ However, ability to produce IFN-y by mitogen stimulated PBMC and CD4 T$\sp+$ cells was not impaired in HIV$\sp+$ individuals. These results suggest that PBMC of HIV$\sp+$ exhibit dysregulation of Th2 type cytokines which may play a role in HIV immunopathogenesis. In the next set of experiments, the IL-10 production was correlated with the levels of proliferative responses to recall antigens. Low IL-10 producers proliferated in response to recall antigens, and demonstrated enhanced recall antigen-induced proliferation upon addition of anti-IL-10 antibodies and/or IL-12. Conversely, normal IL-10 producers had PBMC that failed to proliferate to recall antigens, and did not demonstrate enhanced recall antigen-induced proliferation upon addition of anti-IL-10 antibodies and/or IL-12. Source of the IL-10 production in PBMC of HIV$\sp+$ individuals was shown to be monocytes, while, in HIV controls, it was produced by both T cells and monocytes. The molecular mechanisms underlying the production of IL-10 are not clear. I have demonstrated that monocytes/macrophages are required for IL-10 production by normal activated T cells. IL-10 production was significantly downregulated in both T cell and monocyte depleted PBMC compared to undepleted PBMC, and IL-10 production could be restored following addition of monocyte conditioned medium (MCM), this suggested that IL-10 production by T cells is regulated by monokine(s) produced by activated monocytes. The monokine(s) responsible for IL-10 induction by T cells were further studied. Addition of IL-6 and IL-12 enhanced IL-10 production in monocyte depleted PBMC in a dose dependent and additive manner. With respect to regulation of IL-10 produced by monocytes, tumor necrosis factor $\alpha$ (TNF-$\alpha)$ was found to induce IL-10 production by resting purified monocytes. Taken together, these findings suggest that IL-10 production by human T cells and monocytes is differentially regulated. IL-12 and IL-6 induce the expression of IL-10 by PHA stimulated T cells whereas TNF-$\alpha$ induces IL-10 production by monocytes. Since IL-10 inhibits production of IL-6, IL-12 and TNF-$\alpha,$ these results may indicate a potential mechanism of negative feedback regulation of the immune system. Furthermore, mitogen stimulated PBMC from HIV$\sp+$ individuals produced significantly lower levels of IL-12 than did those from HIV-controls. A defect in IL-12 induction may partially cause IL-10 dysregulation in HIV infection.