Nitric oxide mediates immune dysfunction in the spontaneously hypertensive rat

The immune system of the spontaneously hypertensive rat is dysfunctional compared with that of normotensive control strains. Previous studies from our laboratory have shown that immunodepression in the spontaneously hypertensive rat was mediated by macrophages. The current study examines the mechanism for the depressed proliferative responses to concanavalin A typically observed by splenic mononuclear cells of spontaneously hypertensive rats. We tested various inhibitors of known macrophage products responsible for suppressing lymphoid function. The nitric oxide synthetase inhibitor NG-monomethyl L-arginine produced dose-dependent derepression of the proliferative responses of splenic mononuclear cells to concanavalin A. In contrast, indomethacin and catalase exhibited only weak derepression of the proliferative responses. Subsequent analysis showed that splenic mononuclear cells from spontaneously hypertensive rats generated greater nitric oxide levels than cells from Wistar-Kyoto rats, and nitric oxide levels were reduced when the inhibitor was added to splenic mononuclear cell cultures from spontaneously hypertensive rats. We further demonstrated that L-arginine is required for the development of the depressed mitogen-induced proliferative responses in these cells. Addition of L-arginine in excess of 10 microM to cultures diminished cell proliferation and increased nitric oxide. Polyclonal antibodies to murine interferon gamma reduced nitric oxide accumulation by approximately 50%, suggesting that interferon gamma is partially responsible for enhancing nitric oxide production in mitogen-stimulated splenic mononuclear cell cultures from spontaneously hypertensive rats. Thus, this study provides evidence that the immune depression observed in the spontaneously hypertensive rat is nitric oxide dependent.

Spontaneously hypertensive rat: lymphoid depression is age dependent and mediated via a mononuclear cell subpopulation

Immune dysfunction has been reported in spontaneously hypertensive rats (SHR), particularly in mature animals with established hypertension. The current study examined the time course of development of immune dysfunction and defined its cellular basis in male SHR and control normotensive Wistar-Kyoto rats (WKY). Mitogen-induced proliferative responses in lymphoid cells obtained from induced proliferative responses in lymphoid cells obtained from SHR thymus and spleen before (age 4 wk) and during the development of (ages 8 and 12 wk) hypertension and in age-matched normotensive WKY were monitored. A 50% reduction in concanavalin A (Con A)-induced proliferative responses was seen in SHR thymocytes compared with those of WKY at 12 wk only, suggesting differences in immature T-cell populations. Con A-induced T-cell proliferative responses in splenocytes also differed between strains: greatest (as much as 8-fold) decreases were found in 12-wk-old SHR. Similar findings were obtained in splenocytes stimulated with lipopolysaccharide (LPS), indicating differences in B-cell function. Mononuclear cells depleted of their adherent cell population were prepared from SHR and WKY at 12+ wk of age and assayed for their proliferative responses to LPS and Con A. The remaining nonadherent mononuclear cells of SHR had proliferative responses equal to or greater than those of WKY. Further, when SHR splenic mononuclear cells were allowed to adhere to plastic, and the adherent fraction was co-cultured with either SHR G-10 nonadherent or unfractionated SHR splenic mononuclear cells, proliferative responses were suppressed by as much as 88%.(ABSTRACT TRUNCATED AT 250 WORDS)