Studies on autoimmunity for initiation of beta-cell destruction. V. Decrease of macrophage-dependent T lymphocytes and natural killer cytotoxicity in silica-treated BB rats.

Administration of silica, which is selectively toxic to macrophages, to young BB rats resulted in the prevention of insulitis and diabetes. However, the mechanism leading to the prevention of an autoimmune process in silica-treated BB rats is not known. This study was undertaken to investigate the mechanism involved in prevention of insulitis and diabetes. Neonates of diabetes-prone BB (DPBB) rats injected with concanavalin A (ConA)-activated spleen cells from silica-treated DPBB (STDPBB) rats did not develop insulitis or diabetes, whereas DPBB neonates injected with ConA-activated spleen cells from the untreated DPBB rats developed both insulitis and diabetes. Not only was there a decrease of natural killer (NK) cell activity in splenocytes from STDPBB rats, but there was also a significant reduction in the number of immunocytes such as T lymphocytes (helper/inducer and cytotoxic/suppressor) and NK cells. The number of macrophages in both spleen and peripheral blood was significantly decreased in STDP rats compared with untreated DP rats. In contrast to the changes in T lymphocytes and NK cell activity, there was no change in target beta-cells in STDPBB rats with regard to the susceptibility to adoptive transfer of insulitis. It is concluded that the prevention of insulitis and diabetes in STDPBB rats is due to a decrease in macrophage-dependent T lymphocytes and NK cell cytotoxicity.