Some effects of silical treatment on Marek's disease.

Treatment of newly hatched chicks with silica by the intraperitoneal route delayed the onset of mortalities due to the JM strain of Marek's disease (MD' virus inoculated at 6 days of age. During the 88-day observation period fewer silica-treated chicks died of MD, but this difference was not usually statistically significant. Silica treatment had no effect on the susceptibility of 4-week-old birds. Silica treatment reduced the antibody response to MD but, in general, not significantly. The antibody response to bovine serum albumin was significantly enhanced if measured by the indirect hemagglutination test but not if measured by the agar gel diffusion test, whereas the response to Brucella abortus was enhanced significantly in N-line (MD-resistant) chicks but not significantly in P-line (MD-susceptible) chicks. Five days after infection, silica-treated chicks had significantly less fluorescing antigen in thymus and bursa than did untreated chicks; no difference was observed in the spleen. After silica treatment the glass-adherent cell population in the buffy coat was increased by up to 10-fold compared with untreated chicks. It is suggested that silica treatment induced macrophage proliferation, with subsequent restriction of MD virus spread, yet allowed an adjuvant-type effect with other antigens.