Relationship of phagocytic activity to pathogenicity of mouse hepatitis virus as affected by triolein and cortisone.

The pathogenicity of mouse hepatitis virus (MHV-1) was studied following treatment with triolein and cortisone which, respectively, stimulated and suppressed phagocytic activity of the reticuloendothelial system (RES) as measured by clearance of colloidal carbon. When inoculated i.p., triolein moderately enhanced RES activity of germfree mice, while exerting no significant effect in conventional mice. In both groups of mice, however, protection was found against an i.p. challenge of virus. Cortisone greatly suppressed RES activity and significantly increased susceptibility of germfree and conventional mice to MHV-1. Triolein also was found to protect mice against the combined challenge of cortisone plus virus. However, triolein, whether injected i.p. or i.v., failed to protect against an i.v. challenge of virus. These data support two conclusions: (1) triolein exerted its protective effect at some site other than the macrophages of the liver; (2) protection against MHV-1 infection following triolein treatment was not related to the carbon clearing activity of the RES.