Effect of immunosuppression on chronic LCM virus infection of mice.

C3H mice chronically infected with LCM virus were found to be lethally affected by small doses of immunosuppression which caused bone marrow aplasia but had no effect on the amount of virus carried by the mouse. Humoral immune response of SWR/J mice to acute LCM infection was found to be totally suppressed by repeated single doses of 300 R/wk with no alteration in the level of virus carried by the mouse. In contrast, the established anti-LCM humoral immune response encountered in mice chronically infected with LCM virus was not suppressed by the same irradiation procedure. Over half of the chronic LCM carrier SWR/J mice treated with cyclophosphamide for 6 mo had total anti-LCM humoral immunosuppression, but showed no change in the level of virus carried. The glomerulonephritis which occurs in chronic LCM carrier mice was prevented by cyclophosphamide treatment in 90% of the mice. The humoral immune response which occurs in chronic LCM carrier mice appears to play no role in controlling the amount of virus carried by the mouse. Suppression of the LCM immune response by cyclophosphamide does prevent the development of glomerulonephritis in these mice.