Levamisole exacerbates coxsackievirus B3-induced murine myocarditis

Levamisole administration to several strains of adolescent mice at the time of or up to 4 days post-inoculation (p.i.) with a myocarditic variant of coxsackievirus B3 (CVB3m) increased the number of myocarditic lesions above that found in CVB3m-inoculated mice. Virus replication in heart tissues in vivo was not affected by levamisole administration to the mice, nor was production of neutralizing antibody to CVB3m. Lymphocytes from nodes of virus-inoculated mice treated with levamisole at 2 days p.i. exhibited an increased reactivity to phytohemagglutinin on days 6 and 8 p.i., compared with respective responses by nodal T lymphocytes from CVB3m-inoculated mice. Levamisole treatment of CVB3m-inoculated mice also increased the reactivity of splenic and peripheral blood T lymphocytes to phytohemagglutinin on day 8 p.i., but not day 6 p.i., compared with the respective responses by lymphocytes from CVB3m-inoculated mice. The proportion of theta antigen-bearing lymphocytes in the total lymphocyte population in peripheral blood of CVB3m-inoculated mice was not altered by levamisole treatment. However, CVB3m-induced reduction in this subpopulation of lymphocytes in the nodes was restored to control levels by levamisole treatment. Reactivities of cytotoxic T lymphocytes from CVB3m-inoculated mice were increased against both normal and CVB3m-inoculated target cells after levamisole treatment of these mice. The results suggest that levamisole may contribute to CVB3m induction of myocarditis by several mechanisms, such as increasing the blastogenic activity of the phytohemagglutinin-responding subset of T lymphocytes, by possibly altering T-lymphocyte distribution in the body and by nonspecifically increasing reactivities of cytotoxic T lymphocytes.