Effect of immunosuppression on recurrent herpes simplex in mice

Mice latently infected with herpes simplex virus were treated with immunosuppressive drugs either alone or combined with stimuli to the skin. Treatment with cyclophosphamide reduced spleen weights and severely depressed lymphocyte levels, but had no effect on healing after cellophane tape stripping (CTS) and did not affect the cutaneous hypersensitivity response after injection of inactivated herpes simplex virus. The drug, either used alone or combined with CTS, failed to increase the incidence of recurrent clinical disease, but increased the incidence of virus isolation after CTS. Prednisolone and azathioprine used together also reduced spleen weights and circulating lymphocyte levels. They slightly delayed healing after CTS, but had no effect on cutaneous hypersensitivity to herpes simplex virus. The treatment, either used alone or combined with CTS, slightly increased the incidence of recurrent clinical disease but did not increase the incidence of virus isolation after CTS. Treatment with antithymocyte serum severely depressed the levels of circulating lymphocytes and delayed the regression of HeLa cell tumors in mice. Used alone, the treatment slightly increased the incidence of recurrent clinical disease, but it failed to increase the incidence of recurrences after CTS. It increased the duration of recurrent herpetic lesions, although in uninfected mice healing after CTS was not affected. Silica altered the clinical course of primary infection with herpes simplex virus and increased the incidence of latency in the ganglia. It also delayed healing after CTS in uninfected mice, so it was not tested when recurrent herpes after CTS was assessed clinically. Treatment with silica alone did not increase the incidence of recurrent clinical disease or the incidence of virus isolation after CTS. The results demonstrate that potent immunosuppressive drugs are much less effective than simple cutaneous manipulation in inducing recurrent lesions, and thus argue strongly for the importance of local factors in the pathogenesis of disease.