Effect of thymopentin on the mortality and immune response after an experimental herpes simplex infection in mice

The effect of thymopentin on the mortality rate of mice treated with lethal doses (LD90) of herpes virus 2 and on the cytotoxic T cell activity after sublethal doses (LD10) of herpes virus was investigated in two series of experiments. Doses of 1, 0.1 or 0.01 ng of thymopentin per g/mouse were administered i.p. in each experiment, either 3 days before, 3 days (66 h) after, or 3 and 6 days after the herpes virus infection. The cumulative mortality rate was evaluated 10 days after the infection. Cytotoxic T cell activity was measured 3, 7 and 14 days after the infection. The 0.1-ng dose of thymopentin reduced the mortality rate to less than 50% (p = 0.0000) if it was administered 3 days before the infection. A single injection of any dose after infection did not reduce the mortality at all, while two injections of 0.1 ng reduced it by about 25% (p = 0.0038). A 1-ng dose showed a mild but significant reduction (p = 0.0313) if it was applied 3 days before the infection. The cytotoxic T cell activity was either not influenced or significantly modified (p < 0.05), i.e. increased or decreased as compared to the control, depending on the dose and timing of thymopentin. A correlation between increased cytotoxic T cell activity and protection against mortality can be demonstrated, while no protection was observed in dose regimens where the cytotoxic T cell activity became reduced. The results are discussed in connection with earlier clinical studies in which the beneficial effect of thymopentin has been demonstrated in frequently relapsing herpes labialis and herpes genitalis patients.