Action of antithymocyte serum on Junin virus infection in rats.

Two-day-old rats resistant to intracerebral (i.c.) infection with XJ strain of Junin virus (JV), were rendered sensitive to JV by treatment with antithymocyte serum (ATS). The mortality reached 80%, the virus titres in brain were higher and the serum neutralizing antibodies dropped but brain lesions were absent throughout. The same host was susceptible to XJCl3 strain infection, which induced lethal encephalitis manifested by severe necrotic foci in cerebellum. ATS treatment conferred significant protection against this strain; the mortality was 63%, viral titres in brain remained unchanged but the lesions were mild as compared with non-treated animals. It seems likely that the XJ strain allowed the 2-day-old rat to develop serum antibodies against JV, while the XJCl3 strain unleashed an immunopathologic response.