Previous publications describe preparation of Tacaribe, Junín and Machupo virus antigens and their reciprocal cross-reactions in the complement fixation (CF) test (Mettler 1961, Wiebenga 1964, Johnson 1965). Production of plaques after viral infection of cell cultures (Tauraso 1964) and serum neutralization of plaques by homotypic antiserum (Johnson 1965) were also reported. The following report adds recent observations by CF and plaque neutralization tests and presents results of some challenge experiments in vivo.
The CF test was used to assay immune ascitic fluids (IAF) obtained from mice and hamsters after intraperitoneal (i.p.) inoculation of live Machupo virus and complete Freund's adjuvant according to the schedule indicated in Figure 1. In contrast with previous experience with 21-day-old mice, ascitic fluid was not obtained from hamsters less than 3 months of age. Antibody titers of ascitic fluid samples were determined by CF test techniques previously described (Wiebenga 1964). Sucrose-acetone extracted Junfn virus antigen (Mettler 1963) was used in these tests because it was more potent than chloroform-inactivated Machupo virus antigen and cross-reacted with Machupo virus antibody (Johnson1965).