Differentiation of variola, monkeypox, and vaccinia antisera by radioimmunoassay.

Poxvirus antisera adsorbed with "homologous" and "heterologous" poxvirus-infected chorioallantoic membranes (CAM) were differentiated by solid-phase radioimmunoassay (RIA). Mixtures of the antiserum dilutions and infected CAM were added directly (without centrifugation) to poxvirus-infected CAM antigens affixed to wells of microtitration plates. The affixed antigens combined with unadsorbed antibodies, and the cross-reactive antigen-antibody complexes were removed by washing. The results showed that adsorption of an antiserum with variola-, vaccinia-, or uninfected-CAM antigen and subsequent reaction of each in RIA with monkeypox- and uninfected-CAM antigens allowed the identification of antivariola, antivaccinia, or antimonkeypox sera.