The binding of staphylococcal protein A by the sera of different animal species.

The capacity of purified immunoglobulin or serum to bind (125I)-labeled staphylococcal protein A (SPA) was measured by means of an immunofiltration assay that facilitated the examination of large numbers of sera and required only a minute quantity of each. Sera from 80 species, including humans, laboratory animals, domestic animals, and a variety of African mammals were examined. A wide interspecies variation in the SPA-binding capacity of serum immunoglobulins was confirmed. Only small variations were observed among individuals within the same species with one notable exception. A greater than 10,000-fold variation in SPA-binding capacity was observed among sera from nine goats. Interspecies differences in serum SPA-binding capacity correlated well with taxonomic differences, and the serum SPA-binding capacity correlated well with taxonomic differences, and the serum SPA-binding capacities of African mammals corresponded closely to those of their more common relatives. The sensitivity of antibody detection by indirect (125I)SPA immunoassay was shown to be determined mostly by the SPA-binding capacity of the serum examined. The titer of antibody to influenza A/Texas/1/77(H3N2) virus in sera from several different species, when measured by (125I)SPA immunofiltration assay, was directly proportional to the SPA-binding capacity of the serum and was not proportional to the hemagglutination inhibition titer. An (125I)SPA immunofiltration assay for antibody to Lassa virus in the serum of Mastomys natalensis (which binds SPA only one-thousandth as well as human serum) was at least as sensitive as the standard fluorescent antibody assay.