Reactivity of natural IgM antibodies with sperm head surface proteins. Use of an ELISA to characterize the reaction.

The data and system of analysis presented in this report have defined a subset of natural IgM antibodies in human sera that are reactive with specific members of a fraction of proteins extracted from human sperm heads. An ELISA has been developed in which, by use of a standardized reference serum, the relative values for total IgM and for sperm protein-reactive IgM may be derived for each serum. Those values, determined for 32 adult and 9 neonatal sera, indicate that the sperm protein-reactive IgM antibodies represent a reasonably constant proportion of the total serum IgM titer. Other assay data indicate that the reactivity between the antigenic sperm proteins and IgM antibodies is of high affinity. Although immunotransfers of this study have confirmed an earlier report (Rodman et al., 1985) that the immunoreactive elements of the sperm protein fraction include 7-9 separate bands or doublets, the data suggest that the reactivity is not a composite of multiple heterogeneous reactions but may be that of a few or a specific reaction, possibly involving homologous or cross-reactive antigenic determinants.