A heterophile carbohydrate moiety common to mammalian IgM and erythrocytes detected by chicken IgM antibody.

Sequential treatment of chicken lymphocytes with normal sheep serum (NSS), chicken antiserum against sheep erythrocytes (SE) and formaldehyde results in rosette formation with SE. The identity of reactive components and the mechanism of rosette formation has been elucidated. The binding activity of NSS to chicken lymphocytes was ascribed to "natural" IgM anti-species antibodies. Subsequently, chicken IgM anti-SE antibody reacted with sheep IgM bound to the lymphocyte surface, and, following formaldehyde fixation, rosettes were formed by the addition of SE. The reaction of chicken anti-SE antibody was competitively inhibited with a hog blood group substance suggesting that it had binding specificity for a carbohydrate moiety which is shared by sheep IgM and SE. This specificity represented only a fraction of the bulk of chicken IgM anti-SE antibodies and was not manifested by antibodies of the IgG class. The analysis by the above-described "sandwich rosette assay" was extended to chicken antisera against horse, rat and mouse red cells and to normal sera from these species. Cross-matching of chicken antisera, with the normal sera and red cells from the tested species revealed a distinct pattern of cross-reactivities. These results imply that the saccharide epitope which is shared by IgM and red cells has a wide distribution between various mammalian species and may be classified as a new system of heterophile antigens.