Cloning and characterization of equine CD89 and identification of the CD89 gene in chimpanzees and rhesus macaques.

Immunoglobulin A (IgA) is the major antibody class present in external secretions of mammals. At the vulnerable mucosal surfaces, IgA provides a crucial first-line defence by neutralizing pathogens. Primates also have a substantial level of IgA in serum and although not well understood, the biological role of this IgA depends, at least partly, on its ability to interact with specific receptors (FcalphaRs) on the surface of leucocytes. The human FcalphaR, CD89, was the first IgA Fc receptor to be identified and binding of IgA-coated particles to CD89 triggers numerous cellular effector functions, including phagocytosis, antibody-dependent cellular cytotoxicity, and release of inflammatory mediators, all of which may play an important role in both systemic and mucosal immunity. For many years humans were the only species known to express CD89, however, it has recently been cloned from cows and rats. Here, we describe the identification of the CD89 gene in three additional species: horses, chimpanzees, and Rhesus macaques. Equine CD89 was identified at the cDNA level, whereas the chimpanzee and Rhesus macaque genes were identified from the available draft genomic sequence. Interestingly, when compared with humans and other primates, horses, cows and rats have a relatively low concentration of serum IgA, so the role of CD89 in these species is of particular interest. The identification and characterization of CD89 in different species will contribute to a greater understanding of the biological role of IgA and CD89 in mucosal and systemic immunity throughout evolution.