Mac-1 (CD11b/CD18) as Accessory Molecule for FcαR (CD89) Binding of IgA

Abstract

IgA, the principal ligand for FcαRI, exists in serum as monomeric IgA and at mucosal sites as secretory IgA (SIgA). SIgA consists of dimeric IgA linked by joining chain and secretory components. Human polymorphonuclear leukocytes (PMN) and mouse PMN transgenic for human FcαRI exhibited spreading and elicited respiratory burst activity upon interaction with either serum or SIgA. However, PMN devoid of the β2 integrin Mac-1 (Mac-1−/−) were unable to bind SIgA, despite expression of FcαRI. Consistent with this, serum IgA stimulated Mac-1−/− PMN oxygen radical production, in contrast to SIgA. Binding studies showed the secretory component, by itself, to interact with Mac-1-expressing PMN, but not with Mac-1−/− PMN. These data demonstrate an essential role for Mac-1 in establishing SIgA-FcαRI interactions.