Binds to the Fc region of immunoglobulins alpha. Mediates several functions including cytokine production. Associates with the Fc epsilon RI gamma 2 receptor inducing tyrosine phosphorylation of gamma 2. (Microbial infection) Interacts with Staphylococcus aureus protein SSL11. Additional isoforms seem to exist. Isoform A.1, isoform A.2 and isoform A.3 are differentially expressed between blood and mucosal myeloid cells. Isoform A.1, isoform A.2 and isoform A.3 are expressed in monocytes. Isoform A.1 and isoform A.2 are expressed in alveolar macrophages; however only one isoform is expressed at alveolar macrophages surfaces. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.