PHAGOCYTES Human Immunoglobulin A Receptor (FcaRI, CD89) Function in Transgenic Mice Requires Both FcR g Chain and CR3 (CD11b/CD18)

Even though more immunoglobulin A (IgA) is produced in humans than all other isotypes combined, relatively little is known about receptors that bind the Fc part of IgA. The myeloid IgA receptor, FcaRI (CD89), triggers various effector functions in vitro, but its in vivo role remains unclear. Here, a transgenic mouse model is described in which FcaRI is expressed under its own regulatory sequences. Receptor expression and regulation by cytokines was comparable to the human situation and hFcaRI can trigger phagocytosis and lysis of tumor cells. To analyze the contribution of the FcR g chain or the b2 integrin CR3 (CD11b/CD18) in FcaRI biological function, FcaRI transgenic mice were crossed with either FcR g chain 2/2 or CR3 2/2 mice. In contrast to in vitro data, FcR g chain was essential for surface expression of hFcaRI in vivo. Functional studies in hFcaRI / g2/2mic