Fc alpha/mu R, an Fc receptor for both IgA and IgM, is close to pIgR in gene location and has an Ig-like domain homologous to pIgR. In this study, we generated monoclonal antibodies and determined Fc alpha/mu R and pIgR distributions in human intestinal tissues. Immunohistochernistry analysis showed that, unlike pIgR, which was expressed on epithelial cells of intestinal tissues, Fc alpha/mu R was expressed mainly in the intestinal lamina propria and germinal centers of some lymphoid follicles. Double label immunohistochemistry analysis showed that Fc alpha/mu R was expressed on intestinal macrophages and plasma cells. Fc alpha/mu R was also expressed in Paneth cells. Similar expression patterns for Fc alpha/mu R were observed in the small intestine, appendix, colon and rectum. These results indicate for the first time that Fc alpha/mu R protein is expressed by human intestinal tissues. The different tissue distribution patterns indicate that Fc alpha/mu R and pIgR have different roles in intestinal immunity. (C) 2009 Elsevier Inc. All rights reserved.