Expression of newly identified secretory CEACAM1a isoforms in the intestinal epithelium

Abstract Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) regulates intestinal immunological homeostasis. However, precise expression patterns of CEACAM1 isoforms remain poorly understood in the intestinal epithelia. Focusing on the small intestinal epithelium of BALB/c mice, we identified three novel splice variants encoding CEACAM1 a -2, -2C1, and -4C1 by RT-PCR. CEACAM1 a -2, -2C1, and -4C1 demonstrated secretory properties by transfection experiments in vitro . Among them, CEACAM1 a -4C1 was the major secreted isoform in vivo due to the soluble/secreted CEACAM1 a with a frameshift sequence in the C-terminus, specific for CEACAM1 a -2C1 and -4C1. CEACAM1 a -4C1 was capable of binding murine hepatitis virus (MHV) and was detected at approximately 120 kDa in the small intestinal secretions. Neutralizing effects of the soluble CEACAM1 a on MHV infectivity in vitro were demonstrated by using recombinant CEACAM1 a -4C1. Our data suggest an intrinsic mechanism operated by free CEACAM1 for surveillance of pathogens and maintenance of homeostasis in the intestine.