Polarized Expression of CD74 by Gastric Epithelial Cells

Carlos A. Barrera ¹, Ellen J. Beswick ¹, Johanna C. Sierra ¹, David Bland ¹, Rosario Espejo ¹, Randy Mifflin ¹, Patrick Adegboyega ¹, Sheila E. Crowe ¹, Peter B. Ernst ¹ and Victor E. Reyes ^1*

¹ Departments of Pediatrics (EJB,JCS,RE,VER) and Microbiology and Immunology (DB,VER), Internal Medicine (RM), and Pathology (CAB,PA), University of Texas Medical Branch, Galveston, Texas, and Digestive Health Center, Department of Internal Medicine, University of Virginia, Charlottesville, Virginia (SEC,PBE)

^* To whom correspondence should be addressed. E-mail: vreyes{at}utmb.edu.

Submitted on October 15, 2004
Accepted on 4 May 2005

	Abstract

CD74 is known as the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) that regulates the cell biology and functions of MHC class II molecules. Class II MHC and Ii expression was believed to be restricted to classical antigen-presenting cells (APC); however, during inflammation other cell types, including mucosal epithelial cells have also been reported to express class II MHC molecules. Given the importance of Ii in the biology of class II MHC, we sought to examine the expression of Ii by gastric epithelial cells (GEC) to determine whether class II MHC molecules in these nonconventional APC cells were under the control of Ii and to further support the role that these cells may play in local immune and inflammatory responses during Helicobacter pylori infection. Thus, we examined the expression of Ii on GEC from human biopsy samples, and then confirmed this observation using independent methods on several GEC lines. The mRNA for Ii was detected by RT-PCR, and the various protein isoforms were also detected. Interestingly, these cells have a high level expression of surface Ii, which is polarized to the apical surface. These studies are the first to demonstrate the constitutive expression of Ii by human GEC.

Key Words: antigen presentation, CD74, invariant chain, mucosal immunity.

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