Tight junction protein expression by γδ intraepithelial lymphocytes (IELs) regulates interactions between lymphocytes and epithelial cells

Abstract

Intraepithelial lymphocytes (IEL) are found in the lateral intercellular space. IELs expressing the γδ T‐cell receptor (γδ IELs) promote to mucosal homeostasis, but their interactions with enterocytes have not been clearly defined. To define these interactions in vivo, mice expressing GFP γδ T cells and mRFP‐ZO‐1 within enterocytes were studied by video microscopy and showed that jejunal γδ IEL trafficking is highly dynamic. After crossing the basement membrane, γδ IELs migrate into villous epithelium, approach the tight junction, and exit; all within minutes. Immunofluorescence microscopy of mouse small intestinal γδ IELs, either in situ or after isolation, demonstrated ZO‐1 and occludin expression at bright cell surface punctae, suggesting a role for these proteins in IEL migration. To model this in vitro, murine IELs were applied to the underside of filter‐grown Caco‐2 monolayers. γδ IELs migrated through the filter and across an artificial basement membrane to settle, transiently, just beneath the tight junction. Interestingly, occludin accumulated at γδ IEL‐Caco‐2 contacts. Although epithelial occludin was recruited to sites of occludin knockout γδ IELs‐Caco‐2 contacts, occludin knockout γδ IELs migrated 4‐fold less efficiently than wild type γδ IELs. Thus, γδ IEL trafficking is highly dynamic, both in vitro and in vivo, and depends, in part, on occludin expressed by γδ IELs.