Differential Contribution of Fas- and Perforin-Mediated Mechanisms to the Cell-Mediated Cytotoxic Activity of Naive and In Vivo-Primed Intestinal Intraepithelial Lymphocytes

Abstract

Intestinal intraepithelial lymphocytes (IELs) are known to exert strong constitutive cytotoxic activity. In the present study we compared the Ag-specific cytotoxic activity and the effector mechanisms involved in non-Ag-primed, naive and in in vivo-primed IELs and splenic CD8 T cells. Ex vivo isolated naive CD8αα TCRαβ IELs, CD8αβ IELs, and splenocytes from lymphocytic choriomeningitis virus (LCMV)-specific TCR transgenic mice exert Ag-specific cytotoxic activity in a long-term, but not in a short-term, cytotoxicity assay. This cytotoxic activity is mainly Fas-Fas ligand mediated and is significantly reduced in the presence of 20 μg/ml Fas-Fcγ1 fusion protein. Both CD8αβ IELs and CD8αβ splenocytes isolated from LCMV-infected C57BL/6 mice exert potent perforin-dependent cell-mediated cytotoxicity. CD8αα TCRαβ IELs from LCMV-infected animals, however, show only minimal Ag-specific cytotoxicity. The potent cytotoxic activity of in vivo activated CD8αβ IELs is not affected by the addition of Fas-Fcγ1. Nevertheless CD8αβ IELs from LCMV-infected perforin-deficient mice exert Ag-specific cytotoxicity in a short-term cytotoxicity assay, and this cytotoxicity is almost completely blocked by the addition of Fas-Fcγ1. These results demonstrate that naive CD8αβ IELs exert Ag-specific, Fas-Fas ligand-mediated, constitutive cytotoxic activity in a long-term cytotoxicity assay, whereas primed CD8αβ IELs primarily use the perforin-dependent exocytosis pathway to exert their potent cytotoxic activity. Furthermore, these results clearly illustrate the requirement for Ag-specific determination of IEL-mediated cytotoxicity, because the elevated, but variable, frequencies of memory-type T cells in this compartment may lead to ambiguous results when polyclonal activation or redirected assays are used.

Phenotyping, functional characterization, and developmental changes in canine intestinal intraepithelial lymphocytes

“…Type a mucosal T cells have much in common with peripheral CD4 + or CD8ab + cells, but also show some gut-specific regulatory functions. Thus, CD8ab + TCRab IEL may exert some cytolytic functions [4], whereas resident (non-infiltrating) CD4 + TCRab cells often show a regulatory phenotype [3]. Type b TCRcd cells likely play a dual role in the regulation of protective immune responses and the regulation of epithelial layer integrity via the release of keratinocyte growth factor [1].…”

Selective upregulation of immune regulatory and effector cytokine synthesis by intestinal intraepithelial lymphocytes following CD43 costimulation

“…For example, the majority of CD8+ IELs express CD69, a marker of recently-activated lymphocytes [1]. Moreover, without in vitro activation, IELs are constitutively cytolytic [2][3][4][5], suggesting that they are not classical resting T cells. However, IELs have limited capacity for proliferation and they do not spontaneously produce cytokines [6,7], both of which are properties that belie the likelihood that they are fully-activated T cells.…”

Immunopathology of giardiasis: the role of lymphocytes in intestinal epithelial injury and malfunction

“…Immunostaining of Giardia-infected human intestinal tissues has demonstrated that these specimen's intraepithelial lymphocytes, which are mostly CD8 + T cells, are positive for T-cell restricted intracellular antigen (TIA)-1, but negative of Granzyme B, implying that these CD8 + T cells are resting cytotoxic cells (Oberhuber et al 1996). Furthermore, CD8 + IEL isolated from TCR transgenic mice exhibit antigen-specific perforin-and FasL-mediated cytotoxic activity toward intestinal epithelial cells and T cells (Corazza et al 2000, Melgar et al 2002. Potent FasLdependent cytolytic activity of CD8 + IEL toward enterocytes was also reported in graft-versus-host disease, which shares a number of the pathophysiological features of giardiasis (Corazza et al 2000).…”

“…Furthermore, CD8 + IEL isolated from TCR transgenic mice exhibit antigen-specific perforin-and FasL-mediated cytotoxic activity toward intestinal epithelial cells and T cells (Corazza et al 2000, Melgar et al 2002. Potent FasLdependent cytolytic activity of CD8 + IEL toward enterocytes was also reported in graft-versus-host disease, which shares a number of the pathophysiological features of giardiasis (Corazza et al 2000). In graft versus host disease-associated intestinal inflammation, or upon intestinal bacterial infection, IEL express a high level of the integrin α Xβ 2 (Huleatt et al 1995).…”