Function of αβ TCR+ intestinal intraepithelial lymphocytes: Th1-and Th2-type cytokine production by CD4+ CD8− and CD4+ CD8+ T cells for helper activity

Abstract

The immunobiological function of lymphocytes within the epithelium (IELs) of the small intestine is incompletely understood; however, it has been shown that intestinal IEL T cells exhibit cytotoxiclty, produce cytokines, and perform some regulatory roles. In this study, we have focused on CD4⁺, αβ TCR⁺ IELs, which comprise∼15—20%; of the total population, for helper functions. We have assessed the profile of type 1 or type 2 T_h cell cytokines produced in αβ TCR bearing CD4⁺CD8⁻ and CD4⁺CD8⁺ (double positive, DP) intestinal IELs by cytokine-specific ELISPOT and by reverse transcription-polymerase chain reaction. Help for B cells taken from Peyer's patches (PP) allowed us to assess IEL function for mucosal antibody responses. Freshly isolated CD4⁺CD8⁻ IEL T cells contain T_h2-type cells, e.g. high numbers of IL-5 secreting (spot forming) cells (SFC) followed by IL-4 and IL-6, while DP T cells have IL-5 and IL-6 producing cells, but not IL-4. In addition to T_h2-like cytokine producing T cells, both CD4+ T cell subsets contain IFN-γ, secreting T_h1-type cells but neither subset synthesizes IL-2. Stimulation of CD4⁺CD8⁻ and DP T cells with solid phase mAb anti-CD3 resulted in production of IL-2 in addition to IFN-γ, IL-5, and IL-6, and this treatment stimulated DP T cells to produce IL-4. When freshly isolated intestinal IEL T cells were separated into CD4⁺ and CD4⁻ cells, and co-cultured with PP B cells, the former subset supported Ig synthesis including IgA responses, while the later fraction did not. Further, purified αβ TCR⁺, CD4⁺CD8⁻ T cells and DP T cells from IELs when added to PP B cell cultures induced increased numbers of Ig secreting cells. However, CD4⁻CD8⁺ T cells which produced a similar profile of cytokines did not provide helper function for B cells. Our study has shown that αβ TCR⁺ T cells from intestinal IELs exhibit T_h1- and T_h2-type cell functions. Of significant Interest was the finding that DP T cells exhibit cytokine synthesis and helper function in the epithelium of the gastrointestinal tract in addition to CD3⁺ IELs expressing a classical helper phenotype (CD4⁺CD8⁻).