Human bronchial intraepithelial T cells produce interferon-gamma and stimulate epithelial cells.

Intraepithelial lymphocytes (IELs) can be identified among epithelial cells in systemic mucosal tissues. Although intestinal IELs play a crucial role in mucosal immunity, their bronchial counterparts have not been well studied. The purpose of this study was to determine the immunological functions of human bronchial IELs, which interact directly with epithelial cells, unlike lamina propria lymphocytes (LPLs). We isolated successfully bronchial IELs and LPLs using a magnetic cell separation system from the T cell suspensions extracted from bronchial specimens far from the tumours of resected lungs. Human bronchial IELs showed an apparent type 1 cytokine profile and proliferated more actively in response to CD2 signalling than did bronchial LPLs. CD8(+) IELs were identified as the most significant sources of interferon (IFN)-gamma. Human bronchial epithelial cells constitutively produced the T cell growth factors interleukin (IL)-7 and IL-15, and levels of those factors increased when cells were stimulated by IFN-gamma. Bronchial epithelial cells expressed cell surface proteins CD58 and E-cadherin, possibly enabling adhesion to IELs. In summary, human bronchial IELs have immunological functions distinct from bronchial LPLs and may interact with epithelial cells to maintain mucosal homeostasis.