The Immunomodulatory Properties of Rat Lacrimal Acinar Cells the Role of TGF–ß

Abstract

Abstract: : Purpose: In previous studies, our group demonstrated that rabbit lymphocytes could be activated ex vivo against normal isolated lacrimal gland acinar cells. The goal of this work was to establish the corresponding ex vivo model in rats. Methods: Proliferation of spleen cells (SPC), spleen lymphocytes (SPL), and peripheral blood lymphocytes (PBL) in ex vivo mixed cell reactions (MCRs) with AC was assessed from [³H]–thymidine incorporation or flow cytometric analysis of carboxyfluorescein diacetate label dilution. TGF–ß was detected by Western Blot. Results: SPC and SPL from male Lewis rats proliferated in primary culture, presumably in response to autoantigens presented by dendritic cells (DC), the presence of which could be demonstrated. AC from Lewis rats inhibited lymphocyte proliferation, even when separated by microporous culture inserts. Soluble factors from rat AC also suppressed rabbit AC–SPC and AC–PBL autologous MCRs. Rabbit SPC and PBL from AC MCRs that had been modulated by rat AC soluble factors suppressed fresh AC–SPC and AC–PBL MCRs. Rat AC expressed membrane bound TGF–ß and secreted soluble TGF–ß. Antibody to TGF–ß (Ab–TGF–ß) completely abrogated rat AC inhibition of rabbit AC–PBL MCRs, but recombinant TGF–ß did not mimic this action. Ab–TGF–ß had little effect on rat AC inhibition of rabbit AC–SPC MCRs, but recombinant TGF–ß mimicked the effect of rat AC. Conclusions: Rat AC secrete TGF–ß and other paracrine mediators that educate rat and rabbit lymphocytes to become regulatory cells. Rat AC create a tolerogenic environment that modulates lymphocyte responses to autoantigens presented both by AC and by APC. TGF–ß is necessary, but not sufficient, for prevention of autoimmune PBL activation by AC. Other AC factors inhibit autoimmune SPC activation by DC, but these can be replaced by high concentrations of TGF–ß. These phenomena may comprise an immune deviation that enforces a robust tolerance to autoantigens in the rat lacrimal gland.

Keywords: lacrimal gland • cornea: tears/tear film/dry eye • immune tolerance/privilege