Nicotine and TNF alpha, modulators of T cell signaling-effects on T cell development in fetal thymus organ culture

Abstract

T cell development is regulated by signals generated in the interactions between developing thymocytes and the thymic stroma. Using fetal thymus organ culture (FTOC) as a model of T cell development, we investigated the ability of two potent signal modulators to influence this process. These studies show that both nicotine and tumor necrosis factor-alpha have the ability to influence T cell receptor (TCR) signaling and the maturational capacity of treated cultures. FTOC treated with low concentrations of nicotine produced more immature T cells and fewer mature T cells. These expanded populations of cells also expressed CD69, CD95 (FAS) and elevated levels of recombinase activating genes (RAG). This phenotype reflects the fact that these cells have received a positive selection signal, are for apoptosis and are likely attempting secondary TCR rearrangements. Nicotine effects were partially blocked by the nicotinic antagonist, d-tubocurarine. Furthermore, d-tubocurarine alone blocked the development of T cells entirely, suggesting the presence of an endogenous ligand that may engage nicotinic acetylcholine receptors and regulate normal thymopoeisis. These observations underscore the linkage between the nervous and the immune systems, not only in terms of shared resources, but also in terms of direct interactions between these two systems. In another study we used FTOC and an associated in vitro Type 1 diabetes mellitus model to reconcile the role of TNF-alpha in thymopoiesis with its role in diabetes. Our data indicate that thymocytes from NOD FTOC express lower levels of TNF receptors and produce more TNF-alpha compared to non-diabetic C57BL/6 (B6) FTOC. Neutralization of endogenous TNF-alpha in NOD FTOC with a soluble TNF receptor (sTNF R1) rescued insulin production in our in vitro diabetes model. NOD FTOC treated with TNF-alpha produced greater numbers of mature T cells and a higher percentage of cells expressing CD95L (Fas ligand). Treatment with sTNF R1 had the opposite effect. TNF-alpha's known ability to attenuate TCR signaling coupled with these observations suggest that its overproduction in these animals may be driving T cells to maturity, altering the process of negative selection and ultimately enhancing the survival of potentially diabetogenic T cells resulting in disease susceptibility in these animals.