IL-7, a cytokine produced by thymic epithelium, was shown to induce adhesion of murine thymocytes to gelatin-coated membranes. A major binding component of gelatin was identified as fibronectin. IL-7-induced adhesion was observed for all of the major thymocyte subsets, including double-negative, double-positive, and single-positive cells, and specific IL-7R were verified on each subset. Fibronectin binding was mediated via alpha4beta1 integrin (VLA-4), which is expressed at high levels on thymocytes. VLA-4 surface expression was not increased following IL-7 treatment, but was shown to undergo rapid tyrosine phosphorylation on the beta1 subunit. This tyrosine phosphorylation was blocked by genistein, which also blocked IL-7-induced adhesion. IL-7 was detected on the extracellular matrix of the thymus, suggesting that it could promote matrix association through an integrin pathway.
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Kitazawa et al. (1997) studied this question.