Review: Fibronectin Receptor Defects in NOD Mouse Leucocytes: Possible Consequences for Type 1 Diabetes

Integrins of the very late antigen (VLA) family mediate leucocyte traffic to lymphoid organs under physiological conditions and in chronic inflammatory situations such as autoimmunity. Accordingly, the current thinking is of a positive correlation between VLA expression and capability of the generation of autoimmunity. Herein we discuss recent findings on the defective expression of integrin-type fibronectin receptors alpha 4 beta 1 (VLA-4) and alpha 5 beta 1 (VLA-5) in the non-obese diabetic (NOD) mouse, a murine model of autoimmune insulin-dependent diabetes mellitus. As compared with normal animals, NOD thymocytes (including the CD4 super(+)CD25 super(+) regulatory T cells) exhibit a decrease in the membrane expression of alpha 5 beta 1, resulting in a functional impairment of fibronectin-mediated interactions, including cell migration. Interestingly, thymocytes that are trapped within the giant perivascular spaces seen in NOD thymus are consistently alpha 5 beta 1 negative, suggesting that the progressive arrest of mature cells can be related to the alpha 5 beta 1 defect. Peripheral T cells also exhibit decreased alpha 5 beta 1 membrane expression and impaired fibronectin-driven migration. Additionally, we observed a defect in alpha 4 beta 1 fibronectin receptor expression in NOD macrophages. Peritoneal, bone marrow-derived-precursor, as well as thymic macrophages of NOD mice showed an impaired upregulation of alpha 4-integrin chain expression, dependent on the level of macrophage maturation. Overall these data lead to the notion that NOD leucocytes bear distinct fibronectin receptor-mediated cell migration defects, which may be involved in the pathogenesis and/or pathophysiology of the autoimmune events seen in NOD mice. Further studies will be helpful to define whether or not this concept can be applied for other autoimmune diseases.