Calcineurin deficiency decreases inflammatory lesions in transforming growth factor β1-deficient mice

Transforming growth factor (TGF) β1) is an immunoregulatory cytokine involved in self-tolerance and lymphocyte homeostasis. Tgfb1 knock-out (KO) mice develop severe multi-focal autoimmune inflammatory lesions due to [Ca ²⁺]i deregulation in T cells, and die within 3 weeks after birth. Because the calcineurin inhibitor FK506 inhibits the hyperresponsiveness of Tgfb1^-/- thymocytes, and because calcineurin Aβ (CNAβ)-deficient mice do not reject allogenic tumours, we have generated Tgfb1^-/-Cnab^-/- mice to address whether CNAβ deficiency prevents T cell activation and inflammation in Tgfb1^-/- mice. Here we show that in Tgfb1^-/-Cnab^-/- mice inflammation is reduced significantly relative to that in Tgfb1^-/- mice. However, both CD4⁺ and CD8⁺ T cells in double knock-out (DKO) mice are activated, as revealed by up-regulation of CD11a lymphocyte function-associated antigen-1 (LFA-1), CD44 and CD69 and down-regulation of CD62L. These data suggest that deficiency of CNAβ decreases inflammatory lesions but does not prevent activation of autoreactive T cells. Also Tgfb1^-/- T cells can undergo activation in the absence of CNAβ, probably by using the other isoform of calcineurin (CNAα) in a compensatory manner. CNAβ-deficient T cells undergo spontaneous activation in vivo and are activated upon anti-T cell receptor stimulation in vitro. Understanding the role of calcineurin in T cell regulation should open up new therapeutic opportunities for inflammation and cancer.