Leucocyte function-associated antigen-1 (LFA-1) is known to be involved in immune reactions leading to allograft rejection. The role of deactivating LFA-1 in this context has not been investigated yet, although it is accepted that regulating LFA-1 activity is essential for T-cell function. Expressing LFA-1 locked in an active state in mice (LFA-1(d/d)) allowed us to investigate the in vivo function of LFA-1 deactivation for allograft rejection in a model of heterotopic cardiac transplantation. We provide in vivo evidence that regulating LFA-1 activity from an active to an inactive state controls antigen-specific priming and proliferation of T cells in response to allogeneic stimuli. Consequently, defective LFA-1 deactivation significantly prolonged cardiac allograft survival. Furthermore, reduced numbers of alloantigen-specific T cells and non-allo-specific innate immune cells within allografts of LFA-1(d/d) recipients indicate that expression of active LFA-1 impairs inflammatory responses involving all major leucocyte subpopulations. Taken together, our in vivo data suggest that LFA-1 deactivation is important for the formation of inflammatory lesions and rejection of cardiac allografts. Thus, the dynamic regulation of LFA-1 activity, rather than the mere presence of LFA-1, appears to contribute to the control of immune reactions inducing allogeneic transplant rejection.