Role of Ia-positive cells in the lymphocyte responses to Yersinia.

Activation of T lymphocytes by an antigen requires joint recognition of the antigen and the class-II HLA determinants on the membrane of the antigen-presenting cells (APC). Patients with reactive arthritis exhibit a depressed lymphocyte transformation response to Yersinia, suggesting a possible immunoregulatory disturbance in these patients. In this study the role of Ia (class-II HLA antigen)-positive APC in the lymphocyte response to a complex antigen, whole Yersinia bacterium, was evaluated. The results demonstrate that Ia-positive cells are necessary for the T-lymphocyte response to Yersinia. The role of APC in the pathogenesis of reactive arthritis is discussed.