Histopathology of arthritis induced in rats by active immunization to mycobacterial antigens or by systemic transfer of T lymphocyte lines. A light and electron microscopic study of the articular surface using cationized ferritin.

We analyzed the histopathologic findings of arthritis in 3 rat models: adjuvant arthritis induced by active immunization to Mycobacterium tuberculosis (MT) antigens, arthritis produced by passive transfer of an intrinsically arthritogenic line of anti-MT T lymphocytes, and bystander arthritis produced by intraarticular injection of a foreign antigen, ovalbumin, into rats with T lymphocyte line cells specific for the ovalbumin antigen. The histopathology of the tibiotarsal and knee joints was studied by light microscopy and the articular surface of the cartilage by electron microscopy after labeling with cationized ferritin. The lesions in the 3 models of arthritis were compared. In active adjuvant arthritis, inflammatory lesions and cartilage destruction were found as early as 9 days after immunization, and persisted for as long as 11 months. Similar, but somewhat milder, lesions were found in arthritis produced by transfer of anti-MT T lymphocytes. Inflammatory signs were present at 4 days, when there was no evidence of joint edema. Severe inflammatory lesions were found in arthritis induced by transfer of anti-ovalbumin T lymphocytes that was followed by ovalbumin injection into the knee. Pathologic changes were found to be similar in all 3 models. Thus, the changes could be attributed to the action of T lymphocytes, irrespective of whether the target antigen was intrinsic to the joint.