Immunohistochemical study of lymphoid tissues in adjuvant arthritis (AA) by image analysis; relationship with synovial lesions

The aim of this study was to examine leucocyte populations in lymphoid orga ns during AA and to ascertain the relationship with lesions in synovial joi nts. Popliteal lymph nodes, spleen and knee synovial membranes were removed from both healthy and AA rats at intervals of 3-4 days over a 3-week perio d. Cryostat sections were stained with MoAbs directed against lymphocyte an d macrophage subpopulations, and studied by image analysis. Throughout the arthritic period, high numbers of ED1(+) and ED3(+) macrophages were seen i n both lymphoid compartments and intercellular adhesion molecule-1 (ICAM-1) expression also increased in some zones of lymph nodes and spleen. The per centages of CD4(+) and CD8(+) cells rose in the splenic zones studied but f ell in the lymph node cortex. Very few natural killer (NK) cells were found in lymphoid tissues, but the number rose after AA induction. In synovia fr om AA rats, ED2(+) macrophages proliferated but alpha/beta T cell infiltrat ion was only occasionally observed, accompanied by ED1(+) cells and ICAM-1 expression. In conclusion, synovitis developing after AA induction seems to be caused directly by macrophages and indirectly by lymphocytes placed bot h in popliteal lymph nodes and spleen.