Changes in rat leukocyte populations in peripheral blood, spleen, lymph nodes, and synovia during Erysipelas bacteria-induced polyarthritis.

Kinetics of leukocyte subsets were followed for several weeks in rats suffering from polyarthritis induced by experimental infection with erysipelas bacteria (Erysipelothrix rhusiopathiae, serovar 2, strain T28). A marked leukocytosis was found in peripheral blood, and, with some delay, in the synovia and draining lymph nodes of affected joints. In the lymphoid organs tested considerable blast formation of lymphoid cells with a paucity of polymorphonuclear granulocytes was found, while the latter represented the majority of leukocytes in acutely inflamed joints. Cells isolated from spleen showed only moderate and transient alterations in proportions of subpopulations during the first week after inoculation of erysipelas bacteria. In contrast, cells isolated from synovia of inflamed joints and draining lymph nodes displayed more intense and longer lasting alterations: In arthritic animals, the proportion of MHC class II-positive lymphocytes generally increased and remained elevated at least during the first three weeks of the disease. Spontaneous release of IL-2 from cells isolated up to 20 days post induction of the arthritis indicated a considerable activation of lymphocytes in vivo. Interestingly, with exception of synovia, the relative amount of T-lymphocytes including their major CD4+ and minor CD8+ subsets showed little alteration during the course of the disease. Much more pronounced were the rapidly and the extent the membrane Ig-positive B-lymphocytes increased in the synovia as well as in the lymph nodes. Thus, B-lymphocytes may be of particular relevance for elucidating pathomechanisms of erysipelas polyarthritis.