IMMUNOLOGICAL AND ELECTRON-MICROSCOPIC STUDIES IN PIGS INFECTED WITH YERSINIA-ENTEROCOLITICA-0 3/

The cellular immune response after an experimental oral infection with Yersinia enterocolitica (serotype 0:3, biotype 4, harbouring the viru lence plasmid - pYV) was studied in pigs. A maximal stimulation of the T cell population in the thymus, spleen and peripheral blood was stat ed on the 15th day post infection (p.i.) by the rosette forming cell ( RFC) test. The hemolysins (produced by B cells and detected by the pla que forming cell test PFC) were significantly increased on the 15th da y p.i. among the thymus and spleen lymphocytes and on the 25th day p.i . among the blood lymphocytes. Blood and thymus lymphocytes were activ ated faster by the infectious agent in comparison to the spleen cells. The electronmicroscopic studies revealed an intracellular presence of the bacteria in alveolar macrophages (aMa) and peritoneal macrophages (pMa) as well as in Peyer's patches and tonsils as early as on the 4t h day p.i. Extracellularly located bacteria were observed, too. The re sults have shown that inspite of the activation of T and B cell immune response, this infectious agent persisted in the porcine organism.