Study on Immunological Examination in Blood with Two Streptococcus suis Serotype 2 Strains Infection in Miniature Swine Model

To investigate the changes of immuneparameter induced by the infection of Streptococcus suis serotype 2 (SS2) in mini-swine model. The pigs were inoculated with 1 times 10⁷ CFU ml^-1/kg of two SS2 strains (ZY05719 and HA9801). Typical clinical symptoms and pathological features were confirmed after infection. Bacterial content in certain organs and changes of white blood cell counts were measured; T cell subsets, T cell proliferative function, cytokines and chemotacticfactors (IL-1, IL-8, TNF-alpha and IFN-gamma) were measured. Phagocytosis of neutrophil was determined by NBT reduction test. Our results showed that SS2 would lead acute, subacute infection and chronic persistent. High bacterial content of 10⁶CFU/ml occured in blood at acute phase, IL-1, IL-8, TNF-alpha and IFN-gamma significantly increased at 12 h after infection. Obvious CD4⁺ cells decreasing while CD8⁺ increasing were observed in dead pigs. Lymphocyte transformation ability was irregular in dead pigs, while transformation index in subacute infected pigs recovered gradually after one week deceasing. WBC counts decreased 1-2 days after infection, then increased and hit the peak on day 5 after infection. The phagocytic ability of neutrophil was impaired in post-infection period. Variation of the total WBC number, neutrophil phagocytic ability and different symptoms of pigs. Our findings suggest that there are differences in pathogenicity between ZY0571 and HA9801. The changes of T cells subsets cytokine secretive capacity were associated with the infection progression of SS2.