Immune response to haemophilus parahaemolyticus (HP) infection in the pig I. In vitro tests to detect sensitized cells in the blood of infected and vaccinated animals

The in vitro immune response of pigs in herds infected or non-infected with H. parahaemolyticus (HP) was investigated by lymphocyte stimulation and leucocyte migration inhibition tests. The stimulation of pig lymphocytes with HP bacteria has been measured by ³H-thymidine incorporation. The response of the cells seems to be specific, lymphocytes from chronically HP-infected animals showed positive reactions with high frequency, while on the contrary, cells from SPF (specific pathogen free) animals reacted only occasionally to the HP antigens. However, in the leucocyte migration inhibition test the reactions were less specific; the widely occurring H. parasuis bacteria seem to possess antigen(s) which causes cross reactions with HP in this test.Vaccination with HP bacteria induced sensitive lymphocytes in the blood of SPF pigs and an increase of the in vitro lymphocyte reactions in already positive animals.