Antigen-specific proliferation of porcine CD8 alpha alpha cells to an extracellular bacterial pathogen

A vaccine inducing protective immunity to a spirochaete-induced colitis of pigs predominantly stimulates expansion of CD8(+) cells in vivo and in anti gen-stimulated lymphocyte cultures. CD8(+) cells, however, are rarely consi dered necessary for protection against extracellular bacterial pathogens. I n the present study, pigs recovering from colitis resulting from experiment al infection with Brachyspira (Serpulina) hyodysenteriae had increased perc entages of peripheral blood CD4(-) CD8(+) (alpha alpha -expressing) cells c ompared with non-infected pigs. CD8 alpha alpha (+) cells proliferated in a ntigen-stimulated cultures of peripheral blood mononuclear cells from B. hy odysenteriae-vaccinated pigs. Proliferating CD8 alpha alpha (+) cells consi sted of CD4(-), CD4(+) and gamma delta T-cell receptor-positive cells. CD4( -) CD8 alpha beta (+) cells from vaccinated or infected pigs did not prolif erate upon in vitro antigen stimulation. Of the CD8 alpha alpha cells that had proliferated, flow cytometric analysis indicated that the majority of t he CD4(+) CD8(+) cells were large (i.e. lymphoblasts) whereas the CD4(-) CD 8(+) cells were predominantly small. Addition of monoclonal antibodies (mAb ) specific for either porcine major histocompatibility complex (MHC) class I or class II antigens diminished B. hyodysenteriae-specific proliferative responses whereas addition of mAb to porcine MHC II, but not porcine MHC I, reduced the CD8 alpha alpha response. In vitro depletion of CD4(+) cells b y flow cytometric cell sorting diminished, but did not completely abrogate, the proliferative response of cells from vaccinated pigs to B. hyodysenter iae antigen stimulation. These results suggest that CD8 alpha alpha cells a re involved in recovery and possibly protection from a spirochaete-induced colitis of pigs; yet, this response appears to be partially dependent upon CD4(+) cells.