Comparative responses of porcine TCRαβCD4 and TCRγδ lymphocytes to a proteinase-digested preparation of Brachyspira hyodysenteriae

Hontecillas, R., J. Bassaganya-Riera, and M.J. Wannemuehler (2001) Comparative responses of porcine TCRabCD4 and TCRγδ lymphocytes to a proteinase-digested preparation of Brachyspira hyodysenteriae. Proceedings of the 82^nd Annual Meeting of the Conference of Research Workers in Animal Diseases; Nov 11-13; St. Louis, MO; (Abstract #142).

Cell-mediated immune responses to bacterial antigens in porcine are regulated by a phenotypically-heterogenous pool of T cells. Both TCRαβCD4 and TCRγδ cells represent an important portion of peripheral blood T lymphocytes. In pigs, expression of the CD8 molecule as an alpha/alpha homodimer following activation is a common phenotypic feature of these two cell subsets. A proteinase-digested (PD) bacterin of the gram-negative spirochete B. hyodysenteriae was previously described to increase the percentage of CD8αα-positive peripheral blood mononuclear cells (PBMC). In the present study, the same antigenic preparation was utilized to assess functional differences between TCRαβCD4 and TCRγδ cells. Pigs inoculated on days 0, 10, and 20 of the experiment with either adjuvant alone (n=8) or the PD bacterin (n=8) were used as source of PBMC for phenotypic evaluation and ex-vivo proliferation assays. Blood samples were collected on days 0, 14, 21, 28 and 35. Flow cytometric evaluation of PBMC revealed that while the first immunization enhanced numbers of TCRαβCD4 and TCRαβCD4CD8αα PBMC, a transient increase of TCRγδCD8αα lymphocytes was detected only after the third immunization. On day 26, isolated PBMC were stained with a fluorescent dye and cultured for 5 days with or without antigen to evaluate proliferative responses of the lymphocyte subsets most affected by immunization. TCRαβCD4 and TCRαβCD4CD8αα recovered from immunized pigs proliferated in response to the antigen preparation but not when cultured with media alone. Conversely, significant proliferative responses of TCRγδCD8αα lymphocytes were detected in porcine PBMC irrespective of the culture conditions (i.e., media alone or antigen). In addition, TCRαβCD4 and TCRγδ cells expressing the CD8αα molecule had a greater proliferative response than CD8αα-negative cells. Thus, while TCRαβCD4 and TCRαβCD4CD8αα activation appeared to be antigen-dependent, the response of TCRγδCD8αα lymphocytes did not depend on the presence of a specific antigen.