1996;215:282C302. cell sorting diminished, but did not completely abrogate, the proliferative response of cells from vaccinated pigs to antigen activation. These results suggest that CD8 cells are involved Toll-like receptor modulator in recovery and possibly protection from a spirochaete-induced colitis of pigs; yet, this response appears to be partially dependent upon CD4+ cells. Introduction Toll-like receptor modulator Cytotoxic T cells of rodents and humans express CD8 predominantly as an heterodimer.1,2 Lymphocytes expressing CD8 homodimers also exist in low figures on subpopulations of natural killer cells, intraepithelial lymphocytes, activated T cells and T cells of these species.3C5 Pigs, however, are different in comparison to rodents and humans in several aspects of their T-cell biology. They have expanded pools of circulating CD4+ CD8+ cells, CD4C CD8+ cells and T cell receptor (TCR)+ cells.6C10 Porcine CD4+ CD8+ cells are considered mature memory/effector lymphocytes with exhibited reactivity to alloantigens, superantigens, or viral antigens.10,11 Porcine CD4C CD8+ cells have only recently been described and are defined by their low intensity of staining with the monoclonal antibody (mAb) 76-2-11 which is specific for the CD8 chain and for their lack of reactivity with both mAb PG164A, which is specific for the CD8 chain, and mAbs specific for porcine CD4 (ref. 12 and Zuckermann, unpublished observations). CD8+ cells are further subdivided into TCR+, TCR+, or natural killer cells.9,13 By circulation cytometry, porcine CD8-expressing cells SF1 are characterized as CD8lo whereas CD8-expressing cells are characterized as CD8hi cells.9 The CD8 molecule functions as a co-receptor for TCR-mediated activation via association with the protein tyrosine kinase p56lck.14,15 Although CD8 chains are sufficient for cellular activation, expression of the chain results in more efficient Toll-like receptor modulator co-receptor activity.16 Murine CD8 heterodimer-expressing cells are fundamental for protection to infection.17C19 Murine CD8 homodimer-expressing Toll-like receptor modulator cells have been detected within lesions of 2-microglobulin-deficient mice.20 These CD8+ cells are MHC class I-independent, predominantly TCR+, and presumed to be extrathymically derived. Although it is usually clear that CD8 cells are key in the immune response to certain intracellular bacterial pathogens, no obvious roles have been defined for CD8+ cells to extracellular bacterial infections. is an extracellular mucosal pathogen of pigs that induces a mucohaemorrhagic colitis. It is non-invasive, inducing diarrhoeal disease without systemic spread of the spirochaete. Vaccination with a protease-digested bacterin protects pigs from disease and induces a cellular immune response as measured by antigen-specific blastogenesis, interferon- (IFN-) production and a delayed-type hypersensitivity reaction.21 Recently, it was determined that this cells from vaccinated pigs predominantly responding in the recall proliferative response to antigens are CD8+ and/or TCR+ cells.22 The present findings demonstrate a correlation between the induction of a CD8 proliferative response and recovery or protection from a spirochaete-induced colitis of pigs. Materials and methods Pigs and challengeFour- to five-week-old cross-bred pigs in a breeding herd managed at the College of Veterinary Medicine, Iowa State University or college, Ames, IA were utilized for the study. Pigs were monitored daily for any indicators of illness. Throughout the experiments, no clinical indicators of respiratory or enteric disease were detected other than diarrhoea associated with challenge. challenge inoculum was prepared as previously explained.23 Briefly, strain B204 was grown under anaerobic conditions in trypticase soy broth (Becton Dickinson and Co.; Cockeysville, MD) supplemented with 5% horse serum (Hyclone; Logan, UT), 05% yeast extract (Difco; Detroit, MI) and VPI salts (Virginia Polytechnic Institute Anaerobic Laboratories; Blacksburg, VA, USA). All cultures used for contamination studies were 90% motile and had been passed fewer than 25 occasions. Challenge inoculum consisted of two doses of 1010 strain B204 organisms.