title: CD8-deficient mice exhibit augmented mucosal immune responses and intact adjuvant effects to cholera toxin.
abstract: We used normal, CD4 and CD8 gene-targeted mice to investigate the role of CD4+ and CD8+ T cells in the regulation of gut mucosal immune responses following oral immunizations with cholera toxin (CT) adjuvant. Phenotypic analysis of mucosa-associated tissues revealed normal CD3+ T-cell frequencies in CD4-/- and CD8-/- mice such that in CD4-/- mice the CD8+ and double-negative (DN) T cells were increased. In CD8-/- mice the CD4+ T cells were increased, with the exception that in the intraepithelial compartment the CD3+ T cells were predominantly DN gamma delta T-cell receptor (TCR)+ T cells. All mice, normal and deficient, failed to respond to oral immunization with the antigen, keyhole limpet haemocyanin (KLH), alone. In the presence of CT adjuvant, however, CD8-/- mice consistently exhibited three- to fivefold stronger gut mucosal responses compared to normal C57B1/6 mice. By contrast, no difference was observed for systemic responses between CD8-/- and normal mice. Thus the up-regulation selectively affected mucosal responses, suggesting that, contrary to the CD8-/- mouse gut, the normal gut mucosa may host CD8+ T cells that exert a local suppressive effect on T- and B-cell responses. The magnitude of the enhancing effect of CT was comparable in CD8-/- and normal mice, clearly demonstrating that the adjuvant mechanism of CT does not require CD8+ T cells. On the other hand, the adjuvant effect of CT required CD4+ T cells, because no or poor anti-KLH responses were observed in CD4-/- mice. In both normal and CD8-/- mice CT adjuvant promoted KLH-specific CD4+ T-cell printing without any selective effect on the differentiation towards a T-helper type-1 (Th1) or Th2 dominance. Furthermore, CT adjuvant increased the frequency of CD4+ T cells expressing a memory phenotype, i.e. CD44high, LECAM-1low and CD45RBlow. We have shown, using gene-targeted mice, that CD8+ T cells are not required for the adjuvant effect of CT, and that CD8+ T cells may exert local mucosal down-regulation of intestinal immune responses.
authors.affiliation: Department of Medical Microbiology and Immunology, University of Göteborg, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Hörnquist
authors.forename: D
authors.initials: D
authors.lastname: Grdic
authors.forename: T
authors.initials: T
authors.lastname: Mak
authors.forename: N
authors.initials: N
authors.lastname: Lycke
mesh_terms: D000276:Adjuvants, Immunologic; D000818:Animals; D000917:Antibody Formation; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D018929:Cell Culture Techniques; D002772:Cholera Toxin / Q000276:immunology*; D006433:Hemocyanins / Q000276:immunology; D007111:Immunity, Cellular; D007156:Immunologic Memory; D016130:Immunophenotyping; D007413:Intestinal Mucosa / Q000276:immunology*; D008222:Lymphokines / Q000096:biosynthesis; D051379:Mice; D008810:Mice, Inbred C57BL; D013154:Spleen / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D008222:Lymphokines; D002772:Cholera Toxin; D006433:Hemocyanins; C032808:keyhole-limpet hemocyanin