Role of CD8 alpha(+) and CD8 alpha(-) dendritic cells in the induction of primary immune responses in vivo

Data from adoptive transfer of mature dendritic cells (DC) indicate that th ey are responsible for the induction of primary immunity. Two subclasses of DC have been recently identified in spleen that differ in their phenotype and in certain regulatory features. In vitro, both subsets have the capacit y to activate naive T cells, although CD8 alpha(+) DC have been shown to in duce T cell apoptosis and to stimulate lower levels of cytokines compared w ith CD8 alpha(-) DC. The objective of this study was to analyze the functio n of these distinct DC types in vivo, Our results show that both subsets, p ulsed extracorporeally with antigen and injected in the footpads of syngene ic mice, sensitize an antigen-specific T cell primary response. However; CD 8 alpha(+) cells trigger the development of Th1-type cells, whereas CD8 alp ha(-) DC induce a Th2-type response. These observations suggest that the Th 1/Th2 balance in,in vivo is regulated by the antigen-presenting-cells of th e primary immune responses.