Cross-presentation, dendrttic cells, tolerance and immunity

This review examines the role of cross-presentation in tolerance and immuni ty. We discuss (a) the antigenic requirements for cross-presentation, (b) t he phenotype of the antigen presenting cell (APC), (c) the cellular interac tions and molecular signals involved in cross-priming, and (d) the factors that direct the immune system toward tolerance or immunity. A large part of this review is dedicated to summarizing our current knowledge of the cross -presenting APC.