Direct and indirect allorecognition.

The design and effectiveness of strategies to promote long-term graft acceptance requires a fundamental understanding of the mechanisms underlying acute and chronic rejection. This chapter discusses the two pathways of allorecognition--direct and indirect--and suggests that the direct pathway plays a major role in the early weeks after transplantation and that the indirect pathway may contribute to the process of chronic rejection. The results of in vitro and in vivo experimental models are discussed, together with clinical data.