Phagocytosis plays a major role in the defence of higher organisms aga
inst microbial infection not only by allowing ingested microbes to be
destroyed by microbicidal mechanisms, but also by providing the basis
for processing of their antigens to forms that generate immune respons
es. This article examines the role of the phagolysosome in antigen pro
cessing, and discusses the contributions of both MHC class II ann MHC
class I molecules to the presentation of antigens derived from phagocy
tosed material.