Phagocytotic processing of apoptotic bodies of transitional ameloblasts by MHC Class II-expressing macrophages in rat incisor.

We examined the processing of apoptotic ameloblast fragments at the transitional stage by immunocytochemistry and electron microscopy. Both macrophages and epithelial cells in the enamel organ ingested apoptotic bodies. MHC Class II antigen expression and the phagolysosomal nature of the macrophages were further examined by immunoelectron microscopy using OX6 and ED1 antibodies followed by HRP- or gold-conjugated secondary antibodies. The results showed that macrophages in the enamel organ at the transitional stage expressed MHC Class II antigens at their plasma membranes and that the same cells contained apoptotic fragments in ED1-positive vacuoles. We suggest that diverse immunological responses, such as the self-antigen presentation, may be invoked in the process of apoptosis.