DENDRITIC CELLS IN THE T-CELL AREAS OF LYMPHOID ORGANS

Substantial numbers of dendritic cells (DCs) are found in the T-cell a reas of peripheral lymphoid organs such as the spleen, lymph node and Peyer's patch. By electron microscopy these DCs (also called interdigi tating cells) form a network through which T cells continually recircu late. The cytological features of DCs in the T-cell areas, as well as a number of markers detected with monoclonal antibodies, are similar t o mature DCs that develop from other sites such as skin and bone marro w Some markers that are expressed in abundance are: MHC II and the ass ociated invariant chain, accessory molecules such as CD40 and CD86, a multilectin receptor for antigen presentation called DEC-205, the inte grin CD11c, several antigens within the endocytic system that are dete cted by monoclonal antibodies but are as yet uncharacterized at the mo lecular level, and, in the human system, molecules termed S100b, CD83 and p55. DCs in the periphery can pick up antigens and migrate to the T-cell areas to initiate immunity. However, there are new observations that DCs within the T-cell areas also express high levels of self-ant igens and functional fas-ligand capable of inducing CD4(+) T-cell deat h. We speculate that there are at least 2 sets of DCs in the T-cell ar eas, a migratory myeloid pathway that brings in antigens from the peri phery and induces immunity, and a more resident lymphoid pathway that presents self-antigens and maintains tolerance.