The lymphocyte-dendritic cell system.

Antigens provoke immune responses. The group of immunocompetent cells related directly to this response includes T and B cells, macrophages (M phi) and dendritic cells (DCs). DCs acting as antigen-presenting cells have been recently recognized to be important in initiating the immune response. B cells and follicular dendritic cells (FDCs), the major immunocompetent cells in the B-cell dependent area, play an important role in humoral immunity, while T cells and interdigitating cells (IDCs), which are the major immunocompetent cells in the T-cell dependent (TD)-area, play an important role in cellular immunity. The B cell-IDC interaction in the TD-area is also essential for the B-cell response against TD-antigen. Consequently, the lymphocyte-DC interaction is essential in the response to antigenic stimulation and in inducing the potent effector cells. B cell-DC, T cell-DC and DC-B cell-T cell interactions are regulated in predetermined sites by complex and varied mechanisms. Much recent evidence demonstrates that DCs modulate lymphocyte biology in its broadest aspects, including generation, differentiation, proliferation, and activation. In this review, we outline recent studies on the generation, structure, and function of lymphatic tissues, propose the concept of the "Lymphocyte-Dendritic Cell System (LDS)", and finally describe the significance and functions of this system in health and disease.