Antibody responses to T-dependent antigens: contributions of dendritic cells and helper T lymphocytes.

Dendritic cells (DC) are important accessory cells for T-dependent antibody formation. Other leukocytes -- such as macrophages and B cells -- do not independently initiate antibody responses. DC induce the two principal functions of helper T cells, i.e., direct activation of small, antigen-specific B cells, and release of B cell stimulating factors. These two helper functions can operate in tandem during the 1 degree response to hapten-carrier conjugates. Once the helper cell is sensitized in concert with DC, it interacts directly with B cells apparently in the absence of DC. These functions of helper cells all occur in discrete aggregates which contain DC and the appropriate responding lymphocytes. The DC/lymphocyte aggregates likely represent the appropriate structural unit for the study of cell-cell interactions during antibody responses.