A comparison of the stimulatory activities of lymphoid dendritic cells and macrophages in T proliferative responses to various antigens.

The identities of murine accessory cells and the mechanism by which they process antigen and stimulate T cell proliferation have been examined with cell separation techniques and specific agents to block antigen catabolism. Using preparations of splenic dendritic cells (DC) and macrophages (M phi) with minimal cross-contamination, we found that only DC could induce syngeneic mixed leukocyte reaction (MLR), whereas both DC and M phi could initiate allogeneic MLR. This observation may have significant implications for syngeneic MLR as a manifestation of self Ia recognition, and for the cell type that defines self Ia during ontogeny. DC and M phi could present soluble antigens such as purified protein derivative of tuberculin (PPD) and Salmonella flagellin about equally well to antigen-specific T cell lines. M phi, however, were much more effective than the non-phagocytic DC at inducing T cell proliferation to whole Corynebacterium parvum organisms. These differences could not be attributed to differences in antigen uptake. The results suggest that the bacteria must be ingested and processed by phagocytes before T cell activation. Using the lysosomotropic agent chloroquine to inhibit antigen catabolism in accessory cells, we found that the presentation of large antigens by M phi and DC was abolished by chloroquine treatment, whereas T cell activation by antigens (such as PPD or integral membrane Ia for MLR) that apparently required no processing was relatively insensitive to chloroquine. Thus, in addition to differences between cells, discrete functions within each cell type can also be distinguished.