Human T cell proliferative responses to particulate microbial antigens are supported by populations enriched in dendritic cells.

The efficacy of dendritic cells in antigen presentation was studied in eight healthy subjects using a lymphoproliferation assay. Both particulate (Mycobacterium leprae, H37Ra) and soluble (PPD, tetanus toxoid) bacterial antigens were used as stimulants over a concentration range of accessory cells (monocytes (MO) and dendritic cells (DC)) varying from 10 to 0.1% in co-cultures using T-enriched cells. In general, co-cultures with T + MO and T + DC at all concentrations of accessory cells showed significant improvement of antigen-induced lymphoproliferation over PBMC cultures. The improvement in delta ct/min of T + DC co-cultures as compared to T + MO with parallel concentrations of accessory cells (P less than 0.05 to less than 0.01) was significant. Of the bacterial antigens used to test the antigen-presenting ability of DC, the particulate antigen (H37Ra) showed the most impressive improvement (380%) of T cell proliferation in DC reconstituted cultures as compared to monocytes. PPD, soluble protein derived from a similar tuberculosis strain of mycobacteria, was not presented as effectively as the particulate equivalent even though the donors of the appropriate cell combinations showed skin test reactivity to this antigen.