Cellular synergy in the manifestation of accessory cell activity for in vitro antibody response.

The accessory cell (A-cell) activity of murine splenic adherent cells (SAC) and peritoneal exudate cells (PEC) for in vitro anti-SRBC and anti-DNP-KLH antibody responses of spleen lymphoid cells was abolished by the depletion of Ia+ cells from SAC and PEC by treatment with anti-Ia alloantiserum plus complement. The surviving Ia- macrophages in SAC and PEC were incompetent to achieve the A-cell activity. We prepared a crude and a further purified nonmacrophage cell fraction (termed CF and NMF). Nearly 70% of CF cells and more than 90% of NMF cells were Ia+ cells. The mature macrophage content of CF was less than 2%, and that of NMF was virtually negligible; suspected dendritic cells were contained at 5 to 10% in CF and 20 to 30% in NMF. The majority of cells in CF and NMF were lymphoid cells. This offered no problem in these experiments, since CF and NMF were added to lymphoid cells, in order to investigate the A-cell activity, usually in a ratio of 1 to 100. Neither CF nor NMF was adequate by itself to manifest the A-cell activity. However, the combination of either CF or NMF with Ia- macrophages resulted in the development of high A-cell activity. This did not occur with use of CF depleted of Ia+ cells or of NMF treated with anti-Ia without complement. These results indicated that the synergy between Ia- macrophages and Ia+ cells, most probably Ia+ nonmacrophage cells, was effective in developing the A-cell activity. It was also found that the interaction between the lymphoid cell and the Ia+ participant in the A-cell activity was genetically restricted, but Ia- macrophages functioned across the H-2 barrier.