Primary in vitro antibody response in humans: role of adherent cells in the development of haemolytic colonies.

Primary antibody response in vitro by human peripheral blood mononuclear cells (PBMC) against sheep red blood cells (SRBC) was investigated by the method of haemolytic colonies in soft agar. The response was modulated by two antagonistic populations of surface-adherent cells (AC) that could be enriched by physical means using differential adhesion to the plastic. Firmly adherent cells (AC/FA), which remained surface stuck after 18 hr, cocultured with AC-depleted PBMC, significantly inhibited the production of haemolytic colonies; AC/NR cells, which were released after this interval, strongly increased the response. The inhibition by AC/FA cells was mainly due to production of peroxides and the stimulation by AC/NR to the synthesis of arachidonic acid derivatives. When the two subpopulations were present contemporarily at the concentration shown in PBMC suspensions, the suppressive action of AC/FA overwhelmed the enhancing activity of AC/NR cells. Functional, histochemical and immunochemical data suggest that the AC/FA fraction is mainly composed of typical phagocytosing cells, whereas the AC/NR fraction contains cells of uncertain classification that do not exhibit active phagocytic activity.