Modulation of pokeweed-mitogen-induced immunoglobulin secretion by human bronchoalveolar cells

The effects of human bronchoalveolar cells on pokeweed-mitogen-induced immunoglobulin(Ig) secretion in vitro were investigated, using a reverse hemolytic plaque assay. Unfractionated peripheral blood mononuclear cells from 7 nonsmoking normal subjects responded to pokeweed mitogen with a geometric mean of 6,550 Ig-secreting cells per million cultured mononuclear cells, whereas monocyte-depleted mononuclear cells responded with only 148 (p = 0.015, paired 2-tailed t test). The addition of 1 to 20% autologous bronchoalveolar cells to unfractionated mononuclear cells progressively suppressed the Ig-secretory response (p less than 0.01, paired t test comparing 0 to greater than or equal to 10% added bronchoalveolar cells). However, the addition of low concentrations of bronchoalveolar cells to monocyte-depleted mononuclear cells partially reconstituted the response to pokeweed mitogen, whereas the response with higher concentrations of bronchoalveolar cells was similar to background responses. Thus bronchoalveolar cells could modulate pokeweed-nitrogen-induced Ig secretion in different ways, depending on the pressure or absence of monocytes in the mononuclear cell population. The suppressor activities of bronchoalveolar cells were not abrogated by prior irradiation and were only partially reversed by the addition of indomethacin to the cultures. However, prior disruption of bronchoalveolar cells completely abolished their suppressive functions. Suppression of pokeweed-mitogen-induced Ig secretion is probably mediated by intact, radioresistant pulmonary alveolar macrophages.