The effect of adherent and phagocytic cells on human lymphocyte PHA responsiveness

The effect of small numbers of adherent and phagocytic cells on the human peripheral blood lymphocyte response to PHA was examined by depleting these cells from lymphocyte preparations. Lymphocyte preparations obtained by centrifugation on Ficoll--Triosil, which contained on average 85% lymphocytes, responded well to PHA. Depletion of cells adhering to nylon fibre, giving a population containing on average 95% lymphocytes, resulted in a considerably reduced response. Depletion of cells that adhered to plastic or ingested iron powder to give populations containing on average 90% lymphocytes, also reduced the PHA response, but to a lesser extent. Reduction in PHA responsiveness correlated with increasing lymphocyte purity. The responsiveness of nylon-column-filtered cells could be restored by adding a small number of cells from a monocyte-rich population.