Protein biosynthesis by the pulmonary alveolar macrophage. Comparison of synthetic activity of suspended cells and cells on surfaces.

An effort to optimize conditions for studying protein biosynthesis by the pulmonary alveolar macrophage in vitro has led to a comparative analysis of the activity of suspended and adherent cells. A number of differences were observed. (1) Suspended cells synthesized protein for only a limited period of time, after which they responded only partially to incubation in fresh medium. This was true even under reincubation conditions in which the cells were allowed to adhere to a surface. Adherent cells, however, synthesized protein during a longer period of time and were fully capable of responding to new medium within the time periods examined. (2) Analyses of the radioactive proteins synthesized using a dual-isotope technique suggested that, during a period of 2 hours, suspended cells synthesized relatively smaller quantities of high molecular weight proteins than adherent cells. (3) The administration of a phagocytic load (zymosan; particle to cell ratio, 10:1) inhibited by 20 per cent the incorporation of isotopic amino acid into protein during a period of 3 hours. The same phagocytic load, however, stimulated incorporation by 20 per cent in adherent cells. (4) The rate of particle uptake measured using oil red O-albumin complexes decreased by approximately 50 per cent in suspended cells preincubated for 2 hours, but was maintained in similarly preincubated adherent cells. It was concluded that pulmonary alveolar macrophages incubated adhered to a surface are more appropriate for metabolic studies than are pulmonary alveolar macrophages incubated in suspension.