Lipoprotein lipase secretion by human monocytes and rabbit alveolar macrophages in culture

Human peripheral blood monocytes and rabbit alveolar macrophages secreted lipoprotein lipase during culture. Within hours after plating, lipoprotein lipase had accumulated in the culture medium of monocytes, and the rate of accumulation increased with time in culture. The initial rate of secretion of lipoprotein lipase by alveolar macrophages was higher than in monocytes but decreased after 8--10 hr to values similar to those expressed by monocytes cultured for the same length of time. The enzyme was characterized as lipoprotein lipase (triacylglycero-protein acylhydrolase, EC 3.1.1.34) on the basis of pH optimum (7.8--8.2 for monocytes, 8.1 for alveolar macrophages), dependence on apolipoprotein C-II for activity, inhibition by 0.3--0.5 M sodium chloride and protamine sulfate, and retention of a heparin-Sepharose gel. The expression of lipoprotein lipase secretion by human monocytes may have important implications with respect to the development of foam cells in the arterial wall during atherogenesis.