Some chemical and metabolic characteristics of polymorphonuclear leukocytes and monocytes from peritoneal exudates of the guinea pig, and of alveolar macrophages from the same animal, have been compared. Changes in the metabolic patterns of these three types of cell have been followed during the act of phagocytosis. The effect of conventional inhibitors of metabolism, and of anaerobiosis on the phagocytic ability of each of the three cell types mentioned has also been determined. From these studies it was found that alveolar macrophages depend to a considerable degree upon oxidative phosphorylation to provide energy for phagocytosis. The other two types of cell depend only on glycolysis as the source of metabolic energy for that function. In some experiments aimed at obtaining information on the possible role of complex lipids in the function of the cell membrane, it was noted that phagocytosis stimulated the incorporation of inorganic phosphate-P 32 into the phosphatides of both types of cell from peritoneal exudates--whether these were free-swimming or adherent to a surface. This phenomenon has not yet been detected in the case of alveolar macrophages.During the past several years, a number of studies have been carried out on the metabolic concomitants of the phagocytic act in leukocytes. Almost all of these observations were made on polymorphonuclear leukocytes. Only a few data have been reported for monocytes (1-4). The object of the present experiments was to examine the metabolic basis of the phagocytic event in mononuclear cells and in alveolar macrophages and to compare these cells with polymorphonuclear leukocytes. This seemed to be of importance, because, although polymorphonuclear leukocytes are the most immediate phagocytizing cells during infection, they are very short-lived. The macrophages, of which the peritoneal mon0nuclear leukocytes and the alveolar macrophages may be representative, are of major importance as defenses against invading organisms. Alveolar macrophages are particularly intriguing cells and have recently been the subject of considerable morphological study (5). There has been a good deal of discussion of their origin (5-8) and function (6,8).This paper presents information on the chemical characteristics of these three types of phagocyte, all obtained from the guinea pig, as well as comparisons of the metabolic changes which accompany phagocytosis. Definite differences with respect to the source of metabolic energy for phagocytosis, between the alveolar macrophages on the one hand and the peritoneal exudate monocytes and polymorphonuclear leukocytes on the other, were found.

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