David B. Drath

BIOCHEMICAL CHARACTERISTICS OF ACTIVATED MACROPHAGES

In the inflammatory processes that occur in rheumatoid arthritis, it is clear that granulocytes play a large role. Macrophages are also present, and the importance of their contribution will presumably be fully comprehended only when their physiologic characteristics in the particular environment are defined. They may be activated to varying degrees. Specific activation is due to phenomena with an immunologic basis; in addition, macrophages may be stimulated by nonspecific means. The definition of “activated” macrophages is a functional one, which indicates that such cells are more efficient with respect to their overall phagocytic and/or antimicrobial activities than are control macrophages. “Activated” macrophages were described mainly by Mackaness in the 1960~. ’ -~ The activation observed has, as mentioned, a specific immunologic basis and is mediated by lymphocytes, but the activated cells manifest their enhanced microbicidal action nonspecifically : that is, they exhibit an augmented capacity to deal not only with the original “activating” organism but also with other organisms. One organism often used for activation of macrophages is Listeria monocytogenes. About 1 week after infection of mice with this bacterium, the peritoneal macrophages may be harvested in markedly greater quantities than is normally the case. They spread out on glass more than do normal macrophages, and they are more phag~cyt ic .~ It is not yet clear whether their enhanced antimicrobial action is due simply to the greater phagocytic ability or whether they have an armamentarium of antimicrobial agents or systems that is qualitatively or quantitatively different from that of control cells. In the context of this Conference, manifestation of antimicrobial potentiat is of minor importance-the capacity to ingest (phagocytize or pinocytize) and destroy tissue components is the important issue. Of concern is the possible activation of macrophages by lymphocytes sensitized to tissue components or their degradation products. Further, macrophages may also be directly (nonspecifically) activated by substances in the synovium, for example. The particular burden of this paper is to indicate some of the biochemical properties of specifically and nonspecifically activated macrophages as compared to control ce1ls.t In addition, one may also compare “resting” and

Tobacco smoke. Effects on pulmonary host defense.

Tobacco smoke affected both the metabolism and function of pulmonary alveolar macrophages (PAM). Phagocytosis of viable Staphylococcus aureus and inert starch particles was minimally but consistently depressed in PAM from rats exposed to tobacco smoke for six months. Oxygen consumption, superoxide and hydrogen peroxide release, and hexose monophosphate shunt activity were elevated in cells from smokers. Oxidation of glucose, labelled in the carbon-six position, remained unchanged. All observed effects of tobacco smoke on oxygen metabolism occurred during phagocytosis and did not affect the basal metabolism of the nonstimulated cell.Tobacco smoke affected both the metabolism and function of pulmonary alveolar macrophages (PAM). Phagocytosis of viableStaphylococcus aureus and inert starch particles was minimally but consistently depressed in PAM from rats exposed to tobacco smoke for six months. Oxygen consumption, superoxide and hydrogen peroxide release, and hexose monophosphate shunt activity were elevated in cells from smokers. Oxidation of glucose, labelled in the carbon-six position, remained unchanged. All observed effects of tobacco smoke on oxygen metabolism occurred during phagocytosis and did not affect the basal metabolism of the nonstimulated cell.

Tobacco smoke and the pulmonary alveolar macrophage.

Our results indicate that tobacco smoke exposure to varying duration causes morphological, biochemical and functional alterations in pulmonary alveolar macrophages. The results of these changes is a population of alveolar macrophages made up of larger cells, with a reduced nucleus-cytoplasmic ratio, which are heavily loaded with heterolysosomes containing lipid. Though their fractional complement of mitochondria remains the same, an increase in the inner mitochondrial membrane surface area may be related to an enhanced oxidative metabolism. The cell is biochemically activated particularly following chronic exposure and is functionally impaired with respect to phagocytosis.

Biochemical aspects of the function of the reticulo-endothelial system.

The title of this presentation was assigned, and it is truly doubtful whether we can present a picture that is consistent with the assignment. The reasons for this are manifold. First, the reticulo-endothelial system per se, as it was defined by Aschoff (1) is a broader group of cells than we are competent to discuss. Indeed, we find ourselves much more comfortable with the concept of the “mononuclear phagocyte system” proposed at the conference on Mononuclear Phagocytes in Leiden, 1969 (18). The system, as described there, is concerned with mononuclear phagocytes, a group of cells that are related in morphology, functions and origin, ranging from the promonocytes through the monocytes of the blood to the macrophages of the tissues, including histiocytes, Kupffer cells, the alveolar macrophages; macrophages of the spleen, lymph nodes, bone marrow, peritoneum and bone tissue; and the microglia of the nervous system. Obviously there is overlap between the two classifications. What we shall have to say in this report will focus largely on the macrophage as it is obtained by simple lavage from the peritoneal cavity; from the peritoneal cavity after elicitation with an agent such as caseinate; or as it is washed out of the alveoli. It is not that biochemical studies have not been performed on other cells of this system--there have been such studies, e.g., on the Kupffer cells of the liver, but these studies are relatively few and perhaps more difficult to interpret than experiments on defined cell populations.

The effects of clofibrate ingestion on alveolar macrophage peroxisome content and oxygen metabolism

Respiratory burst activity in alveolar macrophages in response to particulate and soluble challenges, such as zymosan particles and phorbol myristate acetate (PMA), is not nearly as dependent upon membrane stimulation as in neutrophils. Microperoxisomes are subcellular organelles containing catalase and are present in lung macrophages and cells of other organs. Evidence from liver cells indicates that peroxisomes are intimately involved with hydrogen peroxide and lipid metabolism. Clofibrate (2-(p-chlorophenoxy)-2-methylpropionic acid ethyl ester, Atromid-S-®), a hypolipidemic drug known to cause peroxisomal proliferation in liver cells, was studied with respect to its ability to cause increases in the microperoxisome content and to alter the cellular metabolism of alveolar macrophages. Liver weight increased over a 2-week drug treatment period while lung weight remained unchanged. Plasma triglyceride levels were decreased by the treatment, indicating the effectiveness of the drug. Unlike the effect on liver cells, however, clofibrate did not cause a proliferation of microperoxisomes, as determined by morphometric analysis. Oxygen concumption and hydrogen peroxide generation by alveolar macrophages in response to either stimulant (zymosan or PMA) was no greater in clofibrate-treated rats than in controls. Superoxide release, when expressed as the change in response to PMA, appeared elevated in the drug group; statistical significance, however, was not demonstrated. The hexose monophosphate shunt (HMP), which produces reducing equivalents for lipid biosynthesis, was elevated in macrophages from clofibrate-treated rats when expressed similarly. The significance of these results is discussed in relation to the known effects of the drug on liver cells.