Role of phagocytosis in the activation of macrophages

Abstract

Macrophages are found in large numbers at sites of chronic inflammation . They enter the lesions as monocytes (1) and develop in situ into large cells which synthesize and release an impressive variety of enzymes such as lysosomal hydrolases (2, 3), plasminogen activator (4), elastase (5), and collagenase (6) . These enzymes are most likely involved in the extensive destruction of cellular and extracellular tissue elements which accompanies chronic inflammation .Since macrophages are highly phagocytic, we have investigated the role of phagocytosis in their activation . We have studied the activation process in cultures of mouse peritoneal macrophages which were exposed to different types of particles . We have followed macrophage activation by assaying, in the cells as well as in the culture media, a number of enzyme activities which are known to change in the course of this process . In this paper, we present experiments which show that macrophages obtained from untreated mice become activated in culture after phagocytosis of zymosan or formaldehyde-treated sheep erythrocytes but do not become activated after phagocytosis of latex beads . Materials and MethodsMacrophage Cultures. Macrophages were obtained from male OF1 mice (Sandoz Ltd., Basel, Switzerland) weighing 20-24 g . The mice were either untreated, or treated 4 days before cell harvesting with Brewer's thioglycollate broth or a suspension of streptococcus A cell wall fragments (3) . The cell culture techniques and the biochemical assay methods used were described in an earlier paper (3) .Phagocytosis . Particles were prepared as follows . Zymosan (Koch-Light Laboratories Ltd ., Colnbrook, Buckinghamshire, England) was boiled in phosphate-buffered saline (PBS) l for 1 h, washed three times by centrifugation, resuspended in PBS (50 mg/ml), and autoclaved at 120°C (7) . Latex beads, 1 .01 ftm in diameter (Serva GmbH & Co., Heidelberg, W . Germany), were suspended in PBS containing 0 .01% Tween 80, washed three times by centrifugation, resuspended in PBS/Tween 80 and irradiated with ultraviolet light before use (8) . Sheep erythrocytes were washed five times in PBS by centrifugation, resuspended in PBS containing 3% formaldehyde for 2 days at 4°C, and then washed five more times in PBS (9) .Phagocytosis experiments were performed on cells which were allowed to adhere to the culture dishes at 37°C during 3 h after harvest . Particles were added in a small volume of PBS to the culture dishes (60 mm) containing 4-6 X 106 adherent cells and 3 ml of medium (3) . The particle-to-cell ratios were between 7 and 30 :1 for zymosan (see figures for details), 5 :1 for formaldehyde-treated sheep erythrocytes, and 40 :1 for the latex beads . Phagocytosis was stopped after 1 h by draining the medium and eliminating noningested particles by washing three times with PBS . Culturing in particle-free medium was then continued for up to 13 days under standard conditions (3) . The medium was changed at different intervals but at least every 3rd day .' Abbreviations used in thi...

Phagocytosis Stimulates the Release of a Slow Reacting Substance in Cultured Macrophages

“…Phagocytosis is the main function of macrophages. It is also a powerful stimulus of macrophage activation (Schnyder & Baggiolini, 1978b) as shown by the greatly increased oxygen metabolism and hexose monophosphate shunt activity (Karnovsky, Lazdins & Simmons, 1975), release of products of arachidonic acid metabolism (Humes, Bonney, Dahlgren, Sadowski, Kuehl & Davis, 1977;Brune, Glatt, Kalin & Peskar, 1978), and induction of secretion of lysosomal hydrolases and neutral proteinases (Schnyder & Baggiolini, 1978b). Our data indicate that, in macrophages activated by phagocytosis, arachidonic acid is metabolised to a significant extent through the lipoxygenase pathway.…”

Complement Proteins and Macrophages

“…Schnyder and Baggiolini reported the inability of latex to cause "macrophage activation" (6). We showed that the ingestion of latex in a particle to cell ratio range of 5 to 40 did not significantly affect either factor B or other enzyme secretion.…”

“…On the other hand, the synthesis of intracellular lactic dehydrogenase by zymosan-ingesting macrophages did not show an initial suppressive response but increased without a lag. It is known that, when macrophages ingest particles such as zymosan, a large quantity of enzymes escapes from lysosomes fused with phagocytic vacuoles (6,7). Therefore, one possible explanation for the early suppression of factor B secretion is that the more zymosan particles the macrophage ingests, the less factor B and lysosomal enzymes are retained by the macrophages at the beginning of cultivation.…”

“…Zymosan (Sigma, London Chemical Co., Ltd.) and latex beads (Difco Laboratories) were prepared according to the method of Schnyder and Baggiolini (6). Phagocytosis experiments were performed with macrophages previously cultivated for 2 hr.…”

“…This effect of LPS paralleled the secretion of acid phosphatase, indicating that the effect was one of the phenomena elicited by "LPS-activated macrophages." On the other hand, macrophages are known to be activated after phagocytosis of some particles such as zymosan, and as a result release a large quantity of lysosomal enzymes (6,7).…”