Selective induction of enhanced complement receptor 3 activity on murine macrophages

Chemotaxis of the peritoneal cells and the detection of a chemo-attractant in the effluent from peritoneal dialysis patients

The migration of peritoneal cells from 25 continuous ambulatory peritoneal dialysis patients and eight healthy women undergoing laparoscopy were studied. Peritoneal cells of continuous ambulatory peritoneal dialysis patients migrated to commonly used chemoattractants, like N-formyl-methionyl-leucyl-phenyl-alanine-methyl- ester and casein, but they also migrated to high concentrations of recombinant interleukin-1 alpha and to endotoxin (lipopolysaccharide). In the peritoneal effluent from continuous ambulatory peritoneal dialysis patients a rather heat stable chemoattractant was found with a molecular weight of 40-200 kDa with an optimal activity at approximately 125 kDa. The chemoattractant is a protein and is not complement factor 5a or interleukin-1 and was only found in peritoneal effluent from continuous ambulatory peritoneal dialysis patients, but not in peritoneal fluid from healthy women undergoing laparoscopy. Therefore, peritoneal dialysis might induce the generation of a chemoattractant. The optimal chemotactic response of peritoneal cells from continuous ambulatory peritoneal dialysis patients to N-formyl-methionyl-leucyl-phenyl-alanine-methyl- ester in medium could be enhanced by replacing the medium by peritoneal effluent. So the chemotaxis of peritoneal cells to the factor in the peritoneal effluent is caused by another mechanism, which might involve different cell surface receptor populations, than the chemotactic response to N-formyl-methionyl-leucyl-phenyl-alanine-methyl-ester.

An in vitro system to study listericidal capacity of macrophages from separate mice: resident macrophages exhibit different activation patterns

An in vitro system with macrophages from individual mice was established to study their listericidal capacity. Because no antibiotics were used, bacterial killing was really due to macrophages in short-term culture. To restrict the extracellular growth of bacteria, cell culture medium was changed at 1-h intervals. We demonstrated that intracellular growth of listeria in macrophage pools from untreated animals varies considerably. Obviously, preactivated macrophages are constantly present, so that the common procedure of using macrophage pools from several animals is no longer acceptable. In addition, we demonstrated that in vitro mixtures of listeria-immune macrophages of one animal with cells from untreated animals at different ratios exhibit enhanced bacterial killing above a mere additive effect. Consequently, by using macrophages from individual untreated mice, we found that cells of different animals exhibited various activation stages, although unstimulated, inbred specific-pathogen-free mice of the same age, weight, and sex were used. When equal numbers of macrophages from untreated separate animals were mixed in vitro, intracellular growth of listeria was only moderate; that is, the number of preactivated macrophages of the individual animals determined listerial growth in the pooled preparation. Furthermore, we showed that identical doses of phorbol myristate acetate exerted different effects on the listericidal activities of macrophages as a function of their preactivation states. These experiments clearly demonstrate the advantage of using macrophages from individual mice for in vitro studies of macrophage activation.

Cell surface receptors for lactate dehydrogenase-elevating virus on subpopulation of macrophages

We examined the binding and internalization of unlabeled and 125I-labeled, purified lactate dehydrogenase-elevating virus (LDV) by peritoneal macrophages cultured in vitro. Upon incubation of the cells at 4 degrees C with greater than 100 ID50/cell, the virus was surface-bound on a small subpopulation of macrophages (about 5% of the total cells) as determined by electron microscopy, fluorescent antibody staining, and autoradiography of cells incubated with 125I-labeled LDV. At 37 degrees C, LDV particles were seen in intracellular endocytic vesicles also in about 5% of the cells, and the proportion of cells with virus-containing vesicles correlated with the proportion of cells which became productively infected with LDV as assessed by determining LDV RNA synthesis in individual cells and by fluorescent antibody staining. Pretreatment of the resident peritoneal macrophages with trypsin inhibited the binding of 125I-labeled LDV and the productive infection of the cells with the virus. After removal of the trypsin and incubation in complete medium, permissiveness for LDV reappeared after an 8-12 h lag, whereas Fc and C3 receptors reappeared more rapidly after trypsin treatment. Populations of resident peritoneal macrophages, starch-elicited peritoneal macrophages, splenic macrophages, and bone marrow macrophages contained a similar proportion of cells that could be productively infected with LDV. Little, if any, LDV replication was detected in cultures of lung, liver and peripheral blood macrophages as well as in thioglycollate-elicited and BCG-activated macrophages. We conclude that the permissiveness for LDV of resident peritoneal macrophages correlates with the presence of a trypsin-sensitive receptor present on a subpopulation of these cells. The identity of the receptor has not been definitively established. Treatment of macrophages with neuraminidase or various sugars had no significant effect on LDV replication. Lysis of I-A-positive macrophages with a monoclonal antibody and complement reduced the number of macrophages which could be productively infected by 50%, which suggests that macrophages lacking surface Ia can be productively infected with LDV in vitro.

Synthesis of complement by macrophages and modulation of their functions through complement activation

During the last decade considerable progress has been made to characterize intimate functional links between macrophages, a major cellular component of immunoinflammatory responses, and the complement system representing the major humoral mediator of inflammation. Macrophages of various species and tissue sites have been shown to synthesize and release most of the complement components providing these cells with their own "pericellular" complement system. Circumstantial evidence for the assembly of both classical and alternative pathway convertases has been adduced. An intricate network of feedback loops involving endogenous and extrinsic factors operates to adjust complement production to acute requirements, for example augmenting production in the face of accelerated turnover at sites of inflammation, and returning it to baseline levels once the inflammatory stimulus has subsided, in order to maintain a fine-tuned balance. The molecular mechanisms underlying regulation of complement synthesis by macrophages are beginning to be elucidated by use of gene technology. On the other hand, complement activation products exert a number of effects on macrophages via specific surface receptors causing internalization of offending agents, microbes, and immune complexes, promotion of intracellular killing, controlling migration behavior, inducing release of potent biologic substances such as lysosomal enzymes, arachidonic acid metabolites, and interleukin 1. In these interactions, two important humoral mediator systems of inflammation, the complement system and the arachidonic acid cascade, are functionally linked at the level of the macrophage. Stimulation of the release of immunomodulating compounds from macrophages invoke a role for complement in immune regulation. This multifaceted interplay is of particular importance considering the mobility of macrophages that allows them to gain almost unrestricted access to sites of ongoing immunoinflammatory responses. The time seems to have come to abandon the petrified thinking in socalled systems as, for instance, humoral versus cellular, specific versus unspecific, and to proceed to interlocking functions guided by physiology proper.

Dynamics of cytochemically distinct subpopulations of macrophages in elicited rat peritoneal exudates

Qualitative and quantitative changes in rat peritoneal macrophage (M phi) subpopulations, differing in their ultrastructural peroxidatic staining characteristics were followed over the course of a thioglycollate (TG) broth-induced inflammatory response. In addition, selected functional features of the normal steady-state and 4-day TG-induced populations of M phi were compared. The steady-state population consisted primarily of M phi with peroxidatic staining limited to the nuclear envelope (NE) and rough endoplasmic reticulum (RER); such cells are called resident M phi. Within hours of TG injection, there was an influx of monocyte-derived exudate M phi, the number of which reached a maximum, by 24 hr. During the next 24 hr, the proportion of exudate M phi decreased with a concomitant increase in peroxidatic activity (PA)-negative M phi. These two cell types continued to predominate for the next 48 hr during which there was a gradual increase in resident M phi and so-called "exudate-resident" M phi, the latter of which exhibits both exudate and resident PA patterns. Thus, the 4-day TG-induced population consisted of four cytochemically distinct M phi subpopulations: approximately 50% PA-negative M phi, approximately 25% exudate M phi, approximately 15% resident M phi, and approximately 10% exudate-resident M phi. Differences in Fc receptors and complement receptors 1 and 3 were noted between the two populations in the presence of progenitors that give rise to colonies of M phi in liquid culture in response to murine-derived colony-stimulating factor 1. The implications of these results in regard to the origin(s) of M phi diversity are discussed.