Kinetics of phagocytosis of Staphylococcus aureus by alveolar and peritoneal macrophages

Antibody binding to porcine sialoadhesin reduces phagocytic capacity without affecting other macrophage effector functions

Sialoadhesin (Sn) is a macrophage-restricted endocytic receptor involved in cell-cell, cell-matrix and cell-pathogen interactions. Recently, porcine Sn (pSn) was shown to be involved in signaling and lately Sn is gaining interest as a potential target for immunotherapy. However, little is known about the effect of ligand binding to Sn on macrophage effector functions. In this study, we tested the effect of antibody binding to pSn on macrophage viability, phagocytosis of microspheres, uptake and processing of soluble antigens, reactive oxygen/nitrogen species production, MHC I and MHC II cell surface expression and cytokine production. This was done by treatment of porcine primary alveolar macrophages with the pSn-specific mAb 41D3, or an isotype-matched control mAb. No significant effect on most effector functions under study was observed, except for a significant reduction of phagocytosis. Thus, antibody binding to pSn can downregulate phagocytosis, which could have implications on homeostasis, infectious and immune diseases, and immunotherapy.

Development of mathematical models for an in vitro-phagocytosis test system

Phagocytosis tests have been carried out by many authors using different methods under different conditions. The results have been interpreted in different ways, as well sometimes with conflicting notations. In order to get to a more systematic data analysis and to separate intrinsic from methodic influences, the possibility to apply mathematical models to a phagocytosis test has been studied. In agreement with previous experiences that phagocytosis can well be represented by a mathematical treatment as Michaelis-Menten-type enzyme kinetics concerning its initial rate and by an exponential function under in vivo conditions, in vitro-phagocytosis was phenomenologically described as an analogon of an irreversible bimolecular chemical reaction. In this way, rate and capacity of phagocytosis may be quantified separately. On the basis of systematic deviations of the data from this model, modifications have been developed which could be connected with pertinent observations. The design of further experiments from preliminary results on the basis of our models is discussed.

Intrapulmonary growth of Staphylococcus aureus in rats during induced atelectasis

Intrinsic pulmonary antibacterial defenses are mediated by alveolar macrophages and by noncellular factors. Mechanical ventilation in the resting tidal volume range leads to alterations in the physical characteristics of alveolar surfactant, alveolar instability, regional hypoxia, and systemic hypoxemia. While a number of experimental manipulations diminish the activity of the intrinsic antibacterial defense system, the effects of mechanical ventilation per se have not been systematically evaluated previously. We found that normal rats ventilated without sighing (periodic large breaths) manifested severe defects in pulmonary clearance of Staphylococcus aureus during 6-h experiments, such that growth of the inoculum occurred. Addition of a timer-controlled mechanism to cause the animals to sigh every 2 min, without other modifications in the experimental conditions, caused significant improvement in clearance. Analysis of cellular response, compartmentalization of viable bacteria, surfactant quantities and sedimentation characteristics, and protein influx indicated that the defect in clearance paralleled alterations in the physical state of surfactant and alveolar stability but was not strongly correlated with alterations in the other parameters we measured. The data show that defective pulmonary bacterial clearance is rapidly induced by measures which alter alveolar stability and suggest that intrinsic pulmonary defenses require maintenance of normal air-liquid interfaces for optimal function.

Defective mononuclear phagocytic function in mice homozygous for the cribriform degeneration autosomic recessive mutation

Decreased lung clearance of Staphylococcus aureus has been reported in mice homozygous for the cribriform degeneration (cri) autosomal recessive mutation. In the present study, the phagocytic capacities of alveolar and peritoneal macrophages were quantitated by applying kinetics of the first order reaction criteria. The characteristics of the pulmonary and peritoneal mononuclear cell populations from mutant and control mice were indistinguishable. The kinetic assays revealed decreased phagocytosis work in both alveolar and peritoneal macrophages from cri/cri mice. The results lend support to this mutation as a possible model system to study the early stages of lung disease physiopathology in cystic fibrosis.

Effects of antiviral agents on murine cytomegalovirus-induced macrophage dysfunction

Infection of murine peritoneal macrophages with murine cytomegalovirus (MCMV) led to disruption of phagocytosis. This alteration of cellular behavior appeared to be an early event in viral replication appearing 24 to 36 h before virus production and 84 to 108 h before cell death. The effects of a variety of antiviral agents on both MCMV replication and MCMV-induced depression of phagocytosis were evaluated in vitro. Although all compounds thought to act by preventing viral DNA replication inhibited MCMV replication in macrophages, none prevented expression of virus-induced alteration of phagocytosis. Cycloheximide at 1 microM blocked viral replication and viral antigen expression and prevented depression of phagocytic activity.

Modulation of bacterial association to HeLa cell cultures by cell density and by chlamydial infection

The effect of cell density on the rate of association of Escherichia coli and Staphylococcus aureus by monolayer cultures of HeLa 229 cells was investigated. Radioactively labeled bacteria were incubated with sparsely and densely plated cells. The rate of bacterial uptake was 10- to 20-fold higher in sparse cultures. Kinetic analysis of data with different multiplicities of input bacteria showed that the Km of the reaction was unaltered, whereas the Vmax was inversely related to cell density. Pretreatment of HeLa cultures with dibutyryl adenosine 3',5'-phosphate had little effect on the rate of bacterial association. The simultaneous presence of an obligately parasitic bacterium, Chlamydia trachomatis LGV434, enhanced the Vmax of association of E. coli and S. aureus. This effect was more pronounced in dense HeLa cell cultures. Heat-inactivated chlamydiae were unable to modify the association. Enhanced association persisted for at least 3 h after infection with chlamydiae.

Replication of murine cytomegalovirus in lung macrophages: effect of phagocytosis of bacteria

Murine cytomegalovirus was found to replicate in lung and peritoneal macrophages of both CF-1 and BALB/c mice in vitro. Cytopathic changes typical of cytomegalovirus infection, including intranuclear inclusions, developed within the infected cells and eventually resulted in death of infected macrophages. Viral antigens were demonstrable by indirect immunofluorescence microscopy, and morphologically typical herpesvirus particles were observed in both nuclei and cytoplasm of murine cytomegalovirus-infected macrophages. Within 24 h after infection, at which time there was expression of viral antigens but no marcophage death, murine cytomegalovirus-infected macrophages demonstrated marked inhibition of phagocytosis of Staphylococcus aureus. Direct inhibition of macrophage function by cytomegalovirus infection in vivo could impair pulmonary defenses and may account in part for the frequent association of cytomegalovirus infection with other infectious agents.