Related Experiment Videos
Direct activation of human polymorphonuclear leukocytes by Pseudomonas aeruginosa
G T Mai1, W K Seow, J G McCormack
1Department of Child Health, University of Queensland, Mater Public Hospital, South Brisbane, Australia.
Abstract:
Brief exposure of polymorphonuclear leukocytes (PMNs) to unopsonized Pseudomonas aeruginosa resulted in significant enhancement of PMN adherence and 3H-deoxyglucose uptake, two important indicators of PMN activation. Dose-response and time-course experiments show that maximal stimulation of PMNs occurred at a PMN: bacteria ratio of 10:1 and exposure time of 10 min. The PMN-stimulatory capacity of P. aeruginosa was completely or partially abolished by treatment with formalin, heat, ultrasonication and ultraviolet (UV) irradiation, all of which affect the integrity of ligands on the bacteria surface. The putative glycoprotein ligand(s) contains galactose rather than glucose as shown by the ability of galactose in the medium to abrogate PMN-stimulatory activity. This PMN-stimulatory activity was not mediated by soluble factor(s) released from either P. aeruginosa or PMNs as shown by experiments with appropriate supernatants. Finally, PMN-stimulating activity was also observed with P. maltophilia and P. pseudomallei, but not by the other Pseudomonas spp. such as P. cepacia and P. fluorescens. These results suggest that P. aeruginosa and other Pseudomonas spp. may have little capacity to circumvent PMN host defences. This may account in part for their limited pathogenic role as opportunistic micro-organisms, for the severe inflammatory lesions seen in Pseudomonas infections when they do occur, and is consistent with the fact that infection with these organisms is commonly associated with impaired quantity or function of PMNs.
Insights
Brief exposure to Pseudomonas aeruginosa activates polymorphonuclear leukocytes (PMNs), enhancing adherence and glucose uptake. This bacterial interaction suggests a limited capacity of Pseudomonas species to evade crucial host immune defenses.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Polymorphonuclear leukocytes (PMNs) are critical immune cells involved in host defense against bacterial infections.
- Pseudomonas aeruginosa is an opportunistic pathogen known to cause severe infections, particularly in immunocompromised individuals.
Purpose of the Study:
- To investigate the interaction between unopsonized Pseudomonas aeruginosa and PMNs.
- To identify the mechanisms underlying PMN activation by Pseudomonas species.
- To assess the role of bacterial surface ligands in this interaction.
Main Methods:
- Dose-response and time-course experiments were conducted to determine optimal conditions for PMN activation.
- Bacterial treatments including formalin, heat, ultrasonication, and UV irradiation were used to probe the nature of the stimulatory ligands.
- Galactose's effect on PMN activation was assessed to identify the specific sugar involved.
- Supernatant experiments were performed to rule out soluble factors mediating the response.
Main Results:
- Brief exposure to P. aeruginosa significantly enhanced PMN adherence and 3H-deoxyglucose uptake, indicating PMN activation.
- Maximal PMN stimulation occurred at a 10:1 PMN:bacteria ratio and 10 minutes of exposure.
- Bacterial treatments affecting surface ligand integrity abolished or reduced PMN-stimulatory capacity.
- Galactose, but not glucose, abrogated the PMN-stimulatory activity, suggesting a galactose-containing glycoprotein ligand.
- PMN stimulation was observed with P. maltophilia and P. pseudomallei, but not other tested Pseudomonas species.
Conclusions:
- Pseudomonas aeruginosa and related species activate PMNs through surface-associated factors, likely galactose-containing glycoproteins.
- These findings suggest that Pseudomonas species have a limited ability to evade PMN-mediated host defenses.
- This interaction may partially explain the opportunistic nature of these pathogens and the severity of infections when host PMN function is compromised.