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Interaction of polymorphonuclear leukocytes with smooth and rough strains of Brucella abortus
Abstract:
The bactericidal activity of guinea pig and human polymorphonuclear leukocytes (PMNs) against a smooth-intermediate strain (45/0) and a rough strain (45/20) of Brucella abortus has been examined. After incubation for 120 min, guinea pig PMNs incubated with either the smooth strain 45/0 or the rough strain 45/20 exhibited no bactericidal activity against the former and caused only a 34% decrease in viability of the latter. Human PMNs were more bactericidal than guinea pig PMNs to both strains; however, the killing of strain 45/20 by human PMNs was less than that observed in control experiments with S. aureus strain 502A. Both strains of B. abortus readily associated with guinea pig and human PMNs, and the bacteria were apparently ingested without stimulation of the hexose monophosphate pathway. Lysates (10 micrograms/ml, pH 5.5), prepared from guinea pig or human granules, were not particularly toxic to either strain unless supplemented with H2O2 and a halide (I- or Cl-). An oxygen-dependent killing system appeared to be lethal against both strains of B. abortus, with I- being more active than Cl- in the presence of H2O2 and granule lysate. The data suggest that degranulation after ingestion of Brucella by phagocytes does not occur due to the lack of a proper stimulus or possibly the baccilli actively inhibit the degranulation process thereby protecting the microbe from killing systems normally effective against extracellular parasites.
Insights
Guinea pig and human polymorphonuclear leukocytes (PMNs) show limited bactericidal activity against Brucella abortus. Bacteria may inhibit phagocyte degranulation, evading immune defenses.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Polymorphonuclear leukocytes (PMNs) are crucial immune cells involved in phagocytosis and killing of bacteria.
- Brucella abortus is a facultative intracellular bacterium that causes brucellosis, a zoonotic disease.
- The interaction between PMNs and Brucella abortus is critical for controlling infection, but the mechanisms are not fully understood.
Purpose of the Study:
- To investigate the bactericidal activity of guinea pig and human PMNs against smooth and rough strains of Brucella abortus.
- To explore the role of the hexose monophosphate pathway and granule-derived antimicrobial systems in PMN-mediated killing of Brucella.
- To elucidate potential mechanisms by which Brucella abortus evades PMN-mediated killing.
Main Methods:
- Incubation of Brucella abortus strains (smooth 45/0 and rough 45/20) with guinea pig and human PMNs.
- Assessment of bacterial viability after PMN incubation.
- Analysis of hexose monophosphate pathway stimulation.
- Evaluation of the bactericidal activity of PMN granule lysates supplemented with H2O2 and halides (I- or Cl-).
Main Results:
- Guinea pig PMNs exhibited minimal bactericidal activity against both Brucella strains.
- Human PMNs showed greater bactericidal activity than guinea pig PMNs, but less than against Staphylococcus aureus.
- Both Brucella strains readily associated with and were ingested by PMNs without stimulating the hexose monophosphate pathway.
- PMN granule lysates required H2O2 and halide supplementation for significant bactericidal activity, with iodide being more effective than chloride.
- An oxygen-dependent killing system was lethal to Brucella, with iodide enhancing this effect.
Conclusions:
- PMN degranulation may not occur effectively after Brucella ingestion, potentially due to a lack of stimulus or active inhibition by the bacteria.
- Brucella abortus appears to evade PMN-mediated killing mechanisms, possibly by inhibiting degranulation.
- These findings highlight novel strategies employed by Brucella to survive within phagocytic cells, contributing to persistent infections.