Gram-positive bacteria-induced granulocytopenia and pulmonary leukostasis in rabbits

Area of Science:

• Immunology
• Microbiology
• Pathophysiology

Background:

• Pneumococci are known to cause granulocytopenia and pulmonary leukostasis, contributing to pneumococcal sepsis severity.
• The role of other gram-positive bacteria in inducing these phenomena remains less understood.

Purpose of the Study:

• To investigate whether other common gram-positive bacterial species can induce granulocytopenia and pulmonary leukostasis.
• To explore the mechanisms by which these bacteria interact with the host immune system.

Main Methods:

• Rabbits were challenged with nonviable preparations of Group A and B streptococci, Staphylococcus aureus, Bacillus cereus, and Clostridium perfringens.
• In vitro studies assessed complement consumption, granulocyte chemotaxis, and granulocyte adherence in rabbit serum incubated with these bacteria.
• The effects of infusing sonicate-exposed sera into recipient rabbits were evaluated.

Main Results:

• All five tested gram-positive species induced profound granulocytopenia (90% decrease) and pulmonary leukostasis in rabbits.
• Incubation of serum with these bacteria led to significant complement consumption (90%), increased granulocyte chemotaxis (204%), and augmented granulocyte adherence (45%).
• Infusion of sera exposed to bacterial sonicates induced granulocytopenia in recipient rabbits, indicating the presence of a neutropenia-inducing factor.

Conclusions:

• Several nonviable gram-positive species can activate the complement system, leading to C5a generation, enhanced granulocyte adherence, and a neutropenia-inducing factor.
• These complement-mediated alterations may contribute to granulocytopenia and pulmonary leukostasis.
• These phenomena likely play a significant role in the morbidity and mortality associated with gram-positive bacterial infections.