Divergent Immune Responses to Minor Bovine Mastitis-Causing Pathogens

Area of Science:

• Veterinary Immunology
• Bovine Mastitis Pathogenesis
• Microbial-Host Interactions

Background:

• Non-aureus staphylococci (NASM) and lactic acid bacteria (LAB) are increasingly implicated in bovine mastitis.
• The specific mechanisms by which these bacteria interact with bovine immune cells remain incompletely understood.

Purpose of the Study:

• To investigate the differential responses of bovine neutrophils to NASM (Staphylococcus hominis, Staphylococcus chromogenes) and LAB (Weissella paramesenteroides).
• To elucidate the role of Toll-like receptors (TLRs) and downstream signaling pathways in neutrophil defense against these pathogens.

Main Methods:

• Bovine neutrophils were challenged with S. hominis, S. chromogenes, and W. paramesenteroides.
• Apoptosis, TLR expression (TLR2, TLR6), phagocytosis, intracellular reactive oxygen species (ROS) production, and gene expression (TLRs, apoptosis-related genes) were analyzed.

Main Results:

• Neutrophils showed minimal apoptosis with both NASM and LAB challenge.
• TLR2 expression was high post-challenge, but TLR6 expression was low for NASM.
• Neutrophil phagocytosis and killing were impaired against NASM, particularly S. chromogenes, compared to LAB.
• Intracellular ROS production was consistently high.
• S. chromogenes induced upregulation of TLRs, ROS, and both pro/anti-apoptotic genes, differing from W. paramesenteroides in specific apoptosis-related gene expression (CASP9, BCL2).

Conclusions:

• Staphylococcus chromogenes actively manipulates bovine neutrophil function, including phagocytosis and gene expression, to evade immune clearance.
• Lactic acid bacteria (Weissella paramesenteroides) have a less significant impact on neutrophil apoptosis compared to NASM.
• Differential TLR6 recognition and phagocytic capacity contribute to the varying efficacy of neutrophil responses against NASM and LAB.