Haemophilus somnus-induced interference with bovine neutrophil functions

Area of Science:

• Bovine immunology
• Bacterial pathogenesis
• Cellular immunology

Background:

• Haemophilus somnus is a significant pathogen in cattle.
• Bovine polymorphonuclear leukocytes (PMNs) are crucial immune cells for combating bacterial infections.
• Understanding bacterial interference with host immune function is vital for disease control.

Purpose of the Study:

• To investigate the in vitro effects of Haemophilus somnus on bovine PMN function.
• To identify bacterial components responsible for inhibiting PMN activity.

Main Methods:

• Incubation of bovine PMNs with live and heat-killed Haemophilus somnus cells, cell-free supernatant, and extracted bacterial fractions.
• Assays to measure PMN protein iodination and Staphylococcus aureus ingestion.
• Analysis of nitroblue tetrazolium (NBT) reduction by PMNs.

Main Results:

• Live, heat-killed whole cells, and supernatant fluid of Haemophilus somnus significantly inhibited PMN protein iodination and S. aureus ingestion.
• Washed, heat-killed cells did not inhibit these functions, suggesting soluble or surface-associated factors.
• No inhibition of NBT reduction was observed.
• The factor inhibiting S. aureus ingestion was heat-stable with a molecular weight >300,000 MW.
• The factor inhibiting protein iodination was <10,000 MW.

Conclusions:

• Haemophilus somnus produces factors that impair critical bovine PMN functions.
• These bacterial factors, particularly a high molecular weight surface component and a low molecular weight soluble factor, contribute to immune evasion.
• Further research into these factors could inform strategies to enhance bovine immune responses against H. somnus infections.