Equine cell-mediated immune response to Rhodococcus (Corynebacterium) equi

Area of Science:

• Veterinary Immunology
• Equine Infectious Diseases

Background:

• Rhodococcus equi (R equi) causes significant respiratory disease in foals.
• Assessing cell-mediated immunity (CMI) is crucial for understanding equine immune responses to R equi.
• Existing methods for evaluating CMI in horses against R equi are limited.

Purpose of the Study:

• To develop and validate a lymphocyte blastogenic assay as an in vitro correlate of CMI to R equi in equines.
• To investigate the development of CMI following experimental R equi inoculation.
• To assess CMI responses in horses from herds with endemic R equi infections.

Main Methods:

• Development of a lymphocyte blastogenic assay using R equi heat and lysozyme extracts.
• Experimental inoculation of ponies with live R equi via subcutaneous, intranasal, and intratracheal routes.
• Performance of blastogenesis assays and delayed-type hypersensitivity tests on experimental and field-collected samples.

Main Results:

• Lymphocytes from experimentally inoculated ponies demonstrated a mitogenic response to R equi antigens post-inoculation.
• Non-inoculated control ponies showed no lymphocyte response to R equi antigens.
• Delayed-type hypersensitivity reactions were observed in all experimentally exposed ponies.
• Blastogenesis assays on horses from endemic herds revealed significant cell-mediated responses, but without clear correlation to clinical history.

Conclusions:

• The developed lymphocyte blastogenic assay is a viable tool for assessing CMI to R equi in equines.
• Cell-mediated immunity plays a role in the equine immune system's interaction with R equi.
• Further research is needed to correlate CMI responses with clinical outcomes in naturally infected herds.