Residence and recruitment of leucocytes to the equine lung after EHV-1 infection.

The research examines the behaviour and recruitment of white blood cells to the lungs of ponies following infection with equid herpesvirus-1 (EHV-1).

Methodology

• The study involved bronchoalveolar leucocytes (white blood cells located in the bronchial and alveolar areas of the lungs) from five susceptible ponies and two immune ponies.
• The ponies were infected with EHV-1 through a nebulised aerosol, an ideal method for ensuring the virus reaches the lungs.
• White blood cell counts and phenotypic analyses of lymphocytes – a specific type of white blood cell – were undertaken using differential staining and an indirect immunofluorescence assay.
• These analyses used specific monoclonal antibodies to identify and count subsets of lymphocytes, namely CD4, CD5, CD8 and B lymphocytes. In this context, the CD numbers refer to different types of immune cells, each playing a distinct role in the immune response.

Findings

• Significant changes in white blood cell counts and profiles were observed following EHV-1 infection.
• A transient neutrophilia – an overabundance of neutrophils, another type of white blood cells – developed on the second day post-infection, alongside a reduction in the numbers of macrophages, which are large white blood cells that consume foreign substances and cell debris.
• A significant decrease in the numbers of three types of lymphocytes (EqCD5+, EqCD4+ and EqCD8+) was also noted.
• Three weeks post infection (Day 21), a rise in EqCD8+ lymphocytes was observed. There was a corresponding decrease in the ratio of EqCD4+ to EqCD4+ lymphocytes and changes in B lymphocyte phenotypes.
• These findings show that the presence and kinds of white blood cells in the lung change dynamically following EHV-1 infection.

Conclusion

• The research concludes that following EHV-1 infection, leucocyte (or white blood cell) migration in the bronchoalveolar compartment of the lung is highly dynamic.
• This dynamic behavior of leucocytes may play an important role in the immunopathogenesis – how the immune response contributes to the progression of the disease – and recovery from the disease.