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

This study characterised bronchoalveolar leucocytes collected by lavage from five susceptible and two immune ponies before and after nebulised aerosol infection with equid herpesvirus-1 (EHV-1). Leucocyte counts and lymphocyte phenotypic analyses were performed using either differential staining or an indirect immunofluorescence assay with monoclonal antibodies specific for equine (Eq) CD4, CD5, CD8 and B lymphocytes. After EHV-1 infection, significant changes developed: a transient neutrophilia occurred on Day 2, coincident with a reduction in macrophage numbers and an EqCD5+, EqCD4+ and EqCD8+ lymphopaenia. On Day 21, a significant rise in EqCD8+ lymphocytes with an associated fall in the EqCD4+: EqCD8+ ratio and fluctuations in B lymphocyte phenotypes were observed. This study shows that following EHV-1 infection, the bronchoalveolar compartment is subject to dynamic leucocyte migration which may have an important role in immunopathogenesis and recovery from disease.