Equine herpesvirus-1 infection induces IFN-γ production by equine T lymphocyte subsets

A commercial bovine IFN-γ-specific monoclonal antibody was used to measure antigen-specific IFN-γ production by equine lymphocytes. Paired PBMC samples were collected from six ponies prior to and 10 days after challenge infection with equine herpesvirus-1 (EHV-1). Each sample was stimulated in vitro with EHV-1, virus-free medium, or PMA and ionomycin, and labelled with monoclonal antibodies specific for various equine lymphocyte subset markers. Following fixation, intracellular IFN-γ was detected using a FITC-conjugated bovine IFN-γ-specific monoclonal antibody. ro restimulation of PBMC with EHV-1 induced IFN-γ production by a significantly higher percentage of total (CD5+) T lymphocytes, and CD4+ and CD8+ T lymphocyte subsets among post-EHV-1 infection PBMC samples compared to pre-infection samples. This response was associated with an increase in virus-specific CTL activity, a critical immune effector for the control of EHV-1 infection and disease. No significant increase in IFN-γ production by B lymphocytes was observed. These data demonstrate that EHV-1 challenge infection of ponies results in increased production of IFN-γ by virus-specific T lymphocytes, and that this response can be quantitated using flow cytometry.