Immune response against equine gammaherpesvirus in Icelandic horses.

Horses are hosts to two types of gammaherpesviruses, equine herpes virus (EHV) 2 and 5. While EHV-2 is ubiquitous in adult horses, EHV-5 has been less frequently described. Due to strong serological cross-reactivity, EHV-2 and -5 cannot be discriminated in broad spectrum antibody tests and are thus commonly referred to as gamma-EHV. Total IgG and IgG subclass response against gamma-EHV were determined in serum from 41 healthy Icelandic horses, thereof 20 adults, 10 foals aged 10 months, and 11 foals aged 1-4 months. Additionally, in 10 of the adult horses, interferon (IFN)-gamma and interleukin (IL)-4 expression were measured by real-time PCR in white blood cells upon in vitro stimulation with EHV-2. With the exception of one orphan foal, all tested individuals were seropositive for gamma-EHV. All but one adult had high titer of EHV-specific IgG4/7 (IgGb) in combination with much lower titer of IgG1 (IgGa) and IgG3/5 (IgG(T)), indicating a stabilized response. IgG titer and subclasses in the foals showed considerably more variation, possibly dependant on maternal antibodies and/or recent infection. In all the 10 horses tested for cytokine expression, IFN-gamma production exceeds production of IL-4. These results indicate that equine gammaherpesvirus infection is characterized by an induction of IgG1, IgG4/7 and IgG3/5 with prevailing IgG4/7 and cytokine profile dominated by IFN-gamma. To our knowledge, this is the first report on the cytokine and IgG subclass response against gamma-EHV in horses.