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 γ-EHV. Total IgG and IgG subclass response against γ-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)-γ 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 γ-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-γ 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-γ. To our knowledge, this is the first report on the cytokine and IgG subclass response against γ-EHV in horses.