Horses are usually infected during the first months of life by several equine herpesviruses, such as EHV-1, EHV-4 or EHV-2. The persistence of these respiratory viruses through establishment of latency, often characterised by an absence of clinical signs, represents a real risk to the horse population. A better understanding of the immune response after EHV infection is necessary to improve our methods of prevention and decrease the risk of transmission. The objectives of this study were 1/ to characterise the cytokine gene expression profile of PBMC after in vitro EHV infection (EHV-1, EHV-4 and EHV-2) and 2/ To determine the efficacy of the inactivated Parapoxvirus ovis (iPPVO), a known immunomodulator in horses, against these three viruses.PBMC isolated from 3 horses were infected in vitro with EHV-1, EHV-4 or EHV-2, in the presence or absence of iPPVO. Cytokine expression profiles (IFN-alpha, IFN-beta, IFN-gamma, TNF-alpha, IL-6, IL-10) were measured by qRT-PCR.In vitro culture of PBMC after EHV-1, EHV-4 or EHV-2 infection in the presence of iPPVO induced a significant increase of IFN-alpha, IFN-beta and IFN-gamma gene expression. Moreover, EHV-2 induced a significant increase of IL-1beta, IL-6 and TNF-alpha mRNA. The presence of iPPVO induced an earlier and stronger expression of IFN-alpha, IFN-beta and IFN-gamma during EHV infections. The presence of iPPVO also reduced the inflammatory response induced by EHV-2. In conclusion, this study suggests that the presence of iPPVO potentiates the development of the immune response during EHV infection in vitro.