A study concerning the genome-wide transcriptional response of primary alveolar macrophages (PAMs) following infection with the Lelystad PRRSV strain (European type, EU PRRSV) reported that the expression of beta interferon 1 (IFN-β1) was strongly up-regulated while expression of IL-10 and TNF-α was up-regulated slightly [8]. Here, TNF is linked to infection.