IL7 and viral infectious disease: PRRSV infection also impacted the mRNA expression of several cytokines in alveolar macrophages, including the up-regulation of TNFA, IL16, IL18, IL1A, IL10, IFNG and TGFB1, and the down-regulation of IL7, IL15, and TGFA1. The increased expression of TNFA and IL10 are consistent with the serum cytokine results reported by Liu et al. [7] and are likely due to the important regulatory roles of these cytokines in the early immune response to a viral infection [32, 33].