Expression of interleukin-10 and interleukin-12 in piglets experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV).

The expression of mRNA encoding interleukin-10 (IL-10) and IL-12 was studied, by the reverse transcription-polymerase chain reaction and by in-situ hybridization with a non-radioactive digoxigenin-labelled cDNA probe, in formalin-fixed, paraffin wax-embedded lung tissue from piglets inoculated intranasally with a Korean isolate (North American genotype) of porcine reproductive and respiratory syndrome virus (PRRSV). IL-12p35-positive cells were detected in the lung at 1 day post-inoculation (dpi), their number increasing at 5 dpi, and rapidly decreasing thereafter. In contrast, IL-10- and IL-12p40-positive cells were detected in the lung at 1 dpi, their number increasing at 3 dpi, and rapidly decreasing thereafter. Hybridization signals for IL-10, IL-12p35 and IL-12p40 were always associated with inflammation. Expression of these cytokines was minimal in non-lesional lung of PRRSV-infected piglets and in normal lung from control piglets. In-situ hybridization in serial sections of lung tissues indicated close co-localization of PRRSV and these cytokines in interstitial pneumonia. The results suggest that the expression of IL-10 and IL-12 plays a role in pulmonary defence mechanisms against PRRSV infection.