Kinetics of the expression of CD163 and CD107a in the lung and tonsil of pigs after infection with PRRSV-1 strains of different virulence

The emergence of virulent strains of porcine reproductive and respiratory syndrome virus (PRRSV), causing atypical and severe outbreaks, has been notified worldwide. This study assesses the expression, distribution and kinetics of PRRSV N-protein, CD163 and CD107a in the lung and tonsil from experimentally-infected piglets with three different PRRSV-1 strains: a virulent PRRSV-1 subtype 3 strain (SU1-bel) and two low-virulent subtype 1 strains, Lelystad virus (LV) and 215–06. SU1-bel replicated more efficiently in the lungs and tonsils. The number of CD163⁺ cells decreased in both tissues from all infected groups at 7 dpi, followed by an increase at the end of the study, highlighting a negative correlation with the number of N-protein⁺-infected cells. A significant increase in CD107a was observed in all infected groups at 35 dpi but no differences were observed among them. Whereas the initial decrease of CD163⁺ cells appears to be associated to virus replication and cell death, the later recovery of the CD163⁺ population may be due to either the induction of CD163 in immature cells, the recruitment of CD163⁺ cells in the area of infection, or both. These results highlight the ability of macrophage subpopulations in infected animals to recover and restore their potential biological functions at one-month post-infection, with the greatest improvement observed in SU1-bel-infected animals.