Effect of porcine respiratory coronavirus infection on lipopolysaccharide recognition proteins and haptoglobin levels in the lungs

Porcine respiratory coronavirus (PRCV) potentiates respiratory disease and proinflammatory cytokine production in the lungs upon intratracheal inoculation with lipopolysaccharide (LPS) at 1 day of infection. This study aimed to quantify LPS-binding protein (LBP), CD14 and haptoglobin in the lungs throughout a PRCV infection. LBP and CD14 recognize LPS and enhance its endotoxic activity, whereas haptoglobin dampens it. Gnotobiotic pigs were inoculated intratracheally with PRCV (n = 34) or saline (n = 5) and euthanized 1–15 days post inoculation (DPI). Virus was detected in the lungs from 1 to 9 DPI. Cell-associated CD14 in lung tissue increased up to 15 times throughout the infection, due to an increase in highly CD14+ monocyte-macrophages from 1 to 12 DPI and CD14+ type 2 pneumocytes from 7 to 9 DPI. LBP and soluble CD14 levels in bronchoalveolar lavage fluids were elevated from 1–12 DPI, with up to 35- and 4-fold increases, respectively. Haptoglobin levels increased significantly (×4.5) at 7 DPI. In addition, we found that PRCV could sensitize the lungs to LPS throughout the infection, but the response to LPS appeared less enhanced at the end of infection (7 DPI). The marked increases in LBP, CD14 and haptoglobin were not correlated with the extent of the LPS response.