Development and application of a porcine specific ELISA for the quantification of soluble CD163

The cellular marker CD163 is a type 1 transmembrane scavenger protein found either on the surface of antigen-presenting cells or in a soluble form (sCD163), released in response to inflammation. Despite an obligatory role in porcine reproductive and respiratory virus (PRRSV) infection, information on sCD163 as a biomarker of disease outcome in swine remains limited. In the present study, we developed a sandwich ELISA using an anti-bovine CD163 antibody, LND68A, in conjunction with the porcine specific 2A10/11 antibody. The ELISA demonstrated that CD163 shedding from porcine alveolar macrophages increased following in vitro exposure to lipopolysaccharide or PRRSV-2 strain NVSL 97-7895. Evaluation of serum sCD163 in healthy feeder pigs identified a significant age effect with concentration rising after birth to a peak at day 19 (P < 0.05) followed by a sharp decline to a minimal level of detection at 9 weeks of age (P < 0.05). Healthy sows showed substantial variation but no significant change in average concentration between early and late lactation. The serum concentration of sCD163 from pigs with homozygous gene edits disrupting translation of the CD163 protein was below the threshold of detection. However, when reformatted as a competitive ELISA the assay identified an interfering substance consistent with the release of a truncated form of the CD163 protein in sera from gene edited animals. With sCD163 shown to be both dynamic and responsive, the described ELISA represents a novel tool for investigation of this molecule as a potential biomarker of disease response in the pig.