Determination of the cell tropism of serotype 1 feline infectious peritonitis virus using the spike affinity histochemistry in paraffin-embedded tissues

Abstract

Unlike for serotype II feline coronaviruses (FCoV II), the cellular receptor for serotype I FCoV (FCoV I), the most prevalent FCoV serotype, is unknown. To provide a platform for assessing the pattern by which FCoV I attaches to its host receptor(s), HEK293 cell lines that stably express the ectodomains of the spike (S) proteins derived from a FCoV I feline enteric coronavirus strain UU7 (FECV UU7) and a feline infectious peritonitis virus strain UU4 (FIPV UU4) were established. Using the recombinant S proteins as probes to perform S protein affinity histochemistry in paraffin-embedded tissues, although no tissue or enteric binding of FECV UU7 S protein was detected, it was found that by immunohistochemistry that the tissue distribution of FIPV UU4 S protein-bound cells correlated with that of FIPV antigen-positive cells and lesions associated with FIP and that the affinity binding of FIPV UU4 S protein on macrophages was not affected by enzymatic removal of host cell-surface sialic acid with neuraminidase. These findings suggest that a factor(s) other than sialic acid contribute(s) to the macrophage tropism of FIPV strain UU4. This approach allowed obtaining more information about both virus–host cell interactions and the biological characteristics of the unidentified cellular receptor for FCoV I.