Evaluation of the Dual Antiviral and Immunomodulatory Effects of Phallus indusiatus in a Feline Infectious Peritonitis Model Using PBMCs

Feline infectious peritonitis (FIP) is a progressive and often fatal disease caused by a virulent biotype of feline coronavirus (FCoV). Although antiviral treatments are now available, relapse and resistance remain ongoing concerns. This study investigates the therapeutic potential of <i>P. indusiatus</i>, a medicinal mushroom, for its antiviral and anti-inflammatory activities against FIP. The main protease (FIPV M^pro) of feline infectious peritonitis virus (FIPV) was recombinantly expressed and purified to facilitate enzyme inhibition screening. <i>P. indusiatus</i> exhibited the strongest FIPV M^pro inhibitory activity among the 17 mushroom extracts tested (69.2%), showing a notable level of inhibition relative to standard antiviral agents such as lopinavir and ritonavir. To assess its anti-inflammatory potential, PBMCs derived from healthy cats and FIP-associated effusions (FIP fluid) were cultured and stimulated with LPS to induce inflammation. In healthy PBMCs, <i>P. indusiatus</i> significantly reduced nitrite levels, with effects similar to dexamethasone. However, PBMCs from FIP fluid, already in an activated state, showed no additional response. Notably, this study is the first to successfully isolate and culture PBMCs from FIP fluid, providing a new platform for future immunological research. These findings suggest that <i>P. indusiatus</i> possesses both antiviral and anti-inflammatory properties, positioning it as a potential dual-action therapeutic candidate for FIP. Further investigation into cytokine signaling pathways is warranted to clarify its mechanisms of action and advance future therapeutic development.