Equine immunoglobulin F(ab')(2) fragments protect cats against feline calicivirus infection

Feline calicivirus (FCV) causes upper respiratory tract infections in felines and threatens the health of wild and domestic felines. Clinically, specific drugs to treat FCV have not yet been developed. Here, IgG was extracted from inactivated FCV-immunized horse sera. Equine F(ab')(2) fragments were obtained from pepsin-digested IgG and then purified by protein-G column chromatography. In our study, equine immunoglobulin F(ab')(2) fragments showed efficient neutralizing activity in vitro against FCV and had therapeutic and prophylactic effects in FCV-infected cats. The anti-FCV-specific F(ab')(2) fragment can significantly alleviate the clinical symptoms of FCV-infected cats and reduce the viral loads of the trachea, lung and spleen. These results indicate that the F(ab')(2) fragment prepared from inactivated FCV-immunized horses may be used as a prophylactic and therapeutic agent for diseases caused by FCV.