A comparison of three avidin-biotin complex immunoenzyme systems for detection of African swine fever virus antigen in paraffin-embedded tissues

Foreign Animal Disease Diagnostic Laboratory, National Veterinary Services Laboratories, APHIS, USDA, Greenport, NY 11944, USA. The sensitivity and specificity of 3 avidin-biotin complex (ABC) immunostaining systems were compared on paraffin-embedded tissues from African swine fever virus (ASFV)-infected pigs. Results were also compared with immunofluorescent detection on cryosections of the same tissue for optimal detection of ASFV antigen. The ABC-alkaline phosphatase (ABC-AP) and ABC-peroxidase (ABC-PO) systems were at least as sensitive as direct fluorescent antibody (FA) and 10-fold more sensitive than the ABC-glucose oxidase system. Three ABC-AP and 2 ABC-PO chromagens with different counterstains were compared. In addition, 2 fixatives, 2 biotinylation procedures, 7 endogenous peroxidase blocking regimes, 6 tissue adhesives, and 3 mounting media were compared. The ABC-AP system with a red chromagen and hematoxylin counterstaining was preferred and most closely approximated routinely stained pathologic sections. Fixation in paraformalde-hydelysine-periodate fixative preserved ASFV antigen for research studies for at least 3 years. Formalin-fixed tissues retained some staining for up to 10 years.