Immunohistochemical Detection of Virulence-associated Rhodococcus equi Antigens in Pulmonary and Intestinal Lesions in Horses

Two horses with Rhodococcus equi infection were examined post mortem by an immunohistochemical method (peroxidase–antiperoxidase; PAP) with a monoclonal antibody (Mab 10G5) to the 15–17 kDa antigen of R. equi. One of the horses was also examined bacteriologically, R. equi being isolated in culture. Immunolabelling with this Mab was marked and widespread. On the other hand, the immunohistochemical reactivity of infected macrophages with a polyclonal antibody specific for lysozyme was slight. Thus, Mab 10G5 would appear to be a useful diagnostic reagent in R. equi infection, with or without cultural confirmation.