Humoral Antibody Response to the Antigens of Virulent Rhodococcus equi in Foals

Abstract

The antibody response of foals to the antigens of virulent Rhodococcus equi was studied on two horse-breeding farms contaminated with R. equi using Western immunoblotting, and the results were compared with the antibody titers measured by ELISA. Virulent R. equi ATCC 33701 was used as an antigen for these immunoassays. Sera were collected five times from 19 foals on the two farms at regular intervals. ELISA titers o f these sera increased within 60 days after birth, and then gradually decreased to adult levels. Antibody response to the 15- to 17-kDa antigens was detected in accordance with the increase in ELISA titers in every foal. Some of the foals with clinical signs of respiratory tract infection showed a significant increase in ELISA titers. On these farms, virulent R. equi was isolated from their environmental soil. These results suggest that the foals studied were naturally exposed to virulent R. equi, and that humoral response to the 15- to 17-kDa antigens developed in accordance with age during the first 3 months of life