Immunohistochemical Detection of Virulence-associated Antigens of Rhodococcus equi in Pulmonary Lesions of Foals

Abstract

Rhodococcus equi was isolated from the lungs of six foals with bronchopneumonia. All isolates expressed 15-17-kd antigens by immunoblot analysis and contained a virulence-associated plasmid of 85 or 90 kb. Immunohistochemically, R. equi from all pulmonary lesions showed the expression of 15-17-kd antigens mainly in the phagocytic cells. The specific monoclonal antibody to 15-17-kd antigens of R. equi (MAb 10G5) may be an aid in the diagnosis of R. equi-induced pneumonia.

The pathological findings of Rhodococcus equi infection and its diagnosis with immunoperoxidase technique in foals

“…In this study, presence of macrophages, some of them were bacteria laden, within the lesions could be explained by role of these cells as the main defender against agents that are inhaled as previously reported (5,8,13,24 ).…”

“…R. equi has been detected by immunohistochemical methods, using polyclonal and monoclonal antibodies in formalin-fixed and parafin-embedded sections. R. equi antigens were demonstrated with immunoperoxidase technique usually in cytoplasm of macrophages and rarely in cytoplasm neutrophils and giant cells at lung and mediastinal lymph node sections (8,13,14,20,21,26). In the present study the R. equi antigens were located in the center of suppurative inflammation, in the bronchiole lumina, and in the cytoplasm of macrophages and rarely neutrophils.…”

“…Gram and ZN stains can be regarded only as diagnostic aids. But immunohistochemical tests which are highly sensitive and specific, detect intracellular and extracellular antigen (13). The immunohistechemical method is relatively inexpensive and, unlike PCR, does not require special laboratories or specilalist personel.…”

Expression of Virulence‐Associated Antigens of Rhodococcus equi Is Regulated by Temperature and pH

“…The 15-to 17-kDa antigens are expressed by virulent R. equi growing in vivo. Naturally infected foal sera reacted strongly with the virulence-associated antigens by immunoblotting (20,21), suggesting the antigens are recognized by infected hosts, and we directly demonstrated the expression of the antigens in phagocytic cells from pulmonary lesions of naturally infected foals using monoclonal antibodies (9). These virulence-associated antigens, which are induced by these signals, might be involved in the process of pathogenesis of R. equi infection in foals and humans.…”

“…The virulence-associated antigens are synthesized in vitro by virulent R. equi at temperatures similar to those of the mammalian body and at pH values similar to those in macrophage phagolysosomes or abscesses. R. equi acts as a facultative intracellular bacterium which survives within macrophages and eventually destroys them (9,12,22). Low pH is probably an important signal in the intracellular environment, and stress proteins produced by intracellular bacteria have been investigated for their protective role against host defense mechanisms (2, 5, 11).…”