A proteomic approach to investigate immunity against R. Equi in foals.

Rhodococcus equi is a soil organism distributed worldwide. The major infection caused by R.equi is a granulomatous pneumonia often fatal in foals aged between one and six months (Cornish and Washington, 1999). While R. equi is present in most horse breeding, virulence in foals is highly associated to breeding management, the immune response of the foal and the espression of the VAP gene (virulence associated protein) by the microorganism. R. equi has emerged as an important human pulmonary pathogen, particularly in HIV-infected and immunocompromised patients (Drancourt et al., 1992; Emmons et al., 1991). The major feature of the pathogenesis of R. equi infections is the ability of the organism to survive and replicate inside alveolar macrophages (Hietala and Ardans, 1987; Zink et al., 1987). Experimental data suggest that R. equi is capable of inhibiting the oxidative bactericidal functions of polymorphonuclear cells. Electron microscopy of R. equi in equine macrophages show the capability of the organism to survive by interfering with phagosome-lysosome fusion. The exact mechanism of infection and how and why this micro-organism mainly affects newborn foals is still unknown. These questions can only be answered only by a better understanding of the biology and epidemiology of R. equi infection (Taouji et al., 2002). Proteomics, which allows analysis of the entire protein complement of a genome, (Wasinger et al., 1995) could be useful to elucidate the biology of the microorganism and to detect the diagnostic and prognostic markers involved in the pathogenesis of infection. The aim of this work was to compare two dimensional electrophoresis (the starting point of a typical proteome project) of equine serum to evaluate protein differences due to the different immune responses (active and passive) against R. equi in foals. The identification of proteins is performed by matching (overlap with a published database of equine serum) and mass spectrometry MALDI-TOF.