L5P a specific antigen suitable to detect mycobacterium avium spp. paratuberculosis infection by cell mediated immune response

Abstract

International audienceContext: The livestock management needs an early diagnostic test to prevent dramatic rise of Mycobacterium avium spp paratuberculosis (Map) infection in cattle. Current serology based diagnostic tests available, detect animals in later stages when they are shedding huge amount of bacillus. Cell mediated immune (CMI) responses that can be detected by Interferon Gamma Release Assays, appear before or combined with antibody responses. Therefore, diagnostic tools based on IGRA could help to identify recently infected animals in order to prevent disease transmission. The sensitivity and specificity of these tests need to define Map-specific T-cell antigens. Map produces a specific cell-wall lipopentapeptide called L5P or LP-01. L5P is suitable to detect Map-infected animals by serodiagnostic. Moreover, L5P can be synthetized chemically at high purity, large scale, and low cost. Objectives: The purpose of this work was to assess the potential of L5P to detect Map-specific cell mediated immune responses to develop an IGRA test. Methods: A panel of 36 cows were selected from two naturally infected herds where clinical paratuberculosis had occurred. We performed 1) serology with the commercial IDEXX diagnostic test and a house-made test using L5P antigen 2) IGRA with Purified Protein Derivative avian (PPD-A) or synthetic L5P antigen 3) microbiological analyses including isolation and identification of bacillus from faeces. Results: In this study 47.2 % of cows were scored positive by the commercial IDEXX diagnostic test but only 22% developed anti-L5P antibodies. PPD-A induced CMI responses in 97 % of cows while 22.2% animals were L5P responders. Map was isolated in 25.7% of animals. We provide, for the first time, evidence that Map-specific L5P is a suitable antigen for serologic and IGRA diagnosis. Perspectives: We will now carry out a longitudinal study to investigate the potential of L5P-based IGRA to predict clinical outcome of Map-infected 18-24 months cattle