Antigenicity of envelope protein complexes of Mycobacterium avium subsp. paratuberculosis and insights into T cell responses of infected animals

Abstract

Paratuberculosis is a disease caused by Mycobacterium avium subsp. paratuberculosis (MAP). This is a chronic enteric disease of ruminant animals with clinical signs taking from 2 to 5 years for manifestation. Current diagnostic tests are effective in identifying animals in later stages of infection; however, sensitivity among animals in the early stages of infection is low. In addition, currently available vaccines in the US fail to prevent infection of animals. Transitions in host immunity to MAP leading to clinical disease are poorly understood and their comprehension could lead to more targeted approaches for vaccine and diagnostic development. The objective of the first study was to identify protein complexes in the envelope of MAP to gain insight into pathogenic mechanisms as well as to identify antigenic proteins. Seven protein complexes were identified in the envelope of MAP and these complexes were fragmented into individual proteins with potential as diagnostic and vaccine targets. The second objective in this thesis was to study two crucial molecules in T cell signaling investigated in cows with subclinical and clinical disease. ZAP-70 (zeta-chain associated protein of 70 kDa) is involved in proximal T cell receptor signaling and its activation is necessary for T cell effector function. The second molecule studied was CTLA-4 (cytotoxic T-lymphocyte antigen-4), regarded as one of the major negative regulators of T cell function. All MAP infected animals demonstrated a significant reduction in expression of ZAP-70 among CD4+ T cells whereas only animals of subclinical status had a significant upregulation of CTLA-4 in the CD4+ T cell population. Both studies