Submitted to: Clinical and Diagnostic Laboratory Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/1995
Publication Date: N/A
Citation: Interpretive Summary: Johne's disease is an economically important disease of cattle, sheep, and other ruminants. The organism that causes Johne's disease, Mycobacterium paratuberculosis, is difficult to study because it has special growth requirements and is extremely slow growing. Therefore, little is known about specific genes and proteins of M. paratuberculosis. In this study, we isolated and sequenced a gene that encodes a heat shock protein. Heat shock proteins are an important group of proteins to study and characterize because they may be involved in the disease process. We determined that the nucleic acid and amino acid sequence of the M. paratuberculosis protein is very similar to proteins found in other disease causing mycobacteria, such as M. tuberculosis, M. leprae, and M. avium. Blood from cattle infected with M. paratuberculosis did not consistently react with the protein. These results indicate that the protein probably will be of limited value for use in diagnostic tests for Johne's disease. However, the protein will be used for studies to determine the role of this protein in development of disease. It is important to more fully understand how M. paratuberculosis causes disease in the host so that improved diagnostic tests, vaccines, and methods for control of infection can be developed.
Technical Abstract: Mycobacterium paratuberculosis, the causative agent of Johne's disease in ruminants, has been implicated as a possible cause of Crohn's disease, an inflammatory bowel disease of unknown etiology. The mycobacterial 65K heat shock proteins (hsp-65K) are among the most extensively studied mycobacterial proteins. We isolated and sequenced the hsp-65K-encoding gene from our M. paratuberculosis PTB65K genomic library. The open reading frame (ORF) of the PTB65K gene was similar to the ORF for genes encoding hsp-65K of M. tuberculosis (89.6%), M. leprae (86.6%), and M. avium 18 (98.8%). The amino acid sequence of the PTB65K protein differed from the hsp-65K homologs of M. tuberculosis and M. leprae by 36 residues and from M. avium 18 by 8 residues. In immunoblot assays, sera from 3 of 10 clinical, 5 of 25 subclinical, and 0 of 10 normal cows reacted with the PTB65K protein. In addition, sera from two of two sheep and one of two goats with clinical Johne's disease reacted with the PTB65K protein. In humans, sera from 7 of 13 patients with Crohn's disease, 3 of 4 with tuberculosis, 5 of 6 with leprosy, 5 of 12 with noninflammatory bowel disease, and 0 of 4 with ulcerative colitis reacted with the recombinant PTB65K antigen. Results of this study indicate that the PTB65K protein will be of limited value for serodiagnosis of Johne's disease in animals. However, it may be useful to study the possible role of mycobacteria in some cases of Crohn's disease.