Vol. 59, No. 7
Identification of B- and T-Cell Epitopes within the MTP40 Protein of Mycobacterium tuberculosis and Their Correlation with the Disease Courset
JUAN C. FALLA, CARLOS A. PARRA,* MARCELA MENDOZA, LINA C. FRANCO, FANNY GUZMAN, JAVIER FORERO, OSCAR OROZCO, AND MANUEL E. PATARROYO Instituto deInmunologia, Hospital San Juan de Dios, Carrera 10 Calle 1, Bogota, Colombia
Received 25 March 1991/Accepted 11 April 1991
Synthetic peptides derived from the amino acid sequence of MTP40, a recently characterized Mycobacterium tuberculosis protein, were tested by two different immunological assays in 91 individuals. For the purposes of this study, the population was distributed in four groups: activetuberculosis (TBC) patients with elevated bacillus loads (BK+), active TBC patients with low bacillus loads (BK-), healthy individuals living in the same household with tuberculous patients (HH), and normal individuals, who had presumably never been in contact with the bacilli (control). We found that T cells of individuals belonging to the HH group showed the highest and most frequent recognitionof these peptides in a T-cell proliferation assay, while their antibodies showed the lowest recognition of these peptides when tested by enzyme-linked immunosorbent assay. In contrast, TBC patients revealed an inverse pattern of immune response. Interestingly, one of these peptides (P7) was recognized by T cells of 64% of the HH individuals and by 4.5% of normal donors. Another peptide (P4) wasrecognized by 55% of sera from BK+ patients and by 5.5% of normal donors. The results presented here indicate the existence of T- and B-cell epitopes within the MTP40 protein. Given the particular recognition pattern of this protein, added to the fact that it appears to be a species-specific antigen of M. tuberculosis, a detailed study of the immune response to it may be useful in the design ofmore accurate diagnostic tests and an improved vaccine against human TBC. Tuberculosis is a chronic infectious disease caused, in the human host, by Mycobacterium tuberculosis, M. bovis, and M. africanum. The complex antigenic composition of mycobacteria and the presence of cross-reactive epitopes throughout the group (38) has made it difficult to develop efficient immunological methods fordiagnosis. Although the tuberculin test has been helpful in roughly defining groups of tuberculous patients (42), more sensitive and specific assays that provide reliable diagnostic results are needed. On the other hand, the limited success of M. bovis BCG vaccination in developing countries has brought into doubt its effectiveness in controlling the disease (34, 43). For these reasons, new approaches arerequired to precisely identify epitopes within immunologically important antigens which might be useful for the diagnosis of and protection from the disease
The development of serological methods for diagnosing tuberculosis has been the object of study of several groups (12). Tests based on the enzyme-linked immunosorbent assay (ELISA) and radioimmunoassays with purified protein derivative (PPD)have been developed, but the results have been disappointing (18, 39). Daniel and coworkers have performed ELISAs with antigen 5 (8, 33), which, although a well-characterized protein, is still not as specific as required for these purposes. Although the use of antibodies in diagnosis has been attempted (8), little is known concerning their role in protection against tuberculosis. While manyreports indicate that they are not important components mediating protection (7, 10), others have proposed that an antibody-mediated
t This article is dedicated to the memory of Juan C. Falla.
mechanism could play an important role in protection during the early stages of the bacillary infection (9). Several B-cell epitopes have been recently identified...