Avaliação da imunogenicidade de antígenos recombinantes do mycobacterium tuberculosis para desenvolvimento de teste de diagnóstico sorológico para a tuberculose

Abstract

Introduction: Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb). According to the WHO, one-third of the world population is infected with Mtb and about 5% of these individuals will develop active disease. Mtb can affect various organs, having the lungs as its main target (pulmonary TB). TB diagnosis can be confirmed by the presence of alcool acid resistant bacilli in biological samples. However, this technique has a variable sensitivity (35% to 85%) therefore, it is necessary the development of new laboratory methods. The first objective of this work was to evaluate the immunogenicity and antigenicity of the recombinant protein GroES from Mtb using an indirect ELISA in TB patients and their household contacts; the second objective was evaluate the performance of a recombinant fusion protein expressing immunodominant epitopes previously identified as immunogenic and antigenic: Antigen 85C, MPT-51 and Hsp-X in the discrimination of patients with active TB from healthy controls from endemic areas. Methods: This is a transversal study. In the first study it was tested the recombinant GroES antigen in an indirect ELISA and the study population was constituted of 45 patients with active TB and 172 healthy household contacts (HHC). The second study tested a recombinant fusion protein in an indirect ELISA and the study population was, composed by 35 patients with active TB, and 39 healthy control subjects (HC). All individuals who agreed to participate underwent tuberculin skin test (TST) and blood samples were withdrawn to obtain plasma and serum. We performed an indirect ELISA for IgG and IgM specific to GroES and the fusion protein. Results and conclusions: The results showed that in the IgM-ELISA specific for rGroES, the HHC, TST negative individuals, had antibody levels (0.233 ± 0.142) higher than active TB patients (0.193±0.140;p=0.0497). No differences were observed between active TB and HHC, TST positive for IgM specific to rGroEs. For the IgG-ELISA specific for rGroES, individuals with active TB had higher levels (0.203±0.214) when compared to HHC-TST negative (0.121±0.145; p=0.0168). For the IgG-ELISA-rGroES, using a cut-off of 0.052, the sensitivity was 78.38% (95% CI: 61.8 to 90.2%), and the specificity was 31.76% (95% CI: 22.1 to 42.8%). Individuals with active TB had IgG-rGroES (0.203±0.214) similar to the HHC, TST+ (0.167±0.181). In conclusion, the rGroES an antigen is immunogenic and antigenic, it was recognized by the humoral immune response of individuals with active and latent TB. The results for the ELISA specific for the fusion protein showed for IgG, that patients with active TB had higher antibody levels (0.407±0.141), than healthy controls (0.167±0.072; p<0.0001). The cutoff of 0.179 allowed a sensitivity of 100% (95% CI: 89.72-100%); and the specificity was 71.4% (95% CI: 53.70-85.36%). ELISA for specific IgM to fusion protein, showed that individuals with active TB presented higher levels (0.305±0.09), than the healthy controls (0.212±0.057; p<0.0001). In this case, using a cutoff of 0.226, the sensitivity was 80.0% (95% CI: 63.06-91.56%), and the specificity was 61.54% (95% CI: 44.62-76.64%). We conclude that the indirect ELISA using the fusion protein presented the best performance and can be improved in order to prepare a kit for the diagnosis of TB.