Avaliação da concentração de Interferon-gama em pacientes com Tuberculose pulmonar e contatos diretos, por Quantiferon TB Gold (In tube method)

Abstract

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis complex species, which infect the exposed individuals, initiate an immune response with production of several cytokines, among them interferon-gamma (IFN-gamma), which is crucial for activation of cellular immune response against TB bacillus. This cytokine has been extensively studied as a possible biomarker for diagnosis of TB. In this work, we analyzed the levels of IFN-gamma in response to in vitro stimulation with ESAT-6, CFP10 and TB7.7, by QuantiFERON ®-TB Gold (In-tube method) (QTF-IT) in 155 participants: 47 patients confirmed pulmonary TB (patient group), 49 direct contacts (group contact), and 59 individuals without history or contact with TB (control group). The levels of IFN-gamma were different among the groups (p=0.0001); the highest level was observed in the patients group (median=1.43 IU/mL). In contacts group, 20/49 (40.8%) subjects were positive for the QTF-IT (median = 0.26 IU / mL), and among these positive contacts 14/20 (70.0%) exhibited high levels of IFN-gamma, (≥ 1.05 IU/mL). The performance testing of TB patients versus controls, resulted in 80.9% sensitivity (95% CI = 69.6% to 92.1%) and 93.2% specificity (95% CI = 86.8 % to 99.6%), but when the results of contacts and control group were combined, the specificity decreased to 77.8% (95% CI = 69.9% to 85.6%). Thus, according to our data, there is a distinctive profile of IFN-gamma, with higher levels in the patients group. The QTF-IT positive in contacts, especially those with high levels of IFN-gamma, should be monitored, especially those with high levels of IFN-gamma. This result may be a risk factor for developing TB disease. In addition, the QTF-IT, properly executed, can be useful in endemic areas for the diagnosis of latent and active TB (infection) when evaluated with other routine tests.