Early diagnosis of tuberculous meningitis by an indirect ELISA protocol based on the detection of the antigen ESAT-6 in cerebrospinal fluid

BACKGROUND Early diagnosis of tuberculous meningitis (TBM) is still a challenge; the present study aimed to establish a method of detecting the antigen early secreted antigenic target 6 (ESAT-6) in cerebrospinal fluid (CSF) by an indirect enzyme-linked immunosorbance assay (ELISA) protocol and to study the value of detecting ESAT-6 in CSF in the early diagnosis of TBM. METHODS An indirect ELISA protocol was used, employing a monoclonal antibody (mAb) against ESAT-6, which was used to demonstrate ESAT-6 in the CSF from TBM patients and non-TBM controls. CSF was obtained from 100 patients: confirmed TBM, clinically diagnosed TBM, disease controls, and healthy controls (n = 10). Pure recombinant ESAT-6 (standard product) was used in serial dilutions to detect the absorbance and to establish a standard curve from the data; the concentration was on the X axis vs. absorbance on the Y axis, and the standard curve was used to interpolate the concentration of ESAT-6 in samples. RESULTS The indirect ELISA method provided 88 % sensitivity and 92 % specificity for the diagnosis of TBM using a mAb to ESAT-6. The mean concentration of ESAT-6 in TBM patients was significantly higher than that of the non-TBM groups. There was also a significant difference in the mean ESAT-6 expression between the confirmed TBM patients and the clinically diagnosed TBM patients (p < 0.01). CONCLUSIONS Detection of ESAT-6 in the CSF of TBM patients by indirect ELISA protocol gives a reliable early diagnosis and can be used to develop an immunodiagnostic assay with increased sensitivity and specificity.