Cerebrospinal T-cell responses aid in the diagnosis of tuberculous meningitis in a human immunodeficiency virus- and tuberculosis-endemic population

Abstract

Rationale: Current tools for the rapid diagnosis of tuberculous meningitis (TBM) are suboptimal. We evaluated the clinical utility of a quantitative RD-1 IFN-gamma T-cell enzyme-linked immunospot (ELISPOT) assay (T-SPOT.TB), using cerebrospinal fluid cells for the rapid immunodiagnosis of TBM.

Objectives: To evaluate the diagnostic utility of the RD1 antigen- specific ELISPOT assay for the diagnosis of tuberculous meningitis.

Methods: The ELISPOT assay was evaluated in 150 patients with suspected TBM who were categorized as definite-TBM, probable-TBM, and non-TBM. Culture or polymerase chain reaction positivity for Mycobacerium tuberculosis served as the reference standard. To determine the diagnostic value of the ELISPOT assay, a clinical prediction rule was derived from baseline clinical and laboratory parameters using a multivariable regression model.

Measurements and main results: A total of 140 patients (81% HIV-infected; median CD4 count, 160 cells/mm(3)) were included in the final analysis. When comparing the definite-TBM (n = 38) and non-TBM groups (n = 48), the ELISPOT assay (cut point of > or =228 spot-forming cells per 1 million mononuclear cells) was a useful rule-in test: sensitivity 58% (95% confidence interval [CI], 41-74); specificity 94% (95% CI, 83-99). However, ELISPOT outcomes improved when other rapid tests were concurrently used to exclude bacterial (Gram stain) and cryptococcal meningitis (latex-agglutination test) within the non-TBM group. Using this approach, the ELISPOT assay (cut point of > or =46 spot-forming cells) was an excellent rule-in test: sensitivity 82% (95% CI, 66-92); specificity 100% (95% CI, 78-100); positive predictive value, 100% (95% CI, 89-100); negative predictive value, 68% (95% CI, 45-86); area under the curve, 0.90. The ELISPOT assay had incremental diagnostic value compared with the clinical prediction rule.

Conclusions: The RD-1 ELISPOT assay, using cerebrospinal fluid mononuclear cells and in conjunction with other rapid confirmatory tests (Gram stain and cryptococcal latex-agglutination test), is an accurate rapid rule-in test for TBM in a TB and HIV endemic setting.

Figure 1.

Summary flow chart of patients recruited, investigations performed, and patient categorization. PCR = polymerase chain reaction; VDRL = venereal disease research laboratory.

Figure 2.

RD1 antigen–specific responses to early secreted antigenic target 6 and culture filtrate protein 10 using cerebrospinal fluid mononuclear cells comparing definite-, probable-, and non-tuberculous meningitis (TBM) groups. (A) Definite-TBM compared with the unselected non-TBM group and (B) the corresponding receiver operating characteristic (ROC) curve. (C) Responses when the non-TBM group was stratified by rapid test results (gram positive or cryptococcal antigen latex agglutination test [CLAT] positive vs. gram negative and CLAT negative) and (D) the corresponding ROC curve. (C) For clarity, the probable-TBM group is not shown.

Figure 3.

IFN-γ responses to purified protein derivative, using cerebrospinal fluid (CSF) mononuclear cells, comparing the definite-, probable-, and unselected non-tuberculous meningitis (TBM) groups. (A) Definite-TBM compared with the unselected non-TBM group (cut-point 46 spot-forming cells per 10⁶ CSF mononuclear cells) and (B) the corresponding receiver operating characteristic (ROC) curve. (C) Responses when the non-TBM group was stratified by rapid test results (gram positive or cryptococcal antigen latex agglutination test [CLAT] positive versus gram negative and CLAT negative) and (D) the corresponding ROC curve.