Diagnosis of central nervous system tuberculosis by T-cell-based assays on peripheral blood and cerebrospinal fluid mononuclear cells

Abstract

In active tuberculosis (TB), Mycobacterium tuberculosis-specific T cells are compartmentalized more to the site of infection than to the circulating blood. Therefore, an M. tuberculosis-specific enzyme-linked immunospot (ELISPOT) assay with samples from the site of infection may permit a more sensitive or specific diagnosis of active central nervous system (CNS) TB than that achieved by the assay with blood alone. Therefore, we prospectively evaluated the usefulness of circulating and compartmentalized mononuclear cell (MC; i.e., peripheral blood mononuclear cell [PBMC] and cerebrospinal fluid [CSF] MC)-based ELISPOT assays (i.e., the T-SPOT.TB test) for the diagnosis of active TB in patients with suspected CNS TB. The clinical categories of CNS TB were classified as described previously (G. E. Thwaites, T. T. Chau, K. Stepniewska, N. H. Phu, L. V. Chuong, D. X. Sinh, N. J. White, C. M. Parry, and J. J. Farrar, Lancet 360:1287-1292, 2002). Thirty-seven patients with suspected CNS TB were enrolled over a 12-month period. Of these, 31 (84%) showed clinical manifestations of suspected TB meningitis and 6 (16%) gave indications of intracranial tuberculoma with disseminated TB. The final clinical categories of the 37 patients with suspected CNS TB were as follows: 12 (32%) were classified as having CNS TB (7 with confirmed TB, 3 with probable TB, and 2 with possible TB) and 25 (68%) were classified as not having active TB. The sensitivity and specificity of the PBMC ELISPOT assay were 91% (95% confidence interval [CI], 59% to 100%) and 63% (95% CI, 41% to 81%), respectively. By comparison, the sensitivity and specificity of the CSF MC ELISPOT assay were 75% (95% CI, 19% to 99%) and 75% (95% CI, 43% to 95%), respectively. When the ratio of the CSF MC ELISPOT assay results to the PBMC ELISPOT results was 2 or more, the sensitivity and specificity were 50% (95% CI, 7% to 93%) and 100% (95% CI, 74% to 100%), respectively. The ELISPOT assay with PBMCs and CSF MCs is a useful adjunct to the current tests for the diagnosis of CNS TB.

FIG. 1.

Schematic flowchart of the relationship of the ELISPOT assay results to empirical anti-TB therapy and the final classification of CNS TB. Of the total of 37 patients with suspected CNS TB, 2 patients gave indeterminate results by the PBMC ELISPOT assay. Data for the remaining 35 patients (11 with CNS TB plus 24 with not-active TB) were included in the final analysis of the PBMC ELISPOT assay. Of the 21 patients who agreed to additional CSF sampling, the CSF MCs from 5 patients gave indeterminate results by the ELISPOT assay. Thus, the CSF MC/PBMC ratio was assessed for the remaining 16 patients (4 with CNS TB plus 12 with not active TB) with suspected TB meningitis. ^a, data for 35 patients were included in the final analysis of the PBMC ELISPOT assay; ^b, data for 16 patients were included in the final analysis of the CSF MC ELISPOT assay. MRI, magnetic resonance imaging.

FIG. 2.

Responses to ESAT-6 and CFP-10 according to PBMC ELISPOT assay (A) and CSF MC ELISPOT assay (B) results in patients with suspected CNS TB. Bars, medians; dotted line in panel B, cutoff value; IFN, interferon.

FIG. 3.

Typical results of ELISPOT assay with PBMCs and CSF MCs from patients with tuberculous meningitis (A and B) and aseptic meningitis (C and D). A response was classified as indeterminate if the number of spots for the positive control well was less than 20 or the number of spots for the negative control well was more than 10. A response was classified as positive if the number of spots for ESAT-6 or CFP-10 was six or more after subtraction of the background spots in the negative control well.

FIG. 3.

Typical results of ELISPOT assay with PBMCs and CSF MCs from patients with tuberculous meningitis (A and B) and aseptic meningitis (C and D). A response was classified as indeterminate if the number of spots for the positive control well was less than 20 or the number of spots for the negative control well was more than 10. A response was classified as positive if the number of spots for ESAT-6 or CFP-10 was six or more after subtraction of the background spots in the negative control well.