Clinical application of a rapid lung-orientated immunoassay in individuals with possible tuberculosis.
BACKGROUND
Immunological ex vivo assays to diagnose tuberculosis (TB) have great potential but have largely been blood-based and poorly evaluated in active TB. Lung sampling enables combined microbiological and immunological testing and uses higher frequency antigen-specific responses than in blood.


METHODS
A prospective evaluation was undertaken of a flow cytometric assay measuring the percentage of interferon-gamma synthetic CD4+ lymphocytes following stimulation with purified protein derivative of Mycobacterium tuberculosis (PPD) in bronchoalveolar lavage fluid from 250 sputum smear-negative individuals with possible TB. A positive assay was defined as >1.5%.


RESULTS
Of those who underwent lavage and were diagnosed with active TB, 95% (106/111) had a positive immunoassay (95% CI 89% to 98%). In 139 individuals deemed not to have active TB, 105 (76%) were immunoassay negative (95% CI 68% to 82%). Of the remaining 24% (34 cases) with a positive immunoassay, a substantial proportion had evidence of untreated TB; in two of these active TB was subsequently diagnosed. Assay performance was unaffected by HIV status, disease site or BCG vaccination. In culture-positive pulmonary cases, response to PPD was more sensitive than nucleic acid amplification testing (94% vs 73%). The use of early secretory antigen target-6 (ESAT-6) responses in 71 subjects was no better than PPD, and 19% of those with culture-confirmed TB and a positive PPD immunoassay had no detectable response to ESAT-6.


CONCLUSIONS
These findings suggest that lung-orientated immunological investigation is a potentially powerful tool in diagnosing individuals with sputum smear-negative active TB, regardless of HIV serostatus.
Department of Immunology, Royal Free and University College Medical School, London, UK. r.breen@doctors.org.uk
R A M
RA
Breen
S M
SM
Barry
C J
CJ
Smith
R J
RJ
Shorten
J P
JP
Dilworth
I
I
Cropley
T D
TD
McHugh
S H
SH
Gillespie
G
G
Janossy
M C I
MC
Lipman
D000328:Adult; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology*; D016516:CD4-CD8 Ratio; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007202:Indicators and Reagents; D007371:Interferon-gamma / Q000276:immunology; D008214:Lymphocytes / Q000276:immunology; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D011446:Prospective Studies; D012372:ROC Curve; D014373:Tuberculin; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis*
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D007202:Indicators and Reagents; D014373:Tuberculin; D007371:Interferon-gamma