Reversion and conversion of Mycobacterium tuberculosis IFN-gamma ELISpot results during anti-tuberculous treatment in HIV-infected children.
BACKGROUND
Recent interest has focused on the potential use of serial interferon gamma (IFN-gamma) release assay (IGRA) measurements to assess the response to anti-tuberculous (TB) treatment. The kinetics of IFN-gamma responses to Mycobacterium tuberculosis (MTB) antigens in HIV-infected children during treatment have not however been previously investigated.


METHODS
IFN-gamma responses to the MTB antigens, ESAT-6, CFP-10 and PPD were measured by an enzyme-linked immunospot assay (IFN-gamma ELISpot) at presentation and at one, two and six months after starting anti-tuberculous treatment in HIV-infected children with definite or probable TB. Responses at different time points were compared using a Mann-Whitney U test with paired data analysed using the Wilcoxon signed rank test. A Fisher's exact or Chi-squared test was used to compare proportions when test results were analysed as dichotomous outcomes.


RESULTS
Of 102 children with suspected TB, 22 (21%) had definite TB and 24 (23%) probable TB. At least one follow up IFN-gamma ELISpot assay result was available for 31 (67%) of the 46 children. In children with definite or probable TB in whom the IFN-gamma ELISpot assay result was positive at presentation, anti-tuberculous treatment was accompanied by a significant decrease in both the magnitude of the IFN-gamma response to individual or combined MTB-specific antigens (ESAT-6 median 110 SFCs/106 PBMC (IQR 65-305) at presentation vs. 15 (10-115) at six months, p = 0.04; CFP-10 177 (48-508) vs. 20 (5-165), p = 0.004, ESAT-6 or CFP-10 median 250 SFCs/106 PBMC (IQR 94-508) vs. 25 (10-165), p = 0.004) and in the proportion of children with a positive IFN-gamma ELISpot assay (Fisher's exact test: ESAT-6 15/0 vs 5/11, p = 0.0002, CFP-10 22/0 vs 8/17, p = 0.0001, ESAT-6 or CFP-10 22/0 vs. 9/17, p= 0.002). However almost half of the children had a positive IFN-gamma ELISpot assay after six months of anti-tuberculous treatment. In addition, there was conversion of the IFN-gamma ELISpot assay result during anti-tuberculous therapy in six of 12 children in whom the initial IFN-gamma ELISpot assay was negative.


CONCLUSIONS
In HIV-infected children with definite or probable TB, anti-tuberculosis treatment is accompanied by a reduction in the magnitude of the IFN-gamma ELISpot response to MTB-antigens. However, serial IFN-gamma ELISpot measurements appear to have limited clinical utility in assessing a successful response to anti-tuberculous treatment in HIV infected children.
Connell
Tom G
TG
Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa. tom.connell@rch.org.au
Davies
Mary-Ann
MA
Johannisen
Christine
C
Wood
Kathryn
K
Pienaar
Sandy
S
Wilkinson
Katalin A
KA
Wilkinson
Robert J
RJ
Zar
Heather J
HJ
Beatty
David
D
Nicol
Mark P
MP
Curtis
Nigel
N
Eley
Brian
B
D000818:Animals; D000942:Antigens, Bacterial; D002675:Child, Preschool; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D015658:HIV Infections / Q000150:complications*; D006801:Humans; D007223:Infant; D007371:Interferon-gamma / Q000378:metabolism*; D008297:Male; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D014376:Tuberculosis / Q000188:drug therapy* / Q000276:immunology*
D000942:Antigens, Bacterial; D007371:Interferon-gamma