In vitro polyfunctional CD4 T cell correlates of diagnostic tests for latent TB in HIV-infected subjects
Methods: HIV+ adults recruited in Kampala, Uganda were differentiated into 2 groups: LTBI (>5mm response to the tuberculin skin test (TST) and negative chest x-ray; n=15), or TST- (TST <5 mm and chest x-ray; n=15). Interferon gamma release assay (IGRA) was also performed for each subject. Multicolor flow analysis was performed on PBMC stimulated with either PPD or mitogen, and frequencies of IL-2, IL-17, IFN-γ and TNF-α secreting cells were determined within the memory subset of CD4 T cells. Polyfunctionality was determined using FlowJo and SPICE software.
Results: PPD-specific CD4+ T cell secretion of TNF-α and IFN-γ was higher in LTBI compared with TST- group (p=0.001 and p=0.002 respectively). In the IGRA+ group there was greater secretion of TNF-α compared with IGRA- though this difference was borderline (p=0.05). IL-2, IFN-γ and TNF-α all correlated with clinical response in terms size of PPD-induced induration or IGRA. Frequency of polyfunctional cells among the TST+ group was greater than and IGRA+ (p=0.04). TNF-α was the dominant cytokine in the TST+ group as 4/5 phenotypes of responding cells all generate either TNF-α alone or in combination with IFN-γ or IL-2. Both TNF-α and IL-2 were dominant among the single cytokine secretors in IGRA+ group. IFN-γ secreting cells are much more frequent in TST+ than IGRA+ subjects.
Conclusion: CD4+ T cell cytokine responses to TB-specific antigens were significantly higher in LTBI compared to TST- HIV+ adults. While IL-2, IFN-γ and TNF-α all appear to be correlates of LTBI, TNF-α is the dominant cytokine in this regard. Perhaps measurement of TNF-α secretors to diagnostic testing for latent TB could add sensitivity but may reduce specificity. Differences exist between polyfunctional cytokine profiles of TST+ and IGRA+ HIV+ individuals which may account for difference in test performance.
P. Van Epps,
H. Aung, None
M. Betts, None
Z. Toosi, None
D. Canaday, None