Analysis of cellular and soluble profiles in QuantiFERON nonconverters, converters, and reverters in the Gambia

Abstract

Background Tuberculosis (TB) is the leading cause of death from a single infectious agent worldwide. The immune system is capable of clearing the pathogen before establishment of latent infection but the mechanisms for this are not yet understood. Methods This study analysed highly exposed household contacts (HHC) of TB index cases who were categorised according to QuantiFERON (QFT) results at recruitment and 6 months. Seventeen (17) QFT nonconverters, 14 QFT converters, 18 QFT reverters and 18 latent TB infection (LTBI) were analysed. Supernatants generated following QFT stimulation at both time‐points were analysed using a 64‐plex cytokine array. Flow cytometry was performed on QFT converters and nonconverters at baseline only. Results Interleukin‐2 (IL‐2), IL‐5, IL‐13, APRIL, IL‐17A, IP‐10, MIP‐1ß, sIL‐6rb, OPN, and sTNFR2 were all significantly higher in the QFT converters compared with nonconverters at baseline. Levels of interferon‐α2 (IFN‐α2) and IL‐2 were significantly lower in QFT reverters compared with nonconverters at baseline. Analysis of Ag‐specific IL‐2 levels resulted in an area under the curve (AUC) of 0.93 (95% confidence interval [CI], 0.84‐1.00) for QFT converters compared to nonconverters and an AUC of 0.80 (0.65‐0.95) for QFT reverters compared with LTBI. Purified protein derivative (PPD)‐specific CD4 + CD26 + IFN‐γ + cells were significantly increased (P = .0007) in QFT nonconverters compared with QFT converters at baseline. Conclusions Our results provide insight into the underlying mechanisms of resistance to sustained Mycobacterium tuberculosis infection.

Phenotype Definition for “Resisters” to Mycobacterium tuberculosis Infection in the Literature—A Review and Recommendations

“…Medawar et al. included HHC who were highly exposed based on sleeping in the same bedroom as the TB index case only ( 20 ). In another study, Vorkas et al.…”

“…This could also be indicative of participants who were recently infected and then possibly cleared infection. More reliable cut-offs for IGRA negativity set as values less than 0.2 IU/ml and > 0.7 IU/ml for a positive IGRA have been suggested ( 20 , 31 ). Using these stricter definitions, they show that stringent nonconverters are less likely to develop TB over 2 years compared to recently converted or persistently QFT positive persons ( 31 , 56 ).…”

“…Studies investigating adaptive response using additional immunological assays show IFN-γ independent T-cell responses, differences in T-cell receptors, as well as the presence of antibodies in many of the studies ( 4 , 20 , 21 , 25 , 29 , 34 ). This highlights the significance of avoiding terms such as innate or adaptive resistance until both mechanisms have been further illustrated.…”

“…Exposure was measured by the smear grade of the index patient as well as sleeping proximity to the index patient ( 19 ). In a second study the group selected HHC from another longitudinal HHC cohort study ( 20 ). High exposure was defined by sleeping proximity and only persons sleeping in the same room as the index case was included.…”

“…Seventeen (25%) were defined as “QFT nonconverters” based on 2 negative readings, 14 (21%) as “QFT converter” based on a negative at baseline and positive after 6 months, 18 (27%) as “QFT reverter” based on positive at baseline and negative after 6 months and lastly 18 (27%) as “LTBI” based on 2 positive readings. A QFT was considered negative if IFN-γ (TB Ag – Nil) < 0.2 IU/ml and positive if IFN-γ (TB Ag – Nil) > 0.7 IU/ml, which avoided what they referred to as the “grey zone” ( 20 ). It is not clear whether the participants represented in these two studies originated from the same cohort.…”