Fig 1.
eIFNγ amounts released after stimulation of elephant PBMCs by mitogens and antigens.
(A) Schematic representation of PBMC stimulation for IGRA. (B) The eIFN© levels in culture supernatants of PBMCs stimulated by MTBC antigens as indicated in (A). The eIFN© levels were measured by sandwich ELISA. Different color-coded dots represent individual elephants with MTBC infection statuses determined by using the criteria described in previous reports [12].
Fig 2.
Summary of MTBC infection status determined by PBMC cultures for IGRA.
The responses of PBMCs against M. tb antigens by eIFN© secretion were used to determine MTBC infection status. The results are summarized in a heatmap, where an MTBC positive status is shown by red boxes, MTBC infection negative status is shown by green boxes, and infection indeterminate status is shown by yellow boxes.
Fig 3.
Schematic representation of whole blood cultures for IGRA.
(A) Amounts of eIFNγ produced from cells in whole blood cultures after stimulation with different mitogens for 24 h (n = 10). **** p value ≤ 0.0001, and ns indicates not statistically significant with a p value > 0.05. (B) Schematic workflow for whole blood cultures and IGRA for MTBC detection. The figure is created by the authors with BioRender.com.
Fig 4.
Flowchart detailing the interpretation of results from whole blood culture IGRAs.
Based on the IGRA results, the interpretation of infection status is conducted by following steps 1–6. The interpretations results include uninterpreted, MTBC infection negative, MTBC infection positive and MTBC infection indeterminate.
Fig 5.
Results of eIFNγ concentrations obtained by PBMC cultures IGRA (PC) and whole blood cultures IGRA (WC) and summary of result interpretations.
(A) The results are presented as the eIFN© concentrations with comparisons between PBMC assays or whole blood culture assays at the individual level. The MTBC infection statuses were simplified to infection negative (green) or infection positive (red). (B) Fifteen elephant samples were subjected to PBMC cultures for IGRA in parallel with whole blood cultures for IGRA. The results obtained from each assay were interpreted based on the criteria described by Songthammaniphap et al. and above [12]. The interpretations are presented as a heatmap.
Fig 6.
The eIFNγ concentrations obtained by PBMC cultures IGRA (PC) and whole blood cultures IGRA (WC) and summary of result interpretations in elephant cohort with unknown MTBC infection status.
(A) The results are presented as the eIFN© concentrations with comparisons between PBMC assays or whole blood culture assays at the individual level. The MTBC infection statuses were simplified to infection negative (green) or infection positive (red). (B) Nine elephant samples were subjected to PBMC cultures for IGRA in parallel with whole blood cultures for IGRA. The results obtained from each assay were interpreted based on the criteria described by Songthammaniphap et al. and above [12]. The interpretations are presented as a heatmap.