Immune, metabolic, anatomical, and functional features of people after successful tuberculosis treatment: an exploratory analysis

Abstract

We explored the underlying mechanisms that may drive post-tuberculosis (TB) lung disease, a multifactorial, heterogenous, and prevalent disease. Extensive clinical phenotyping through fluorine-18 Fluorodeoxyglucose (FDG) positron emission tomography (PET)-computed tomography (CT) scans, pulmonary function testing, and symptom and quality of life questionnaires, was performed on a cohort of 48 adults who completed TB treatment within 6 months prior. Immunological characteristics of paired blood- and bronchoalveolar lavage fluid (BALF)-derived immune cells were assessed by multiplex bead-based immunoassay, ELISA and flow cytometry. There was agreement between measures of inflammation on PET, the severity of anatomical abnormalities on CT, and pulmonary function testing. However, of these, only PET was associated with exercise tolerance and symptom scores. Measures of radiologic extent (total glycolytic activity and SUVmax on PET, and segments involved on CT) also correlated with proteins detected in blood that implicate type 1 (IFN-γ, TNFα, IL-12) and type 2 (IL-4, IL-33) responses, ongoing remodelling of lung tissue (MMPs), airways and vasculature (VEGF), as well as subsets of activated CD8⁺ and CD4⁺ T-cells. The radiologic extent of structural post-TB lung involvement is associated with a range of impaired lung function measures and immunological dysregulation. Our findings suggest that obstructive and restrictive lung pathology due to pulmonary TB do not occur in opposition but rather point towards a mixed pathology in most TB survivors.

Keywords: FDG PET-CT; Flow cytometry; Luminex; PTLD; Post-Tuberculosis lung disease; Post-tuberculosis sequelae; Pulmonary tuberculosis; Spirometry.

Fig. 1

Transverse and sagittal views of CT images with PET overlay.

Fig. 2

(a) Correlation of quantified imaging variables to pulmonary function. Cross marks indicate non-significance (p ≥.05). Note that increasing lung function values indicate improving function (except for residual volume/total lung capacity ratio) while high imaging values indicate more pathology, hence the inverse correlations. (b): Correlation plot of quantified imaging variables and lung function to effort tolerance tests, symptom scores and clinical variables showing the lack of correlation between these tests.

Fig. 3

(a) Correlation matrix of quantified imaging variables, pulmonary function tests and participant characteristics to protein factors in serum. Cross marks indicate non-significance (p ≥.05). Note that increasing lung function values indicate improving function (except for residual volume/total lung capacity ratio), while high imaging values indicate more pathology, hence the inverse correlations. (b): Correlation matrix of quantified imaging variables, pulmonary function tests and participant characteristics to protein factors in bronchoalveolar lavage fluid.

Fig. 4

Heatmaps displaying correlations of cell phenotypes with clinical features of lung disease. Cells were clustered according to their expression of the markers shown in each expression heatmap. Metaclusters were annotated according to expected phenotypes for memory and functional subsets. Frequencies of each subset were correlated to clinical features of pulmonary function and disease using Kendall’s rank correlation test. The frequency of each subset among the total cell population across all participants is shown as a boxplot. The median expression of markers used in clustering was scaled and is shown for each metacluster, defining cell function and phenotype; the range and median of expression was used to denote expression intensity in each expression heatmap. Figure 4a: CD4 + T cells. Treg were defined as CD25 + CD127 lo/- among total CD4 + cells. Memory phenotypes were inferred by the expression of CD45RA and CD197 among non-Treg CD4 + T cells. Subpopulations of effector T cells were identified by the expression of CD194, CD183, or CD196 among CD4 + CD197- non-Treg cells. Figure 4b: CD8 + T cell subsets were inferred similar to the CD4 + T cell criteria, using the CD8 + CD4- population of T cells. Figure 4c: B cells were clustered according to their expression of CD45RA, CD27, CD25, CD197, CD196, and CD183 among CD19 + CD3- lymphocytes. Activation and memory phenotype was defined by the expression of CD25 for activation and CD27 for memory. Homing was inferred by the expression of CD197 for movement to lymph nodes and CD183 for homing to sites of inflammation.