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A4319 - Bronchoscopic PPD Challenge in the Assessment of Parenchymal Lung CD4+ T Cells in Humans with Latent Tuberculosis Infection
Author Block: R. F. Silver1, S. Weigel1, M. Moyer1, J. R. Jarvela2; 1Pulmonary, Critical Care, and Sleep Medicine, Case Western Reserve University School of Medicine and the Louis Stokes Cleveland VA Medical Center, Cleveland, OH, United States, 2Pulmonary, Critical Care and Sleep Medicine, Case Western Reserve University School of Medicine and the Louis Stokes Cleveland VA Medical Center, Cleveland, OH, United States.
INTRODUCTION: Recent murine studies have utilized intravenous (IV) antibody injection to distinguish vascular-associated (IV+) and parenchymal (IV-) lung CD4+ T-cell populations during M. tuberculosis (Mtb) infection. These populations differ in their levels of differentiation, their surface markers, and their abilities to contain aerosol Mtb challenge. Human studies of pulmonary immunity can only routinely sample airway T cells using bronchoalveolar lavage (BAL). We therefore we sought to investigate the relationship between these cells and those of other lung compartments by assessing markers associated with IV+ and IV- populations in Mtb-repsonsive CD4+ T cells of individuals with latent tuberculosis infection (LTBI). We compared phenotypes of CD4+ T cells from peripheral blood with those obtained by BAL at baseline and following bronchoscope challenge with purified protein derivative of Mtb (PPD).
METHODS: Otherwise healthy non-smokers with LTBI were recruited to undergo research bronchoscopy procedures. After obtaining a baseline BAL sample, saline alone was instilled into one lung subsegment and challenge instillation of PPD (0.5 tuberculin units) was placed into a comparable subsegment of the contralateral lung. After 48 hours, BAL of both control and PPD-challenged segments was obtained. Expression of markers characteristic of vascular-associated and parenchymal lung CD4+ T cells (CX3CR1, CXCR3, KLRG1, PD1, and CD69) was evaluated on Mtb-responsive CD4+ T cells (identified by intracellular staining for Mtb-induced IFNγ production) in peripheral blood and in BAL obtained both at baseline and 48 hours after PPD challenge.
RESULTS: As we have reported previously, compared to peripheral blood, BAL of LTBI subjects both at baseline and following PPD challenge is greatly enriched for Mtb-responsive CD4+ T cells. IFNγ+ CD4+ T cells of baseline BAL display much greater expression of CXCR3 than do those of peripheral blood; these cells are also overwhelmingly KLRG1- and CD69+. Following PPD challenge, the phenotype of Mtb-responsive CD4+ T cells is largely similar to those of baseline BAL, with the exception that CXCR3 expression is lower. Given that CX3CR1 expression is not increased in a reciprocal manner, it may be that this change reflects transient downregulation of CXCR3 following its activation by specific chemokine ligands.
CONCLUSIONS: Our findings suggest that airway Mtb-responsive CD4+ T cells obtainable by BAL are not representative of circulating Mtb-responsive cells. Instead, these cells may both migrate from and be reflective of lung parenchymal CD4+ T cells, which may be of particular relevance to assessment and quantification of protective immunity to Mtb within the human lung.