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Bronchus-associated lymphoid tissue (BALT) comprises submucosal lymphoid cells analogous to Peyer’s patches but located in association with large airways. It is generally not found in normal mouse or human lung tissue. Pulmonary infection or inflammation in mice leads to the development of lymphoid follicles that are not restricted to the upper airways, termed inducible BALT (iBALT). In this study the authors examined lung biopsies from patients with a variety of interstitial diseases including idiopathic pulmonary fibrosis, hypersensitivity pneumonitis and lung disease in association with rheumatoid arthritis (RA) and Sjogren’s syndrome (SS). Although small amounts of lymphoid aggregates were found in the non-autoimmune conditions, samples from the patients with RA and SS had more and larger lymphoid areas.
The authors then proceeded to investigate the potential roles and causes of this well-organised iBALT. First, venules and lymphatic vessels were consistently found within the follicles and it was felt they were likely to facilitate entry and exit of immune cells. Second, levels of certain cytokines involved in lymphoid organogenesis and TH2-driven pathology, as well as levels of the autoantibody anti-cyclic citrullinated peptide (anti-CCP) in BAL fluid, correlated well with the amount of iBALT. Third, dense areas of collagen deposition and myofibroblast activity around the follicles were seen in the patients with highly organised iBALT.
These findings suggest that iBALT may have a significant role in the pathogenesis of interstitial lung disease seen in association with connective tissue disorders. Further understanding of the mechanisms involved could be used to develop novel treatments.
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