Inducible Bronchus-Associated Lymphoid Tissue: Taming Inflammation in the Lung

Abstract

Following pulmonary inflammation, leukocytes that infiltrate the lung often assemble into structures known as inducible Bronchus-Associated Lymphoid Tissue (iBALT). Like conventional lymphoid organs, areas of iBALT have segregated B and T cell areas, specialized stromal cells, high endothelial venules, and lymphatic vessels. After inflammation is resolved, iBALT is maintained for months, independently of inflammation. Once iBALT is formed, it participates in immune responses to pulmonary antigens, including those that are unrelated to the iBALT-initiating antigen, and often alters the clinical course of disease. However, the mechanisms that govern immune responses in iBALT and determine how iBALT impacts local and systemic immunity are poorly understood. Here, we review our current understanding of iBALT formation and discuss how iBALT participates in pulmonary immunity.

Interactions between Type 1 Interferons and the Th17 Response in Tuberculosis: Lessons Learned from Autoimmune Diseases

“…This is due to the essential roles of IL-23 and IL-17 in the local formation of tertiary lymphoid structures (TLS) (199, 200). These structures are formed during early infection but can persist for longer periods of time and are associated with protective immunity in Mtb-infected mice (199, 201) (Table 4; Figure 4).…”

Anatomical Uniqueness of the Mucosal Immune System (GALT, NALT, iBALT) for the Induction and Regulation of Mucosal Immunity and Tolerance

“…Nevertheless, humans with chronic lung diseases such as chronic obstructive pulmonary disease [221À223], hypersensitivity pneumonitis [224], and even pulmonary complications of rheumatoid arthritis [225À227] have many well-developed BALT-like areas that seem to react with local antigens. Moreover, mice also develop BALT-like structures in their lungs following pulmonary infection or inflammation [228] (Fig. 2.6).…”

“…2.6). These findings suggest that the BALT-like areas in humans and mice are not true SLOs that develop during embryogenesis but instead are ectopic or tertiary lymphoid tissues that develop in response to local inflammation [228,229]. Interestingly, some mammals, such as pigs and goats, develop BALT during gestation [215,230À233], apparently independent of exposure to antigen or microbes, suggesting that in these species, BALT is a true SLO.…”

“…Numerous inflammatory or infectious stimuli can trigger the formation of iBALT via a variety of pathways [228]. However, many of the core mechanisms involved in SLO development are also involved in the formation of iBALT.…”

“…Importantly, IL-17 is required for iBALT formation only under some conditions, most notably bacterial infections or exposure to bacterial products [228]. However, under other conditions, such as intranasal infection with modified vaccinia virus Ankara (MVA), iBALT forms independently of IL-17 [241].…”