Bronchus-associated lymphoid tissue (BALT) structure and function

Abstract

Bronchus-associated lymphoid tissue (BALT) is a constitutive mucosal lymphoid tissue adjacent to major airways in some mammalian species, including rats and rabbits, but not humans or mice. A related tissue, inducible BALT (iBALT), is an ectopic lymphoid tissue that is formed upon inflammation or infection in both mice and humans and can be found throughout the lung. Both BALT and iBALT acquire antigens from the airways and initiate local immune responses and maintain memory cells in the lungs. Here, we discuss the development and function of BALT and iBALT in the context of pulmonary immunity to infectious agents, tumors, and allergens as well as autoimmunity and inflammatory diseases of the lung.

Figure 7.1

Organization of murine BALT. Lungs from mice infected with influenza 12 days previously were frozen in OCT medium and sectioned on a cryostat. Sections were probed with antibodies to B220 (blue), CD3 (red), and CD11c (green). Note the presence of three B220+ B cell follicles, two of which are underneath a major airway. CD3+ T cell zones are between the follicles and some T cells are scattered in the follicles. CD11c+ DCs are located primarily in the T cell zones.

Figure 7.2

IgG-secreting cells in murine BALT. Lungs from mice infected with influenza 10 days previously were frozen in OCT medium and sectioned on a cryostat. Sections were probed with antibodies to B220 (white), IgG (green), and CD3 (red) and were counterstained with DAPI (blue). Note that the architecture is not well developed and the B220+ B cells, CD3+ T cells, and IgG+ plasma cells are intermixed.

Figure 7.3

FDCs in human BALT. A formalin-fixed, paraffin-embedded lung biopsy from a patient with hypersensitivity pneumonitis was sectioned on a microtome and probed with an antibody to CD21 (red) and counterstained with DAPI (blue). Note the robust FDC network and the way the follicular areas are partially separated from the rest of the tissue.