Bronchus-associated lymphoid tissue and the source of immunoglobulin-containing cells in the mucosa.

Bronchus-associated lymphoid tissue has major morphologic and functional similarities to Peyer's patches found in the gut. Both possess a lymphoepithelium with selective antigen sampling properties, both appear in the apparent absence of direct antigen stimulation, both contain a high percentage of cells bearing IgA sdurface immunoglobulin and both can repopulate the bronchial and gut lamina propria with IgA containing cells. Good evidence now exists (and will be reviewed) in support of the concept of a common mucosal immunologic system. Cells potentially sensitized at or in a mucosal tissue such as the gut or lung would then migrate to the draining lymph node, thence into the circulation and localize in a variety of mucosal tissues. Factors involved but not essential for such localization include antigen. Lymphoblasts derived from the lung tend to go back to the lung. Similarly, gut derived lymphoblasts have a predilection for the gut. However, available evidence supports the concept of integrated systemic and mucosal immune systems. Several factors must be taken into account in analysis of the products of local mucosal immune reactions and in developing approaches to achieve optimal humoral immunity at any mucosal surface.