Regulation of antigen-presenting cell function(s) in lung and airway tissues.

A variety of cell populations present in respiratory tract tissues can express the function-associated molecules on their surface which are required for presentation of antigen to T-lymphocyte receptors. However, the potential role of individual cell populations in regulation of local T-lymphocyte-dependent immune reactions in the lung and airways depends on a variety of additional factors, including their precise localisation, migration characteristics, expression of T-cell "co-stimulatory" signals, responsiveness to inflammatory (in particular cytokine) stimuli, host immune status, and the nature of the antigen challenge. Recent evidence (reviewed below) suggests that the induction of primary immunity (viz. "sensitisation") to inhaled antigens is normally controlled by specialised populations of Dendritic Cells, which perform a surveillance role within the epithelia of the upper and lower respiratory tract; in the pre-sensitised host, a variety of other cell populations (both bone-marrow derived and mesenchymal) may participate in re-stimulation of "memory" T-lymphocytes.