is further maintained by bronchial smooth muscle; the larger bronchi and the trachea are supported as well by cartilaginous rings. All of the cells that make up the tissues of the upper and lower airway—epithelial cells, fibroblasts, cartilage cells, smooth muscle cells, blood vessels comprising endothelial and vascular smooth muscle cells, nervous tissue, and resident nonactivated inflammatory cells, such as mast cells—can and do respond to inhaled materials with nonspecific host defense (Hunninghake et al., 1979). Moreover, once such a response has been evoked, there may be a further influx of immune and inflammatory cells to the airway.

A wide variety of immune and inflammatory cells are involved in airway responses to inhaled proteins in the bronchi as well as in the upper and lower airways. Specific responses are initiated by interacting sets of cells composed of macrophages and other significant antigen-presenting cells, as well as lymphocytes—in particular, T helper lymphocytes (although other forms of T lymphocytes and B cells are also involved in this response). Figure 4-1 shows the interaction of allergen with relevant immune and inflammatory

FIGURE 4-1 Immune cells and their interactions with allergens.