Airway Gland Growth and Differentiation

Very little investigative effort has been directed at the mechanisms mediating growth of airway submucosal glands. This is surprising in view of substantive evidence linking gland growth with hypersecretion both in chronic bronchitis ( 1 , 2 ) and cystic fibrosis ( 3 ). The existing information on airway gland growth is almost exclusively confined to morphological descriptions. These focus on human ( 4 – 9 ), rat, dog, sheep ( 10 ) opossum ( 11 ), monkey ( 12 ), and ferret ( 13 ). Basic principles of gland growth garnered from the descriptive studies are summarized below. Left unanswered are questions concerning the identity of the gland progenitor cell, the identity of growth factors controlling gland growth, the identity of enzymatic mechanisms permitting gland invasion of connective tissue, and the nature of epithelial-mesenchymal interactions controlling cell differentiation. In this chapter, literature from other fields is brought to bear on these questions and our own recent data are summarized where appropriate.