In the bronchi, there is extensive associated lymphoid tissue (BALT),
which is analogous to the mucosa-associated lymphoid tissue (MALT) of the
gut and the skin-associated lymphoid tissue (SALT). There are B and T cell
areas throughout the BALT. The B cells are precursors of plasma cells and
synthesize immunoglobulins such as IgA associated with the bronchial secre-
tion. Helper T cells recognize foreign antigen in association with class II
major histocompatibility complex (MHC) molecules. Cytotoxic T cells rec-
ognize fragments of antigen (specifically viral fragments) on the surface of
viral-infected cells in association with class I MHC. Antigen-presenting
cells (i.e., alveolar macrophages) also function in a similar fashion to those
found elsewhere in the body; they present antigen to helper T cells in con-
junction with class II MHC.
192.The answer is d.(Kumar, p 109. Lobov, pp 11205-11210).Angiostatin
and endostatin are cleavage products of plasminogen and type XVIII collagen
respectively and function as anti-angiogenic peptides. Vascular endothelial
growth factor (VEGF, answer a) stimulates the recruitment and growth of
endothelial cells through the VEGF-R located on endothelial cell precur-
sors as well as endothelial cells. Platelet-derived growth factor (PDGF)
recruits smooth muscle cells (answer b)and transforming growth factor-
beta (TGF-β) stimulates and stabilizes extracellular matrix production.
Recruitment and proliferation of periendothelial cells (answer e),smooth
muscle cells, pericytes, and fibroblasts are required for development and
maturation of new blood vessels. The angiopoietins (Ang) 1 and 2 bind
their receptor, Tie2, a receptor tyrosine kinase which regulates endothelial
cell proliterative status. Ang 1 binds Tie2 leading to periendothelial cell
recruitment and therefore vascular maturation.
Ang 2 is found in organs of the female reproductive tract and blocks
Ang 1 effects when VEGF is absent. The result is regression of the blood
vessel. Ang 2 in the presence of VEGF leads to loosening of the surrounding
cells permitting multiplication of endothelialcells and angiogenesis.
300 Anatomy, Histology, and Cell Biology