35: Immunology of GI Tract - Steele Flashcards
most abundant Ig isotype in body
IgA
protects the mucosal sites
what are tertiary lymphoid sites?
skin, lungs, and GU tracts
have antibody and cell-mediated cytotoxicity to prevent microbial invasion and infection
GALT =
gut assoc. lymphoid tissue
- these are mucosal inductive sites
- includes peyer’s patches, appendix, lymphoid aggregates in appendix and lg intestine, lymphoid cells in laminal propria
most GALT sites have distinct B cell and T cell areas with antigen presenting cells present
where are peyer’s patches located?
in laminal propria
they are important in promoting IgA production and CTL responses
describe how peyer’s patches work in immune responses
M cells transfer antigens from the gut lumen to the lymphid tissue by endocytosis or phagocytosis
antigens are presented by APCs to T helper cells
T helped cells stimulate antigen specific B cells to form germinal centers
IEL intraepithelial lympthocytes are composed primarily of ..
T lymphocytes
one IEL for every 4-6 epithelial cells in the intestinal lumen
allows cell-mediated immunity against viral and intracellular bacterial infection s
cells in lamina propria composed mainly of…
CD4+ T cells (b lymphocytes, plasma cells, macrophages, dendritic cells, eosinophils and mast cells)
how are plasma cells used in immune response in GI tract?
pre-plasma cells leave the peyer’s patch through lymphatic capillaries and migrate via mesenteric lymph channels to the bloodstream via the thoracic duct
the blood stream takes them “home” to gut
pre-plasma cells become plasma cells and secrete IgA
role of secretory component with IgA dimer
increase the half life of IgA
what is the role of IgA?
major immunoglobulin in secretions (monomeric in serum and dimeric in mucosa) (two subclasses)
IgA1 can fix complement via the alternate cascade; IgA2 can’t
prevents binding of microbes to epithelia and facilitates expulsion
why do you see an increase in plasma IgA with obstructive jaundice?
IgA from the lamina propria is transported via the hepatic portal vein to the liver; in liver sinusoids hepatocytes express the polyIg Receptor and transport IgA
IgA drain froms canaliculi to common bile duct and is deleivered to duodenum in bile
significance of gamma/delta t cells
respond to nonpeptide molecules
may serve as “first responders”
importance of mast cells
- located beneath epithelia exposed to environment (lungs, skin, GI)
- IgE mediated defenese against parasites and allergic reactions
high v. low dose oral tolerance
high: clonal deletion of antigen-specific lymphocytes
low: clonal unresponsiveness and regulatory T cells suppress immune response
most common immunodeficiency in humans
selective IgA deficiency
IgM will usually compensate for absence –> no clinical issues
