L7 - immune response to ecxtracellular pathogens Flashcards
structure of lymph node and role in inefction
small bean shaped structures
infected tissues drain fluid to lymh node - APCs proscess and present
in paracrotex APCs activate T-cells
in cortex B cells are activated and migrate to secondary folicles with germinal centres (areas of rapid proliferation)
name one of the chmeokines produced by lymph nodes to attract T and B cells
CCL21
binds to CCR7 receptor on Naive T-cells
how do lymphocytes enter lymph node - 4 steps- simple
- Rolling
- activation
- adhesion
- diapedesis
how do lymphocytes enter lymph nodes - detailed
- T-cell enters high-endothelial venule of lymph node
- weak bidning between L-selectins and
addressins of epithelial cells
= rolling movement
- T-cell binds to chemokines changing comformation of integrins increasing affinity
= strong binding
- T-cell enters lymph node through epithelial cells via diapedesis
name the different molecules and receptors involved in the 4 key steps of lymph node entry - rolling,activation , adhesion , diapedises
rolling:
L-selectins
Activation:
chemokines
adhesion:
integrins
diapedesis:
chemokines
what happenes to T-cells that are activated by APCs in lymph node and what happenes if there not (where do they return to blood)
activated T-cells stay in nodes and proliferate
rejoin blood at thoraic duct due to S1P gradient
what is S1P and how does it affect movemt out of lymph nodes for T-cells
Shingosine 1-phosphate
lipid higher conc outisde than insde lymph nodes
on activation T-cells downregulate receptors for S1P
= no longer sensitive to conc gradient
describe how b-cells enter lymph nodes and what happenes
- Circulating B-cells enter via high endothelial venules
- travel towards primary follicle BUT are activated by T-cells on border
- form a primary focus (proliferating B-cells/somatic hypermutation) = light zone
- B-cells can migrate to nearby follicle to form germinal centre (affinity maturation) = dark zone
= undergoes somatic hypermutation and affinity maturation with help of Tfh cells
what organ deals with blood-borne infections
spleen
due to no contact with lymphatic system
3 main functions of antibodies
neutralisation
opsonisation
complement activation - classical pathway
what is Gut-ascociated lymphoid tissue (GALT)
found in instestines
scattered cells and organised peyers patch stuctures
both drained by lymph system
structure of peyers patch
Microfold (M) cells sit over the peyers patch
inbetween epithelial cells
allow movement of antigens into underlyming lymph tissue
antigesn proscessed by APCs
how are Immune cells sent to the lymh node folliwng activation and how do the ‘home’ back
On activation in peyers patch dendritc cells upregulate the ‘lymph node chemokine receptor’
= CCR7
binds to CCL21 - moves to lymph
on activation CCR7 is downregulated and tissue specifc chemokine receptors are upregulated
- same theory works for all immune cells getting to lymph node and back into circulation
why is class switching of B-cells T-cell depndant
binding of CD40 to CD40L by T-cells activates class switching
additionally cytokines produced affect what antibody
= No T-cell = IgM produced
name the cytokine produced by T-cells to cause class switching to IgA B-cells for mucosal sites
TGF-b
