3) MadCAM1 - endothel of GALT - binds L-selectin of lymphos
4) PECAM1 (CD31) - plts, leuk and endoth (?not clear) - NB for transmigration?
Name the integrins, where they are expressed and what they bind.
Made of up a and b chains, expressed on many cell types - bind to endoth, leuk, ECM
1) B2 integrins (CD11/CD18) - all leukocytes - bind ICAM1 on endoth cells - adhesion, arrest, transmig
CD11a-c/CD18, so CD11a is LFA1, a1; CD11b is Mac1, a2; CD11c is CR4 or p150,9; CD18 is b2 int
LFA1: lymphs and other leuk with other cells, endoth
Mac1 or CR4 - attachment of leuk to endoth and extravasation
Mac1 also fib receptor and C receptor on phag cells allowing binding of optimized particles
2) B1 integrins (VLA4) - eos, monos,lymphs - bind VCAM1 - adhesion (not on neuts) to endothelium
Some integrins bind RGD sequences of fibronectin, vitronectin, laminin and other ECM components
Name the mucin-like glycoproteins, where they are expressed and what they bind to.
1) Heparan sulfate - on cell surfaces and ECM - binds CD44 (leuk adhesion molecule)
2) GlyCAM1 - HEVs of LNs - binds L-selectin
3) CD34 - on endoth and BM cells - binds L-selectin
4) ESL1 and PSGL1 - on leukocytes?
What are the three steps to leukocyte recruitment to sites of injury/infection?
1) Induction of adhesion molecules
PAF, hist, thrombin ---- release of P-selectin from WP and a granules
IL1, TNF ---- expression of various adhesion molecules on leuk and endoth and ligands for integrins on endoth (VCAM, ICAM)
2) Activation of leukocytes: chemokines bind to endothelial cell hep sulfate - activate rolling leukocytes AND get conversion of VLA4 and LFA1 from low affinity to high affinity - SO ROLLING STOPS/FIRM ADHESION
3) Migration through endothelium: chemokines produce chemical concentration gradient, PECAM1 expressed on endoth cells near jxns binding to other PECAM1, leuk secrete collegenases to get through BM, once through they bind to ECM with B1 integrins and CD44
Name chemotactic factors:
1) Endogenous: C5a, LTB4, IL8 (others of these types also involved but these are most NB)
2) Exogenous: bacterial products - N-formyl-meth aa
How do chemotactic factors exert their effects?
1) Bind GProt coupled receptors on WBC
2) Recruit G protein
3) Activate effector molecules: PLC, PI3K, protein tyrosine kinases --- increase cytosolic Ca
4) This activates GTPases and kinases ---- polymerizes actin ---- WBC movement
5) Actin regulating proteins - filamin, gelsolin, profilin, calmodulin - interact with a and m to contract
What is the end result of signalling pathways triggered in leukocytes during activation?
1) Increase cytosolic Ca
2) Activation of protein kinase C and phospolipase A2
What are the functional responses of leukocyte activiation?
1) Prod of AA metabolites from PLs - d/t activation of PL A2 by incr. Ca
2) Degran and secretion of lysosomal enz and activation of oxidative burst
3) Secretion of cytokines
4) Modulation of adhesion mol, increased avidity of intergrins allowing for firm adhesion
Name the receptors involved in leukocyte activation.
1) TLRs - activate leukocytes in response to infectious agents
2) GPCRs - on most leukocytes, have diverse ligands ex. C5a, chemokines, NFM residues,
When ligand binds receptor - GTP replaces GDP (in resting recetor) - activates enzymes - incl PLC which degrades inositol PLs -- incr Ca --- activates protein kinase C
GPCR - also stim cytoskel changes (see prev Q) and increase motility
3) Cytokine receptors: ex. IFNg - secreted by NK cells and Tcells --- macrophage activation
4) Opsonin receptors: best opsonins - IgG, C3, but also: MBL, fibronectin, fib, CRP
What are the three steps of phagocytosis?
Mannose receptor: binds sugars (mannose and fructose) of microbial cell walls (not found at terminals of mammalian cells)
Scavenger receptors: bind variety of microbes and LDL
Integrins ex. CD11b/CD18 (MAC1) binds microbes
2) Engulfment: pseudopods (polymerizing actin filaments) form around particle, engulf, then fuse with lysosome (phagolys), note that pinocytosis not dependent on actin (instead via clathrin coated pits - Tf)
3) Killing: O2 dep mech, phag stim bust in O2 consumption, glycogenolysis, glucose oxidation --- ROS
Explain how bacterial killing occurs after phagocytosis (O2 dep).
1) Activation of NADPH oxidase - pulls e off NADPH ---- NADP and gives to O2 leaving O2-
2) O2- dismutates to H2O2 which then reacts with Fe2+ and results in OH- or with MPO and Cl (halide) it is converted to hypoclorite and destroys organisms by halogenation or lipid peroxidation
Resting neuts have NADPH oxidase in plasma mem and cyto but when activated they go to membrane and phagosome membrane
ROS and NO produced in the phagolysosome protecting the cell