Study Set Content:
The weak rolling interactions slow down the leukocytes and give them the opportunity to bind more firmly to the endothelium.
Integrins
Firm adhesion is mediated by a family of heterodimeric leukocyte surface proteins called
Integrins
TNF and IL-1 induce endothelial expression of ligands for integrins, mainly:
- VCAM-1
- Ligand for the B1 integrin VLA-4
- ICAM-1
- Ligand for B2 integrins LFA-1 and MAC-1
migration of the leukocytes through intact endothelium, called
transmigration or diapedesis
Transmigration of leukocytes occurs mainly in
Postcapillary venules
These molecules are present in the intercellular junctions between endothelial cells which are involved in the migration of leukocytes.
CD31 or PECAM-1
After exiting the circulation, leukocytes move in the tissues toward the site of injury by a process called
Chemotaxis
defined as locomotion along a chemical gradient
Chemotaxis
The most common exogenous factor
bacterial products, including peptides with N-formylmethionine terminal amino acids
Endogenous chemoattractants include several chemical mediators which are:
- Cytokines - IL-8
- Components of Complement System - C5a
- Arachidonic acid metabolites - leukotriene B (LTB4)
The nature of the leukocyte infiltrate varies with the
Age of inflammatory response & type of stimulus
Neutrophils predominate during,
6 to 24 hours
neutrophils predominate in the inflammatory infiltrate during the first 6 to 24 hours and are replaced by monocytes in
24 to 48 hours
The two major vasoactive amines, so named because they have important actions on blood vessels
Histamine and Serotonin
The richest source of histamine
Mast Cells
Histamine triggers:
- Physical Injury
- Binding of antigen to IgE antibodies
- Anaphylatoxins (C3a and C5a)
- Neuropeptides (substance P)
- Cytokines (IL-1, IL-8)
dilation of arterioles and increases the permeability of venules.
Histamine
the principal mediator of the immediate transient phase of increased vascular permeability, producing interendothelial gaps in venules
Histamine
preformed vasoactive mediator present in platelets and certain neuroendocrine cells, such as in the gastrointestinal tract
Serotonin (5-hydroxytryptamine)
neurotransmitter in the gastrointestinal tract and the central nervous system;It is also a vasoconstrictor,
Serotonin
