Selectins are responsible for the initial stickiness of leukocytes to vascular endothelial cells. Bind through sialylated carbohydrate to selectins. ICAM1-3, VCAM on vascular endothelial cells. 104 lymphocytes extravasate every sec through HEV into a single lymph node. Effector and memory lymphocytes have increased levels of adhesion molecules.
Infection leads to increased E and P selectins on endothelial cells.
Respiratory bursts produce oxygen and nitrogen intermediates which kill pathogens and cause tissue damage. Pus - accumulation of dead cells, microorganisms, proteins, fluid. Tissue nacrophages produce TNF a and IL-1 which increase adhesion molecules on vascular endothelial cells. Due to persistence of Ag. IFN g produced by activated T cells and TNF a produced by activated macrophages maintain the activation cycle.