Increased vascular permeability is the first mechanism. It allows the escape of plasma proteins and white cells. This is known as exudation. The most important chemotactic factors for both neutrophils and macrophages include C5a, a compnent of the complement system, leukotriene B4, a product of arachidonic acid metabolism, and bacterial products. Macrophages are also attracted by the basic peptides in the lysosomal granules of neutrophils and this explains whythey appear as the second line of defense.
Repair is the process by which lost or destroyed cells are replaced by new, living cells.
The tissue defect is initially filled up with highly vascularized connective tissue called granulation tissue. It consists of newly formed small blood cells embedded in loose ground substance containing fibroblasts and inflammatory cells. As granulation tissue matures, inflammatory cells decrease in number, fibroblasts lay down collagen, and the capillaries become less prominent. An avascular, relatively acellular tissue with inactive spindle-shaped fbroblasts tucked in between collagen fibers emerges. The collagen fibers then aggregate into mature fibrils.