It occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause. Chemicals including histamine, bradykinin, serotonin , and others are released by damaged tissue. These chemicals cause blood vessels to leak fluid into the tissues, resulting in localized swelling . This helps isolate the foreign substance from contact with body tissues. The process where these white blood cells surround, engulf, and destroy foreign substances is called phagocytosis, and the cells are collectively referred to as phagocytes.
Phagocytes eventually die.
Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes. It involves a specific type of white blood cell called a lymphocyte. Actually, there are 2 groups of lymphocytes. Antibodies attach to a specific antigen and make it easier for the phagocytes to destroy the antigen. B cells and T cells develop that are specific for ONE antigen type.