Human Defenses A gainst Infection. Fighting off the “Bad Guys”. The body possesses many mechanisms that impart nonspecific defense. The objectives of these mechanisms are to prevent microorganisms from gaining a foothold in the body and to destroy them if they penetrate to the deeper tissues.
whitish mass of cells, bacteria,
and debris called pus.
There are two major branches of the immune system: antibody-mediated immunity (also known as humoral immunity) and cell-mediated immunity.
Five classes of antibodies (immunoglobulins)
3.IgAis found in external secretions such as those at the mucosal surfaces of the respiratory, gastrointestinal, and urogenital tracts. It is also present in the tears, saliva, bile, urine, and colostrum, and it is transferred in the breast milk
4. IgD is found in extremely small quantities in the serum. IgD is found at the surface of B-lymphocytes and is believed to be an antigen receptor at this location.
5. IgE, occurs in minute concentrations in the serum and is important in hypersensitivity reactions, especially the anaphylactic reaction. A localized reaction is called allergy.