Immunoglobulin A (IgA) is an antiboy playing a critical role in mucosal immunity. More IgA is produced in mucosal linings than all other types of antibody combined. However, sources are correct when they indicate immunoglobulin G as the most common form of immunoglobulin in the human body. In its secretory form, is the main immunoglobulin found in mucous secretions, including tears, saliva, colostrum, intestinal juice, vaginal fluid and secretions from the prostate and respiratory epithelium. It is also found in small amounts in blood. Because it is resistant to degradation by enzymes, secretory IgA can survive in harsh environments such as the digestive and respiratory tracts, to provide protection against microbes that multiply in body secretions.