An antigen is a substance that stimulates the formation of antibodies in the immune system.

Antigens are typically foreign substances that enter the body, such as bacteria, viruses, or other pathogens. They can also be non-living substances like toxins or proteins from allergens. When the immune system detects an antigen as foreign or potentially harmful, it triggers an immune response. This response includes the production of specific proteins called antibodies, which are designed to recognize and neutralize the antigen.

Antigens stimulate the formation of antibodies through a process known as antigen recognition. The immune system`s cells, such as B cells and T cells, recognize specific antigens and initiate the production of antibodies that specifically target and bind to those antigens. This immune response helps the body defend against infections and diseases caused by foreign substances.

To summarize, antigens are substances that stimulate the formation of antibodies in the immune system and are an important part of the body`s defense against pathogens and foreign substances. They do not destroy harmful bacteria, treat poisoning, or lower body temperature themselves; rather, they trigger an immune response that leads to the production of antibodies.