How do antigens trigger the immune response?

Antigens trigger the immune response by being recognised as foreign substances, which stimulates the production of specific antibodies.

Antigens are substances, often proteins, that are recognised by the immune system as foreign to the body. They can be found on the surface of pathogens such as bacteria, viruses, and fungi, or they can be toxins or other foreign substances. When an antigen enters the body, it is detected by the immune system, which triggers an immune response.

The immune response begins when the antigen is recognised by a type of white blood cell called a B lymphocyte, or B cell. Each B cell is programmed to recognise a specific antigen. When a B cell encounters its specific antigen, it binds to it, which stimulates the B cell to divide and produce clones of itself. These clones then differentiate into plasma cells and memory B cells.

Plasma cells are the body's antibody factories. They produce large amounts of specific antibodies that are released into the bloodstream. These antibodies bind to the antigens, marking them for destruction by other immune cells. This process is known as opsonisation. The antibodies can also neutralise toxins and prevent viruses from entering cells.

Memory B cells, on the other hand, do not produce antibodies immediately. Instead, they remain in the body for a long time, ready to respond quickly and forcefully if the same antigen is encountered again. This is the basis of immunity.

In addition to B cells, T cells are also involved in the immune response to antigens. Helper T cells stimulate B cells to produce antibodies and cytotoxic T cells kill infected cells directly. Regulatory T cells, meanwhile, help to control the immune response and prevent it from attacking the body's own cells.

In summary, antigens trigger the immune response by being recognised as foreign by B cells, which then produce specific antibodies. These antibodies mark the antigens for destruction, neutralise toxins, and prevent viruses from entering cells. Memory B cells provide long-term immunity, while T cells help to regulate the immune response and kill infected cells directly.