How many types of antigens are mentioned as part of the immune response?

The correct answer is based on the classification of antigens involved in the immune response, which typically consist of four main categories. These include:

1. Exogenous Antigens: These are foreign substances that enter the body from the outside, such as pathogens (bacteria, viruses, fungi) or toxins. They are recognized by immune cells and trigger an adaptive immune response.

2. Endogenous Antigens: These arise from within the body. They may be produced by normal cellular processes or as a result of infections (for example, viral proteins expressed on the surface of infected cells). The immune system can recognize these antigens when they are presented by Major Histocompatibility Complex (MHC) molecules on cell surfaces.

3. Autoantigens: These are the body’s own proteins that, under certain conditions, can be mistaken for foreign antigens by the immune system, potentially leading to autoimmune diseases.

4. Neoantigens: These are newly formed antigens that may arise from mutations in cancer cells, making them distinct from normal tissue antigens. They are important in oncology as they can be recognized by the immune system, providing targets for immunotherapy.

Each of these antigen types plays a crucial role in