cell surface antigen

A cell surface antigen is a substance that can trigger an immune response by activating lymphocytes, which are the body's infection-fighting white blood cells. These antigens can be foreign, originating from outside the body (like from viruses or bacteria), or they can be self-antigens, which are part of the body's own tissues.1

On the surface of antigens are specific regions called antigenic determinants. These determinants fit into complementary receptor molecules on lymphocytes, stimulating them to multiply and initiate an immune response, such as producing antibodies. This process is crucial for distinguishing between "self" and "non-self" to protect the body from foreign invaders. In some cases, like with blood groups, antigens on red blood cells can cause clumping when they react with specific antibodies.123