I am particularly interested in the immune system because I love complexity. The immune system fights the body's invaders, attacks abnormally dividing and mutated cells, thus, preventing cancer, and influences brain activity. Further, the metabolites of the intestinal bacteria modulate the immune system, and immune cells and antibodies are used to develop sophisticated therapies that are summarized as immunotherapeutics.
The video shows two lymphocytes - one is an activated T-Helper Cell presenting a 'foreign' protein, which invaded the bloodstream, on its surface. The other is a B-Lymphocyte that produces antibodies that bind this protein at a particular part called 'antigen'. By binding to the antigen, the B-Lymphocyte is stimulated to divide and produce more antibodies. The antibodies bind the invaders, and accumulations are removed by the immune system's macrophages, the 'eating cells'. This is the 'specific' immune response of the immune system.