B cells produce antibodies and secrete them into the blood and tissue fluid.Antibodies are soluble in blood and tissue fluid. The action of antibodies is called humoral immunity.There are about 10 million different types of B cell each with a different receptor on its cell surface. Each B-cell receptor responds to a specific antigen.Antigens can be proteins on the surface of pathogens or abnormal cell and can also be toxins produced by bacteria.When the B cell receptor attaches to the antigen, the antigen enters the cell by endocytosis and is processed by the B cell.The B cell becomes antigen-presenting and T-helper cells that recognise the antigens bind to the antigens on the surface of the B cell and become activated.Activated T helper cell then stimulate the B cells to divide by mitosis, This is called clonal selection.Several B cells may recognise different antigens. Each clone differentiates into B plasma cells and B memory cells.B plasma cells secrete antibodies into the blood plasma and tissue fluid.Memory cells are responsible for the secondary immune response and circulate around the body ready for a future encounter with the pathogen.
