What does the immune system help the body to do? What are the cells called that produce antibodies? How are lymphocytes produced? Describe the difference between lymphocytes that have not been stimulated by antigens and those that have. What are plasma cells and memory cells; what does each do in terms of helping the body fight infection?
The immune system in humans allows the body to fight disease by producing antibodies that are able to deactivate invading molecules, usually in the form of proteins or polysaccharides, called antigens. The cells that produce the antibodies are called plasma cells, a type of B lymphocyte found in blood, in lymph, and in the lymphoid tissue of the spleen, thymus, and lymph nodes. Lymphocytes arise from lymphoid stem cells which, in turn, arise from hemopoietic stem cells, the cells that produce all leukocytes as well as erythrocytes. Before antigen stimulation, B lymphocytes are small, metabolically inert cells that can circulate freely between lymph and blood vessels by moving through the gaps in the endothelial cells of the lymph and blood capillary walls. When stimulated by an antigen, the small, inactive B lymphocyte grows and begins cell division producing plasma cells and memory cells. Plasma cells secrete the antibodies that deactivate the invading antigens. Memory cells resemble exactly the original lymphocyte and, thus, make it possible for the body to
