Understandings:

• Every organism has unique molecules on the surface of its cells
• Pathogens can be species-specific although others can cross species barriers
• B lymphocytes are activated by T lymphocytes in mammals
• Activated B cells multiply to form clones of plasma cells and memory cells
• Plasma cells secrete antibodies
• Antibodies aid the destruction of pathogens
• White blood cells release histamine in response to allergens
• Histamine causes allergic symptoms
• Immunity depends on the persistance of memory cells
• Vaccines contain antigens that trigger immunity but do not cause the disease
• Fusion of a tumor cell with an antibody-producing cell creates a hybridoma cell
• Monoclonal antibodies are produced by hybridoma cells