Bio WW3

• The adaptive immune system has four major characteristics: diversity of lymphocytes and receptors, self-tolerance, B and T cells proliferate after activation, and immunological memory.
• Immune System: Compare nonspecific and specific defenses, explain how the various nonspecific defenses function in defending the body, and describe how various specific defenses work: humoral vs cell-mediated immunity.
• White blood cells are the key players in immune defense.
• Local Inflammatory Response: Adaptive immunity defends against infection of body fluids and body cells.
• Humoral immune response: antibodies help neutralize or eliminate toxins and pathogens in the blood and lymph.
• Cell-mediated immune response: specialized T cells destroy affected host cells.
• In adaptive immunity, receptors provide pathogen-specific recognition.
• The adaptive response relies on two types of lymphocytes, or white blood cells.
• Lymphocytes that mature in the thymus above the heart are called T cells, and those that mature in bone marrow are called B cells.
• Antigens are substances that can elicit a response from a B or T cell.
• Exposure to the pathogen activates B and T cells with antigen receptors specific for parts of that pathogen.
• The small accessible part of an antigen that binds to an antigen receptor is called an epitope.
• B cells and T cells have receptor proteins that can bind to foreign molecules.
• Each individual lymphocyte is specialized to recognize a specific type of molecule.
• Two types of clones are produced: short-lived activated effector cells that act immediately against the antigen and long-lived memory cells that can give rise to effector cells if the same antigen is encountered again.
• Proliferation of B cells and T cells involves the antigen fragment binding to the antigen receptor on the surface of the host cell.
• Once activated, a B or T cell undergoes multiple cell divisions, a process called clonal selection.
• Cell-mediated immune response involves the antigen fragment binding to the antigen receptor on the surface of the host cell.
• In the secondary immune response, memory cells facilitate a faster, more efficient response.
• The killing action of cytotoxic T cells on an infected host cell involves the antigen fragment binding to the antibody on the surface of the host cell.
• The first exposure to a specific antigen represents the primary immune response, during which selected B and T cells give rise to their effector forms.
• Antigen recognition by a T cell involves the T cell antigen receptor binding to the antigen fragment, which is displayed on the surface of the host cell.
• Activation of a B cell in the humoral immune response involves the antigen fragment binding to the antibody on the surface of the host cell.
• Immunological memory is responsible for long-term protections against diseases, due to either a prior infection or vaccination.
• Humoral (antibody-mediated) immune response involves the antigen fragment binding to the antibody on the surface of the host cell.
• Binding of a B cell antigen receptor to an antigen is an early step in B cell activation.
• This gives rise to cells that secrete a soluble form of the protein called an antibody or immunoglobulin (Ig).
• Secreted antibodies are similar to B cell receptors but lack transmembrane regions that anchor receptors in the plasma membrane.
• T cells bind to antigen fragments displayed or presented on a host cell.
• These antigen fragments are bound to cell-surface proteins called MHC molecules.
• MHC (major histocompatibility complex) molecules are host proteins that display the antigen fragments on the cell surface.