Slide 1AntigensImmunity and Immune ResponseSlide 4The Immune System: Origin and DevelopmentSlide 6The Immune SystemImmunity and the Immune Response SystemSlide 9Slide 10Classes of Antibodies (Immunoghlobulins)Humoral (Antibody-mediated) Immune Response to AntigenHumoral Immune Response to Different AntigensHumoral or B-Cell Mediated Immune ResponseImmunoglobulin G (IgG) and Reaction with AntigenEffect of Antigen Size on Humoral ImmunityFate of Antigen-Antibody ComplexesCell-Mediated Immunity and T CellsCell Mediated Immune System: T lymphocytesT Cells and their FunctionsAutoimmune diseaseInteractions of the Components of The Immune ResponseSlide 23Slide 24Slide 25Immunity, Immune System and Immune ResponseEnvr 421Mark D. SobseyAntigensAny foreign substance that elicits an immune response when introduced into the tissues of a susceptible animal and capable of combining with the specific antibodies formed. Generally high molecular weight Typically, proteins or polysaccharides. Polypeptides, lipids, nucleic acids and many other materials also can also function as antigensMicrobes are antigenic and they contain and produce many antigens Antigens have specific sites that bind to antibodies called “epitopes”Immunity and Immune ResponseMade up of two cellular systems: •Humoral or circulating antibody system–B cells •Cell mediated immunity–T cellsImmunity and Immune Response•Immune system identifies antigens (foreign proteins or polysaccharides) –Components of microbes or their partially degraded byproducts and –Other foreign proteins and polysaccharides (including nucleic acids)•Host (human or animal) antigens not made by the individual are also antigens–Result: in graft, transplant rejectionThe Immune System: Origin and Development•Human immune system begins to develop in the embryo. •Starts with hematopoietic (from Greek, "blood-making") stem cells. •Stem cells differentiate into major cells in the immune system –granulocytes, monocytes, and lymphocytes•Stems cells also differentiate into cells in the blood that are not involved in immune function, such as erythrocytes (red blood cells) and megakaryocytes (for blood clotting). •Stem cells continue to be produced and differentiate throughout ones lifetime.Biological Components of Human Immune SystemThe Immune System (AKA: polymorphonuclear leucocytes)• (neutrophils, eosinophils and basophils)(Cell-mediated immunity)(Antibody-mediated immunity)(Red blood cell)(Non-specific cells responding to antgens and allergens)Immunity and the Immune Response SystemImmunity and the Immune Response SystemClonal Selection of B Cells is Due to Antigenic StimulationClasses of Antibodies (Immunoghlobulins)Humoral (Antibody-mediated) Immune Response to Antigen•First-time Antigen Exposure: 1o Response–Several day lag, then antibody becomes detectable. –Antibody is IgM class–After a short time, antibody level declines•Later Re-exposure to Same Antigen: 2o (anamnestic) response–more rapid Ab appearance and in greater amount. –IgG class of antibody–Remains detectable for months, years or lifetime.Humoral Immune Response to Different Antigens•First exposure to antigen "A”:–Begin to make low levels of antibody after several days•Second exposure to antigen "A”:–produces a much faster response, and–Several orders of magnitude higher levels of antibody. –Ability of antibody to bind antigen also increases dramatically in the secondary response. •Injecting a new antigen "B” + "A" –Elicits only a primary response–Shows that a memory or prior exposure is required for the accelerated response.Humoral or B-Cell Mediated Immune ResponseProduces secreted antibodies (proteins)•Bind to antigens and identify the antigen complex for destruction. •Antibodies act on antigens in the serum and lymph •B-cell produced antibodies may be–attached to B-cell membranes or –Free in the serum and lymph. •Each B lymphocyte makes a unique antibody molecule (immunoglobulin or Ig) •Over a million different B lymphocytes are produced in each individual–So, each individual can recognize more than a million different antigensImmunoglobulin G (IgG) and Reaction with Antigen IgG antibody molecule–Composed of 2 copies of 2 different proteins– Two copies of a heavy chain•>400 amino acids long –Two copies of a light chain - •>200 amino acids long•Each IgG antibody molecule can bind 2 antigens at one time –A single antibody molecule can bind to 2 antigens (e.g., viruses, bacateria or other particle), which leads to clumpingEffect of Antigen Size on Humoral ImmunityFate of Antigen-Antibody Complexes•Ag-Ab complexes engulfed into the B-cell and partially digested •Antigen is displayed on the B-cell surface by a special receptor protein (MHC II) fo recognition by helper T-cells •B-cell is activated by the helper T-cell to divide and produce secreted antibodies–Abs circulate in the serum and lymph •Some B-cells become memory cells to produce antibody at a low rate for a long time (long term immunity)–They respond quickly when the antigen is encountered again– the response is regulated by a class of T-cells called suppressor T-cellsCell-Mediated Immunity and T Cells•T cell receptors are cell surface receptors that bind non-self substances on the surface of other cells• Major histocompatibility complex (MHC) proteins protrude from the surfaces of most cells in mammals–They help to distinguish self from nonself –They coordinate interactions among lymphocytes and macrophages• Cytokines are soluble signal proteins released by T cells–They bind and alter the behavior of their target cellsCell Mediated Immune System: T lymphocytes•T-cells mature in the thymus (thus the name T-cell) •Act on antigens appearing on the surface of individual cells.•Over a million different kinds of T-cells–Each produces a different receptor in the cell membrane–Each receptor is composed of 1 molecule each of two different proteins–Each receptor binds a specific antigen but has only one binding site–Receptor only recognizes antigens which are "presented" to it within another membrane protein of the MHC type (major histocompatibility complex)•Recognizes specific antigens bound to the antigen- presenting structures on the surface of the presenting cell.•Recognizes antigens presented by B-cells, macrophages, or any other cell typeT Cells and their Functions•Have a specific receptor