Introduction. Skin. The Immune System. Chapter 51

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1 The Immune System Chapter 51 Introduction Vertebrates have three levels of defenses -1. The Integumentary System -Skin and mucous membranes provide first line of defense -2. Nonspecific (innate) Immune System -Acts very rapidly after onset of infection -3. Specific Immune System -Eliminates microbes that escaped the second line of defense 2 Skin The skin is the largest organ of the body -Provides a nearly impenetrable barrier, reinforced with chemical weapons -Oil & sweat glands give skin a ph of 3-5 -Lysozyme breaks bacterial cell walls -Also contains many normal flora -Non-pathogenic microorganisms that out-compete pathogenic ones 3 1

2 Mucosal Epithelial Surfaces The digestive, respiratory and urogenital tracts are lined by mucous membranes -Cells secrete mucus which traps microbes Digestive tract -Salivary lysozyme; acidic stomach Respiratory tract -Ciliary action Urogenital tract -Acidic urine 4 Nonspecific Immunity The nonspecific or innate immune system consists of cellular and chemical devices that respond to any microbial infection -The response is quite rapid Among the most important defenses are three types of leukocytes (white blood cells) 5 Leukocytes Macrophages -Large, irregularly shaped cells -Kill microbes by phagocytosis -Mature from monocytes that enter tissues from the blood 6 2

3 Leukocytes Neutrophils -The most abundant circulating leukocytes -First to appear at site of damage/infection -Kill microbes by phagocytosis Natural killer (NK) cells -Destroy pathogen-infected and cancer cells by programmed cell death or apoptosis -Produce perforins and granzymes 7 The Inflammatory Response Inflammation involves several body systems -Injured cells release chemical alarms, including histamine and prostaglandins -Cause nearby blood vessels to dilate and increase in permeability -Promote phagocyte accumulation -Hallmark signs = Redness, warmth, swelling, pain, and potential loss of function 8 Complement The complement system consists of about 30 different proteins that circulate in the blood in an inactive form -Upon pathogen encounter, a cascade of activation occurs -Some proteins aggregate to form a membrane attack complex (MAC) on surface of pathogen 9 3

4 Complement Other functions of complement proteins -C3b coats surface of invading pathogens, thereby enhancing their phagocytosis -Some stimulate the release of histamine from mast cells and basophils -Some attract more phagocytes to the area of infection 10 Interferon Interferons (IFN) are proteins that play a key role in body defense -Three major types: IFN-α, IFN-β, IFN-γ -IFN-α and IFN-β are produced by almost all body cells in response to viral infection -Induce degradation of viral RNA -IFN-γ is produced only by T-lymphocytes and natural killer cells -Protects from infection and cancer 11 The Specific Immune System The scientific study of immunity began with Edward Jenner in Observed that milkmaids who had cowpox rarely experienced smallpox -Inoculated individuals with fluid from cowpox vesicles to protect them from smallpox -Vaccination 12 4

5 The Specific Immune System The four characteristics of the specific, or adaptive, immune response are: -1. Specificity -2. Diversity -3. Memory -4. Ability to distinguish self from non-self 13 Antigens An antigen is a molecule that provokes a specific immune response -May be components of microorganisms or proteins/glycoproteins found on surface of red blood cells or transplanted tissue cells 14 Lymphocytes Lymphocytes are leukocytes with surface receptors for antigenic determinants -Direct an immune response against either the antigen or the cell that carries it When a naïve lymphocyte binds a specific antigen for the first time, it gets activated by a process called clonal selection -Produces a clone of cells: some respond immediately, others are memory cells 15 5

6 Lymphocytes B lymphocytes or B cells -Respond to antigens by secreting antibodies or immunoglobulins (Ig) -Participate in humoral immunity T lymphocytes or T cells -Regulate other immune cells or directly attack cells that carry specific antigens -Participate in cell-mediated immunity 16 Acquisition of Specific Immunity Immunity can be acquired in two ways -Active immunity results from activation of an individual s own lymphocytes -Pathogen infection or vaccination -Passive immunity results from obtaining another individual s antibodies -Transfer of maternal antibodies across placenta 17 T Cells T lymphocytes are of two types: -Cytotoxic T cells (T c ) -CD8 + cells -Helper T cells (T H ) -CD4 + cells -Distinguished by type of MHC markers recognized and roles after activation 18 6

7 T Cells In humans, the MHC complex is also termed human leukocyte antigens (HLAs) -Markers that distinguish self from nonself 19 T Cells Cytotoxic T cells -Clonal expansion and differentiation into activated cells and memory cells -Activated cells induce apoptosis in cells with same specificity as first cell -Likely a viral-infected or cancer cell 20 T Cells Helper T cells -Activated T H cell gives rise to a clone of T H cells including both effector cells and memory cells -Most effector T H cells leave the lymphoid organs and circulate around the body -Secrete proteins called cytokines -Promote humoral and cell-mediated immune responses 21 7

8 B Cells Humoral immunity begins when naïve B cells in secondary lymph organs meet antigens -B cells are activated when their surface Igs bind to a specific epitope on an antigen -T H cytokines may also be required -Activation results in clonal expansion and differentiation into plasma and memory cells -Plasma cells produce soluble antibodies against the same epitope 22 Immunoglobulins An immunoglobulin consists of two identical short polypeptides, light chains, and two identical longer polypeptides, heavy chains -Four chains are held by disulfide bonds, forming a Y-shaped molecule -Fab regions = Two arms -Fc region = Stem 23 Immunoglobulins Each chain has a variable region (amino acid sequence differs between Igs) and a constant region -The variable regions fold together to form a cleft, the antigen-binding site Each Ig can bind two identical epitopes -Allows formation of antigen-antibody complexes -Indeed, Igs can agglutinate, precipitate or neutralize antigens 24 8

9 Immunoglobulins There are five classes of immunoglobulins -IgM = First type of antibody produced during an immune response -Monomer on B cells, but secreted as pentamer -IgD = Present on mature naïve B cells -Not secreted in normal situations 25 Immunoglobulins -IgG = Major form of antibody in blood -Main component of secondary response -Can cross placenta -IgA = Major form of antibody in secretions -Usually produced as a dimer -Can pass to nursing infant in mom s milk -IgE = Present at very low levels in blood -Plays a role in allergic reactions

10 Immune Responses The first encounter with a foreign antigen is called the primary immune response -Only few B or T cells can recognize antigen The second encounter is called the secondary immune response -This time there is a large clone of memory cells that can recognize the antigen -Immune response is more effective

Name (print) Name (signature) Period. (Total 30 points)

Name (print) Name (signature) Period. (Total 30 points) AP Biology Worksheet Chapter 43 The Immune System Lambdin April 4, 2011 Due Date: Thurs. April 7, 2011 You may use the following: Text Notes Power point Internet One other person in class "On my honor,