BIO244Chapter17Notes

BIO244Chapter17Notes - Adaptive Immunity: Specific...

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Unformatted text preview: Adaptive Immunity: Specific Defenses of the Host (Chapter 17) Immunity = resistance: defense against foreign material Innate immunity = defenses that are always present to provide instant protection against infection Adaptive immunity = induced, adapts to a specific foreign substance, acquired memory of the infection Antigens = substances that provoke an immune response, immunogenic molecules Lecture Materials for Amy Warenda Czura, Ph.D. Suffolk County Community College Eastern Campus Dual Nature of Adaptive Immune Response: 1. Humoral / Antibody-Mediated Immunity -involves antibodies produced by B cells to confer immunity -best against bacteria, toxins, and virus that are free in body fluids 2. Cell-Mediated Immunity -involves T cells that act against foreign organisms or tissues -involves cytokines & cytotoxicity P r im a r y S o u r c e f o r fi g u r e s a n d c o n te n t: T o r to r a , G .J . M ic r o b io lo g y A n I n tr o d u c tio n 8 th , 9 th , 1 0 th e d . S a n F r a n c is c o : P e a r s o n B e n ja m in C u m m in g s , 2 0 0 4 , 2 0 0 7 , 2 0 1 0 . -works best on bacteria- or virus-infected cells, fungi, protozoa, tissue grafts and cancer 1. Naturally Acquired Active Immunity -everyday exposure to antigens & disease -development of B and T cell responses & memory, immunity may be life long 2. Naturally Acquired Passive Immunity -transfer of antibodies from mother to fetus or infant across placenta or in milk -immunity lasts as long as antibodies, weeks to months 3. Artificially Acquired Active Immunity -vaccination / immunization: forced introduction of nonvirulent antigens -development of B and/or T cell responses & memory, immunity may be life long 4. Artificially Acquired Passive Immunity -injection of preformed antibodies from people or animals, called antiserum -immunity lasts as long as antibodies, weeks to months Four Types of Adaptive Immunity: (on handout) Amy Warenda Czura, Ph.D. 1 SCCC BIO244 Chapter 17 Lecture Notes Antigens: -determine self vs. non-self -non-self provokes immune response -located on the surface of cells: capsules, walls, flagella, fimbriae, pentons, spikes, etc., or toxin molecules -most are proteins or large polysaccharides -the specific antigenic compound recognized by lymphocytes or antibodies is called the epitope / antigenic determinant -lymphocytes have receptors to recognize and specifically bind to the epitope -antibodies have specific antigen-binding sites -a single pathogen or antigen can have hundreds of different epitopes / antigenic determinants on its surface, each of which would be recognized and bound by a different antibody or lymphocyte Antibodies / Immunoglobulins -special protein produced by plasma cells (B cells) that will recognize and bind to its specific epitope of an antigen via its antigen binding sites Classes of Antibodies/Immunoglobulins IgG antibodies (on handout) • Monomer -antibodies recognize and bind to specific shape of antigen’s epitope -antibodies have great specificity -affinity = strength of bond between antigen and antibody -each has minimum of 2 antigen binding sites: both recognize same epitope (antigen) Antibody Molecule Structure: (on handout) • • • • • 80% of serum antibodies Produced on second+ exposures In blood, lymph Can enter tissues, cross placenta Fix complement, enhance phagocytosis, neutralize toxins & viruses, protects fetus & newborn, antiserum IgG IgM antibodies • • • • • Pentamer 5-10% of serum antibodies Produced only on first exposure In blood, lymph, on B cells Fix complement, agglutinates antigens IgA IgA antibodies • • • • IgM Dimer 10-15% of serum antibodies In secretions Mucosal protection IgD IgD antibodies • • • • Monomer 0.2% of serum antibodies Surface receptor on B cells Initiate humoral immune response by B cells IgE antibodies • • • • Amy Warenda Czura, Ph.D. 2 Monomer 0.002% of serum antibodies Surface receptor on mast cells and basophils Inflammation, allergic reactions; lysis of parasitic worms IgE SCCC BIO244 Chapter 17 Lecture Notes Activation and Clonal Selection of B cells B cells and Humoral Immunity -B cells produce antibodies = humoral / antibody-mediated immunity -B cells arise from stem cells in bone marrow -when mature, migrate to lymphoid tissue -wait to recognize and bind to antigen to be stimulated to produce antibodies T-independent Antigen Activation of B cells by clonal selection: -each B cells produces only one antibody against one antigen/epitope -recognizes antigen/epitope via IgD receptor on cell surface -when activated it will divide to produce clones (on handout) ( E p ito p e te n d s to b e p o ly s a c c h a r id e , p r o d u c e s w e a k e r im m u n e r e s p o n s e th a n T - d e p e n d e n t A n tig e n ) 1 . I g D a n tib o d y r e c e p to r o n B c e ll b in d s its s p e c ifi c a n tig e n /e p ito p e 2 . B c e ll is a c tiv a te d a n d u n d e r g o e s c lo n a l s e le c tio n : th e B c e ll p r o lif e r a te s a n d d if f e r e n tia te s i n to tw o ty p e s o f c e ll p o p u la tio n s : M e m o r y B c e lls a n d P la s m a C e lls 3 . P la s m a c e lls s e c r e te a n tib o d ie s s p e c ifi c f o r th e o r ig in a l e p ito p e ( 2 0 0 0 a n tib o d y m o le c u le s p e r s e c o n d ) f o r 3 - 5 d a y s [ T im e f r o m in itia l a n tig e n b in d in g to a n tib o d ie s a p p e a r in g in th e b lo o d is 7 - 1 0 d a y s ] A n tib o d ie s b in d to f r e e a n tig e n s . 4 . U p o n s e c o n d e x p o s u r e to th e s a m e a n tig e n /e p ito p e , m e m o r y c e lls b in d a n tig e n a n d a r e t r ig g e r e d to d if f e r e n tia te in to p la s m a c e lls a n d s e c r e te a n tib o d ie s . [ T im e f r o m in itia l a n tig e n b in d in g to a n tib o d ie s a p p e a r in g in th e b lo o d is 2 - 5 d a y s ] M e m o r y c e lls = lo n g te r m im m u n ity Results of Antigen-Antibody Binding:(handout) 1. 6. MAC 5. 2. Primary Response: -initial exposure to antigen results in IgM production -peak titer 10-17 days -peak titer of antibodies low Secondary/Memory Response: -second and subsequent exposure results in IgG production -peak titer 2-7 days -much higher peak titer of antibodies Function of Antibodies antigen-antibody complex = antibody bound by its antigen-binding sites to the epitope Amy Warenda Czura, Ph.D. Antigen bound to IgE on Mast cells triggers histamine release and 3. 4. Macrophages Eosinophils NK cells 3 SCCC BIO244 Chapter 17 Lecture Notes T cells and Cell-Mediated Immunity -requires coordinated activity of specialized cells that must communicate Communication chemicals = cytokines -chemical messengers used within immune system (proteins or glycoproteins) -many kinds, each has specific message Cells = T cells -originate from stem cells in bone marrow but mature in thymus, travel to blood & lymph -each only recognizes one antigen -when it binds to antigen, will undergo clonal selection to produce effector and memory cells -effector cells: attack foreign cells or stimulate other defense cells via cytokines -memory cells: rapid response upon second exposure, long term immunity -T cells do not bind free antigen: must be on cell surface in association with molecules of the major histocompatibility complex (MHC) (on handout) Class I MHC I n f e c te d c e ll C la s s I M H C is f o u n d o n a ll c e ll ty p e s a n d d is p la y s a ll a n tig e n s th a t a r e p r e s e n t in a c e ll, b o th s e lf a n d n o n - s e lf . C la s s I I M H C is f o u n d o n ly o n A P C s a n d o n ly d is p la y s a n tig e n s th a t h a v e b e e n e n d o c y to s e d Class II MHC A n tig e n P r e s e n tin g C e ll Types of T cells: 1. TH (Helper T cells) / CD4 Cells -activated by antigen in Class II MHC -respond by secreting cytokines to influence other immune cells Activation of Helper T Cells (on handout) C la s s I I TH1 A. TH1: activate cells related to cellmediated immunity (TC and Macrophages) B. TH2: activate B cells to make antibodies (T-dependent antigens) Amy Warenda Czura, Ph.D. D e f e n s e a g a in s t in tr a c e llu la r p a th o g e n s 4 TH2 D e f e n s e a g a in s t f r e e p a th o g e n s SCCC BIO244 Chapter 17 Lecture Notes 2. TC (Cytotoxic T cells) / CD8 Cells -activated by antigen in Class I MHC -respond by secreting perforin and lysing the target cell: -this usually requires pre-activation of the TC by cytokines produced by a TH1 cell Activation of Cytotoxic T Cells (on handout) Natural Killer Cells (NK cells) -not immunologically specific -attack any abnormal antigen on eukaryotic cells: virus-infected, cancer, large parasites -attack cells lacking proper class I MHC -lyse target cell by releasing perforins to disrupt membrane Inter-relationship of Cell-Mediated and Antibody-Mediated Immunity T-dependent antigens: -more common than T-independent antigens -protein epitopes -require TH2 cells to signal B cells to produce antibodies (on handout) 3. TS (Suppressor T cells) aka Treg (Regulatory T cells) -regulate the immune response -prevent autoimmunity -inhibit T and B cell activity when antigen levels decline T-dependent antigens: Most activity of the immune system requires cytokines produced by T Helper cells T-independent antigens: (previous notes) -activate B cell directly -less common -antigens: polysaccharides, lipopolysaccharides -weaker immune response Amy Warenda Czura, Ph.D. Most activities of B and T cells function to enhance non-specific defenses / innate immunity (on handout) 5 SCCC BIO244 Chapter 17 Lecture Notes Body Defense Summary N o n - s p e c ifi c d e f e n s e s a n d th e im m u n e r e s p o n s e a r e in te g r a te d : b o th f u n c tio n to g e th e r f o r o v e r a ll d e f e n s e D e f e n s e a g a in s t in tr a c e llu la r p a th o g e n s Amy Warenda Czura, Ph.D. D e f e n s e a g a in s t f r e e p a th o g e n s 6 SCCC BIO244 Chapter 17 Lecture Notes ...
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