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Acquired and Humoral Immunity

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Acquired and Humoral Immunity Powered By Docstoc
					Dr Nirmala Limbu, MD
Assistant Professor
Department of Physiology
BPKIHS, Dharan
Learning Objectives
Introduction to humoral immunity
Development of immune system
Activation, proliferation & differentiation
 of B cells
Actions of antibodies
Primary vs. secondary response
Genetic basis of diversity in immune
 system
Acquired Immunity
  Specificity
  Memory
  Self/Non-self recognition

Introduction to Acquired Immunity- Humoral
(Antibody-mediated)
Mediated by circulated immunoglobin
 antibodies in γ-globulin fraction of plasma
 proteins
Introduction to Acquired Immunity- Humoral (Antibody-mediated) continue…….



Plasma cells (differentiated forms of B
 lymphocytes) – secrete Ig- activate
 complement system, attack & neutralize
 antigens
Major defense against bacteria, bacterial
 toxins & viruses that circulate in body fluids
Development of Immune system
Development of Immune system continue……

Before T cells leave thymus & B cells leave
 red bone marrow- they make distinctive
 proteins- insert into plasma membrane as
 antigen receptors, in T cells- CD4 & CD8
Development of Immune system continue……
Development of Immune system continue……

B Lymphocytes differ from T lymphocytes in
  2 ways:
- B lymphocyte secretes antibody develop
  reactivity against antigen instead of whole
  cell as in T cells
- B lymphocyte- greater diversity than T
  lymphocytes
Humoral Immunity (Antibody-mediated)
Activation, Proliferation & differentiation of
 B cells
Antigen can bind directly to appropriate
 receptors on B cells.
However, full antibody response requires
 that B cell contact with helper T cell
Depending on antigen, antibody synthesis is
 induced by thymus independent or thymus
 dependent mechanisms
Activation, Proliferation & differentiation of B cells continue…..
 Thymus independent antigen – do not
  require cooperation of T cells for activating
  B cells
• Antigens are mainly polysaccharides or
  lipopolysaccharides with repeating subunits
  (bacterial capsules).
• Weaker immune response than for T-
  dependent antigens.
• produce Ig M type of Antibody
Thymus dependent antigen- requires
  cooperation of T cells for B cell activation
Activation, Proliferation & differentiation of B cells continue…..


• Antigen is presented to specific B cells by
  Antigen presenting cells (macrophage)
Major Histocompatibility Complex (MHC)
Transmembrane glycoproteins located in
 plasma membrane of cells- “Self-Antigen”
MHC antigens are unique unless identical
 twins
2 classes- MHC I- present in all nucleated
 cells except RBC; MHC II- surface of APC, B
 cells
Activation, Proliferation & differentiation of B cells continue…..



MHC II appear on cell membrane only
 when cell is processing antigens.
Activation, Proliferation & differentiation of B cells continue…..

  B cells of particular clone- capable of
   secreting only one kind of antibody-
   identical in specificity in antigen receptor
   displayed by B cells that 1st responded to
   antigen
  Antibody forms antigen-antibody complex n
   initiate their actions.

  Immunoglobins
   Antibodies circulate in globin fraction of
    plasma - Immunoglobins
Immunoglobins continue……

Classes of antibodies- five general classes-
 IgM, IgG, IgA, IgD & IgE
Basic component of each- symmetric unit- 4
 polypeptide chains (2 heavy & 2 light)
Immunoglobins continue……




 Variable
 portion




Constant
portion
Action of Antibodies

                   Agglutination of
                   antigen-bearing
                   particles


                   Neutralization-blocks viral
                   binding sites, coats
                   bacteria and/or
                   opsonization
Action of Antibodies continues…..


                                    Precipitation of soluble
                                    antigens



                                     Opsonization- coat
                                     antigens




All these enhances phagocytosis
Action of Antibodies continues…..
Action of Antibodies continues…..

Activating complement system- amplify
 the action of antibodies
Primary vs. Secondary immune response
Primary vs. Secondary immune response continue…..
Primary vs. Secondary immune response continue…..
Genetic basis of diversity of immune system
Epitopes: Antigen Regions that Interact with
Antibodies
Genetic basis of diversity of immune system continue…..


Due to Genetic recombination
During preprocessing (T- & B- lymphocytes)-
 gene segments mix with one another in
 random combination & form one specific
 whole gene i.e. code for only single antigen
 specificity
Genetic basis of diversity of immune system continue…..

? Diverse antibody-
 during B cell
 development, coding
 region of each V, D & J
 regions are selected at
 random & recombine
 to form gene- produce
 specific variable
 portion
THE END…!!!

				
DOCUMENT INFO
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