Post on 12-Jan-2016
Lecture 14
Immunology:
Adaptive Immunity
Principles of Immunity• Naturally Acquired Immunity- happens
through normal events• Artificially Acquired Immunity- by
immunization• Active Immunity- result of an immune
response in an individual exposed to antigen
• Passive Immunity- occurs naturally during pregnancy; or antibodies from one person transferred to another
• Innate Immunity- Immunity that we are born with
Figure 17.1
Adaptive Immunity
• Different from Innate Immunity
• Matures throughout life
• Develops specific immune response as invaders are encountered
• Has a “memory”
• Must discriminate between self and dangerous (non-self)
• Very complex system
Adaptive Immunity
• Four important attributes:• Specificity- immune system responds
specifically to epitopes
• Tolerance of “self”- Immune system does not respond to “self”
• Minimal “self” damage- do not damage “self”
• Immunologic Memory- Once exposed will not get sick with same disease again
Overview of Adaptive Immunity
• Uses two basic strategies
1. Humoral Immunity
- works to eliminate antigens that are extracellular
1. Cellular Immunity
- deals with antigens within host cell
Humoral Immunity
Overview of Humoral Immune Response
• Mediated by B-lymphocytes or B-cells
• Encounter antigen- differentiate and proliferate into plasma cells and memory B cells
• Plasma cells make Y-shaped molecules called antibodies
• Antibodies bind to antigens, providing protection to host
Antibodies
• Globulin protein molecules- also called Immunoglobulins
• Secreted by B-cells
• Y-shaped
• 5 different classes:– IgM, IgG, IgA, IgE, IgD
Figure 17.3 - Overview
Table 17.1
Immunoglobulin M (IgM)
• First class produced during primary immune response to antigen
• It is in pentamer form
• Large- does not cross from blood to tissues
Immunoglobulin G (IgG)
• 80-85% of total Ig’s in people over age 2• Provides longest term protection of all
antibodies• First and most abundant Ig, during
secondary response• Can cross placenta from mother to fetus-
helps to protect fetus and new-born• Also present in colostrum- first breast-milk
produced
Immunoglobulin A (IgA)
• Important in mucosal immunity• In breast milk- protects infants from
intestinal pathogens
Immunoglobulin D (IgD)- Accounts for less than 1% of Ig’s- Involved in development and maturation of
antibody response
Immunoglobulin E (IgE)
• Barely detectible in blood
• Bound tightly to basophils and mast cells
• Bound IgE, allows these cells to detect and respond to antigens
• These cells release histamine, cytokines, and other chemicals that contribute to immune response
Allergies
• Basophils and mast cells release their chemicals when IgE binds to normally harmless material such as pollens
• Leads to immediate reaction- coughing, sneezing, and muscular contractions
• Response can be life threatening
Primary and Secondary Responses of Antibodies
Protective Outcomes of Antibody-Antigen binding
A. Viral Inhibition: virus preventing it from attaching to cell
B. Neutralization: make toxins unable to bind to cells
C. Opsonization: antibodies bind to antigen and facilitate attachment of phagocytic cells
D. and E. Agglutination and Precipitation: antibodies bind to antigen and get them into clumps, then one big “mouthful” for phagocyte
F. Phagocytosis: Fc portion of antibody encourages phagocytosis
Complement Activation: binding of antigen to antibody can trigger one pathway of complement cascade
B-cells and Antibody Response
• B-cell receptor binds to antigen
• One of two things happen:– B-cell needs confirmation by T-cell to begin
responding– B-cell does not need confirmation by T-cell to
begin responding
When B-cell does not need confirmation from T-cell
• B-cell receptors bind epitopes
• B-cells respond by proliferating, producing antibody and differentiating into memory B-cells
Fi When B-cell needs confirmation from T-cell gure 16.9
Cellular Immunity
Overview of Cellular Immunity
• Mediated by T lymphocytes or T-cells
• Has receptor similar to B-cells
• Antigen must be presented to it by another cell
• Two types:– T-cytotoxic cells- destroy infected cells– T-helper cells- activate macrophages
T-cells: Antigen Recognition and Response
• Have multiple copies of receptor on surface that recognizes specific antigen
• DO NOT produce antibody• DOES NOT interact with free antigen• Antigen must be presented by another
cell, by MHC • Two types of T-cells:
– T-cytotoxic– T-helper
Figure 16.15
T-cytotoxic cells
• Also called CD8 T cells
• Once activated, induce apoptosis in “self” cells infected with virus; destroy cancerous host cells
• Distinguish infected “self” cells, because these cells present peptides on surface in MHC class I molecule
Figure 17.10 - Overview
T-helper cells
• Also called CD4 T-cells
• Antigen presenting cells, present antigen to T-helper cells in MHC class II
• If recognize antigen presented as foreign, activate macrophages, release cytokines that recruit other cells of immune system, stimulate NK cells, activate B cells
Figure 17.9 - Overview (1 of 4)