Download - Adaptive immunity
THE IMMUNE SYSTEM
•Defense Mechanisms
Adaptive Immunity
• Immunity that an organism develops during lifetime
• Develops after exposure to antigens• Invovles the activity of lymphocytes• Includes 3rd line of defense
Adaptive Immunity (Specific immunity)
• Specificity
• Memory
• Ability to distinguish b/w self vs non-self
• T and B cell
Types of Adaptive Immunity
1. Antibody-Mediated Immunity (AMI) or Humoral Immunity– B lymphocytes
2. Cell-Mediated Immunity (CMI) or Cellular Immunity– T lymphocytes
Note: B and T cells ……..blood, lymph, lymphoid tissues such as spleen, lymph nodes etc.
•Lymphocyte Formation
CHECKPOINT
• 1. What are the two main types of lymphocytes?
• 2. What is an antigen? Name some examples.
Cell-Mediated Immune Response
• T cells
• Immune resoponse to infected cells( viruses, bacteria and parasites (Pathogens) within cells)
• Defense against cancer and transplant cells
•Chapter 21, Immune System •8
T-Lymphocytes
• Helper T cells – secrete CYTOKINES help B cells Tc cells to divide• Cytotoxic T cells (killer T cells) Kill infected body cells• Memory T cells remain in body
How do T cells know a cell is infected?
• Infected cells digest some pathogens and MHC proteins carry pieces to cell surface
• Antigen Presenting Cell (APC)• Alerts Helper T cells
•MHC proteins displaying
foreign antigensinfectedcell
•T cell with antigen receptors
•TH cell
•Chapter 21, Immune System •11
• MHC proteins,mark a cell as self
• The two classes of MHC proteins are:– Class I MHC proteins – found on virtually all body cells
– Class II MHC proteins – found on certain cells in the immune response
MHC Proteins
Macrophages
Antigen-Presenting Cells
– B cells– Dendritic cells– macrophages
Helper T Cells (TH)
• bind to other white blood cells that have previously encountered an antigen– stimulate proliferation of other T cells– Stimulate B cells that have already become bound
to antigen
• Without TH, there is no immune response
•Chapter 21, Immune System •14
The central role of Helper T Cells (Boss)
•Chapter 21, Immune System •15•Figure 21.17a
Cytotoxic T Cell (Tc)
• Destroys infected body cells– binds to target cell– secretes perforin protein
• punctures cell membrane of infected cell– apoptosis
•Chapter 21, Immune System •16
Cytotoxic T cells
•Killer T cellbinds to
infected cell
• Destroys infected body cells– binds to target cell– secretes perforin protein
• punctures cell membrane of infected cell– apoptosis
•infected cell•destroyed
•Cytotoxic T cell
•1
•Accessoryprotein
•Class I MHCmolecule
•Infectedcell
•Antigenreceptor
•Antigenfragment
•Cytotoxic T cell
•1 •2
•Accessoryprotein
•Class I MHCmolecule
•Infectedcell
•Antigenreceptor
•Antigenfragment
•Perforin
•Pore
•Gran-zymes
The killing action ofcytoxic T cells on an infected host
cell.
•Cytotoxic T cell
•3•1 •2
•Accessoryprotein
•Class I MHCmolecule
•Infectedcell
•Antigenreceptor
•Antigenfragment
•Perforin
•Pore
•Gran-zymes
•ReleasedcytotoxicT cell
•Dyinginfected cell
Figure 23.11 (1 of 2)
CMI
• Human Immunodeficiency Virus– virus infects and destroys helper T cells
• helper T cells don’t activate rest of immune system: killer T cells & B cells
• AIDS: Acquired ImmunoDeficiency Syndrome– infections by opportunistic
diseases– death usually from – “opportunistic” infections
• pneumonia, cancers
HIV & AIDS
•HIV infected T cell
ANTIBODY-MEDIATED (HUMORAL) IMMUNITY
• targets extracellular microorganisms (Bacteria and viruses circulating in the blood)
• B-lymphocytes (B cells)………. Antibodies • Antibodies… extracellular fluids and surface of B
cells
•Pathogen
•1
•Antigen-presentingcell •Antigen
fragment
•Class IIMHC
molecule
•Antigenreceptor
•Accessoryprotein
•Helper T cell
•Pathogen
•1 •2
•Antigen-presentingcell •Antigen
fragment
•Class IIMHC
molecule
•Antigenreceptor
•Accessoryprotein
•Helper T cell
•B cell
•Cytokines
•Activatedhelper T cell
•Pathogen
•3•1 •2
•Antigen-presentingcell •Antigen
fragment
•Class IIMHC
molecule
•Antigenreceptor
•Accessoryprotein
•Helper T cell
•B cell
•Cytokines
•Activatedhelper T cell
•Memory B cells
•Plasma cells•Secretedantibodies
Antibody-mediated (humoral) immunity = AMI
• 1- Macrophages phagocytize a pathogen and present an antigen to a matching helper-T cell
• 2- At the same time, some pathogens contact B-cells matching the pathogen’s antigens
• The helper-T cells multiply, secrete lymphokines which stimulate the B-cells to multiply and specialize into plasma cells
• The plasma cells secretes antibodies
The Nature of Antibodies
• Globular proteins called immunoglobulins• Basic antibody structure has 4 polypeptide chains
– 2 identical light chains– 2 identical heavy chains
• Regions of heavy and light chains– Variable– Constant
Antibody Molecule
•antigen binding sites
•antigen
•light chains •heavy chains
•Immunoglobin ClassesImmunoglobin Classes
• IgM• 1st response to antigen• Can’t cross placenta
• IgG• Most common form• Crosses placenta
(passive immunity to fetus)
• IgA• Secreted from mucus
membranes• In colostrum
• IgD• B cell activation• Can’t cross placenta
• IgE• Histamine
reactions and allergies (mast cells, basophils)
First and second exposures to a pathogen
Role of the antibodies
•The classical compliment pathway, resulting in lysis of a target cell
Types of Immunity
• Active ImmunityNatural active immunity - acquired due to infectionArtificial active immunity – vaccination
• Passive ImmunityNatural passive immunity• placenta to the fetus• Colostrum
Artificial passive immunity• Injection of immune serum
Types of Acquired Immunity
Immune system Disorders• Allergies• Allergies are exaggerated (hypersensitive) responses to
antigens called allergens
• Allergens…. antigens
•© 2011 Pearson Education, Inc.
•41
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