the immune system 1.the innate system 2.the adaptive system
TRANSCRIPT
The Immune SystemThe Immune System
1. The Innate System
2. The Adaptive System
The Innate Immune SystemThe Innate Immune System
“Nonspecific” system– Surface Barriers
– Cell and Chemical Responses
Innate Immunity: Surface BarriersInnate Immunity: Surface Barriers
Innate Immunity: Innate Immunity: Cell and Chemical DefensesCell and Chemical Defenses
• They do not target specific pathogens– They target abnormal or foreign cells
• Six categories:– Phagocytes– Natural killer (NK) cells– Inflammation response– The complement system– Interferons– Fever
PhagocytesPhagocytes
• Macrophages, neutrophils, eosinophils
1. Adherence and endocytosis2. Phagocytic endosome3. Lysosome fuses with endosome,
releases hydrolytic acids/enzymes4. Microbe is killed and digested5. Exocytosis
Natural Killer CellsNatural Killer Cells
• Lymphocytes that destroy tumor cells and cells infected with viruses
• Not phagocytes, instead release chemicals onto cell membranes– Cytolytic, perforin complexes
• The target cell lyses & nucleus disintegrates
• NK cells also release substances to stimulate inflammation
Inflammation Inflammation ResponseResponse
•Redness
•Increased Temperature
•Swelling
•Pain
The Complement SystemThe Complement System• > 20 plasma proteins • Activation triggers cascade
of chemical reactions• Molecular Complexes form:
– Membrane Attack Complex creates holes in bacterial cell membranes
– C3b marks them for phagocytes
– C3a and C5a stimulate mast cells to release histamines
InterferonsInterferons - Interfere with viral - Interfere with viral replicationreplication- Block protein synthesis - Block protein synthesis at ribosomesat ribosomes- Activate macrophages- Activate macrophages- Mobilize NK cells- Mobilize NK cells
FeverFever
• When macrophages attack foreign matter, they release chemicals called pyrogens into the blood– Endogenous: interleukins, tumor necrosis factors, macrophage
inflammatory protein, interferons– Exogenous: Lipopolysaccharides of gram-negative bacteria trigger
endogenous factors
• The hypothalamus is stimulated to increase body temperature – fever
• Liver and spleen sequester iron and zinc• High temp. unfavorable for microbes
The Adaptive Immune SystemThe Adaptive Immune System
“Specific” defense mechanisms
• Three characteristics:– recognizes & targets specific foreign
substances– protects the entire body, not a specific
injury or infection site– has a "memory" to store information
from past exposures
Cell RecognitionCell RecognitionProteins, polysaccharides, glycoproteins signal the identity of the cell (host or foreign)
• Major histocompatibility complexes (MHC)– Molecular markers on host cells
• Antigens– Substances that mobilize the immune response
• Molecular markers on foreign cells, abnormal/infected or cancerous host cells
Auto-immune diseases arise when our immune system cannot differentiate “host” from “foreign” cells
Key to Adaptive Immune SystemKey to Adaptive Immune System
• Lymphocytes• Originate from stem cells in bone marrow
• 30% of circulating WBCs
– B cells• mature in Bone marrow
– T cells• mature in Thymus Gland
– Both types are made in the bone marrow– Immune response may be antibody-mediated
(humoral) or cell-mediated
Antibody-mediated ImmunityAntibody-mediated Immunity
• Antibodies: Y-shaped proteins (4 polypeptides) – Made by mature B-
lymphocytes
• Binds to antigens to form antigen-antibody complex
Antibody-mediated ImmunityAntibody-mediated Immunity
• Immunoglobulin classes– IgD: antigen receptor of B cell
– IgM: antigen receptor of B cell (monomer); released by plasma cells during primary response (pentamer)
– IgG: most abundant and diverse; targets bacteria, viruses, toxins; main antibody for both primary and secondary response
– IgA: found in exocrine secretions; prevents pathogens from attaching to epithelial surface
– IgE: bound to mast cells and basophils; mediates inflammation and allergic reaction
Antibody-mediated ImmunityAntibody-mediated Immunity
Antibody-mediated Antibody-mediated ImmunityImmunity
• WBC detects a pathogen or abnormal cell– Attacks pathogen
– Alerts Helper T cells and B cells
• T cells attracted by chemical signals
• B cells alerted by using the pathogen’s own antigens
Antigen
Pathogen
MHC
MHC+Antigen
Signalingmolecules
Helper T cell
B cell
Macrophage
Antibody-mediated Antibody-mediated ImmunityImmunity• Antigens bind to specific
antibodies on B cell surface
• Activation causes B cells to divide rapidly– Plasma cells
• produce antibodies
• 100 million antibodies/hour
– Memory B cells• Remain on “stand by” until
activated by helper T cells
• Surveillance
Cell-mediated Cell-mediated ImmunityImmunity• MHC + antigen
complex waves a warning flag
• Class II MHC’s found on B cells, some T cells, and antigen-presenting cells
• Class I MHC’s found on most cells, except RBCs
Cell-mediated Cell-mediated ImmunityImmunity
AntigenPathogen
MHC
MHC +Antigen
Signalingmolecules
Signalingmolecules
Macrophage
Helper T cell
Cytotoxic T cell
ActivatedCytotoxic T cell
Memory T cell
Perforinmoleculesform poresin pathogencell membrane
• Helper T cells (CD4):– recognize class II MHC– stimulate other immune cells
• Cytotoxic T cells (CD8):– recognize class I MHC– kill infected, cancer, or foreign cells
• Memory T cells:– reactivate on re-exposure
• Suppressor T cells:– suppresses other immune cells
Cell-mediated ImmunityCell-mediated Immunity
• Helper T-cells facilitate both cell-mediated and antibody-mediated immune responses
• Cytotoxic T cells function similar to NK cells, however they only see specific MHC I + antigen complexes
Memory B and T Cells are Like…Memory B and T Cells are Like…
Immune MemoryImmune Memory• Primary immune response
– first exposure to pathogen– recognition, production of B & T cells
• 3 to 6 day lag time• antibodies peak in 10 to 12 days
– B & T memory cells created– basis for "immunity" from the disease
• Secondary immune response– Memory B & T cells immediately identify the
pathogen– faster, longer lasting, more effective than the first– at subsequent infection, new legions of B & T
cells form in a few days– often no symptoms are noticed