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BellworkBellworkDiscuss with your group what you
think is happening in the following processes. ◦Why does your body undergo an
allergic reaction?◦Why do some people’s bodies attack
themselves (autoimmune diseases)?◦How does AIDS escape the human
immune systems?◦Why do we have an inflammatory
response when we are injured?
Innate immunityInnate immunityPresent before any exposure to
pathogens and is effective from the time of birth
Involves nonspecific responses to pathogens
Innate immunity consists of external barriers plus internal cellular and chemical defenses
Acquired immunityAcquired immunity,,AKA adaptive immunity, develops
after exposure to agents such as microbes, toxins, or other foreign substances
It involves a very specific response to pathogens
Major parts of Innate Major parts of Innate ImmunityImmunityBarrier defensesPhagocytosisAntimicrobial peptidesInflammatory responseNatural killer cells
Innate Immunity - Innate Immunity - PhagocytosisPhagocytosis
Groups of pathogens are recognized by TLR, Toll-like receptors
Once recognized, cells engulf the pathogen
Innate Immunity - Innate Immunity - PhagocytosisPhagocytosisThere are different
types of phagocytic cells:◦ Neutrophils engulf and
destroy microbes◦ Macrophages (big
eaters) are part of the lymphatic system and are found throughout the body
◦ Eosinophils discharge destructive enzymes to kill multicellular parasites
◦ Dendritic cells stimulate development of acquired immunity
Innate Immunity – Innate Immunity – antimicrobial peptides (AKA antimicrobial peptides (AKA proteins)proteins)
Interferons – induce nearby viral infected cells to secrete substances that inhibit viral reproduction
Complement system- Proteins in the blood plasma that fight infection. Can react to form a complex that leads to lysing of invading cells
Innate Immunity – Innate Immunity – Inflammatory responseInflammatory responseChanges brought about by chemical
signal◦At the site, mast cells in the connective
tissue release histamine◦Histamine triggers nearby blood vessels
to dilate and become more permeable◦This helps deliver antimicrobial proteins,
neutrophils and macrophages◦Pus, a fluid rich in white blood cells,
dead microbes, and cell debris, accumulates at the site of inflammation
Fig. 43-8-3
Pathogen Splinter
Macrophage
Mast cell
Chemicalsignals
Capillary
Phagocytic cellRed blood cells
Fluid
Phagocytosis
Check for UnderstandingCheck for UnderstandingOn a sheet of paper, write an
essay to describe the inflammatory response
Innate Immunity - Natural Innate Immunity - Natural Killer CellsKiller CellsHelp recognize and eliminate
certain diseased cells
DefineDefineAntigenAntibodylymphocytes
Acquired ImmunityAcquired ImmunityWhite blood cells recognize and
respond to antigens (foreign molecules) and then create immunological memory
Lymphocytes that mature in the thymus are called T cells, and those that mature in bone marrow are called B cells
Acquired ImmunityAcquired ImmunityB cells and T cells have receptor
proteins that can bind to foreign molecules
Each individual lymphocyte is specialized to recognize a specific type of molecule
Acquired Immunity – With all Acquired Immunity – With all the variation in receptors, the variation in receptors, why does it not attack itself?why does it not attack itself?As lymphocytes mature in bone
marrow or the thymus, they are tested for self-reactivity
Lymphocytes with receptors specific for the body’s own molecules are destroyed by apoptosis, or rendered nonfunctional
Acquired ImmunityAcquired ImmunityB cells can make receptors that
detach from the cell membrane (antibody)
Epitope – a foreign molecule that a specific antibody or lymphocyte binds to
But Before we talk about But Before we talk about that… lets see how it all that… lets see how it all beginsbeginsA cell engulfs the pathogen
(either a regular cell, dendritic cells, macrophages, and B cells)
Molecules within the cells attach to the antigen and present it to T cells
Fig. 43-12
1
Infected cell
Antigenfragment
Class I MHCmolecule
T cellreceptor
(a)
Antigenassociateswith MHCmolecule
T cellrecognizescombination
Cytotoxic T cell (b) Helper T cell
T cellreceptor
Class II MHCmolecule
Antigenfragment
Antigen-presentingcell
Microbe
1
1
2
22
Class I MHC is found in all body cells and can only present it to cytotoxic T cells
Class II MHC is found in specialized phagocytic cells, such as dendritic cells, macrophages and B cells. These present the antigen to either cytotoxic T cells or Helper T cells
Once they recognize the Once they recognize the antigen they call for help!antigen they call for help!Acquired immunity has two branches:
the humoral immune response and the cell-mediated immune response
Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies
Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells
*Helper T cells can stimulate either response
A focus on cell mediated A focus on cell mediated responseresponseActivated helper T cells secrete
cytokines that stimulate other lymphocytes◦Includes cytotoxic T cells which kill
the infected cells
A focus on cell mediated A focus on cell mediated responseresponseThe binding of a mature
lymphocyte to an antigen induces the lymphocyte to divide rapidly
This proliferation of lymphocytes is called clonal selection
Two types of clones are produced: short-lived activated effector cells and long-lived memory cells
Lets see it again!
Now, the humoral Now, the humoral responseresponse
A focus on the humoral A focus on the humoral responseresponseThe helper T cell sends signals to
recruit B cells The B cells proliferate into
memory cells and plasma cells
A focus on the humoral A focus on the humoral responseresponseThe B cells send out antibodies
The Role of Antibodies in ImmunityNeutralization occurs when a pathogen
can no longer infect a host because it is bound to an antibody
Opsonization occurs when antibodies bound to antigens increase phagocytosis
Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis
There are different types of There are different types of antibodiesantibodies
Why is our body better at Why is our body better at fighting a pathogen off the fighting a pathogen off the second time?second time?The first exposure to a specific
antigen represents the primary immune response
During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms
In the secondary immune response, memory cells facilitate a faster, more efficient response
SummarizeSummarizeCompare and contrast B and T
cells
So now… what are So now… what are vaccinations and how does vaccinations and how does this help our immune this help our immune system?system?We introduce the epitope to our
bodies so our body makes memmory cells, then when our immune system is faced with the actual pathogen, it can quickly destroy it
What are allergies?What are allergies?Allergies are exaggerated
(hypersensitive) responses to antigens called allergens
In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells
AllergiesAllergies
Autoimmune disordersAutoimmune disordersWhat do you think has gone
wrong?The mechanisms for detecting
receptors that attack its own cells are not working properly
BellworkDiscuss with your group why your
immune system does not have a secondary response to AIDS like most other viruses. How does it escape the immune system?
AIDSHuman immunodeficiency virus
(HIV) infects helper T cellsThe loss of helper T cells impairs
both the humoral and cell-mediated immune responses and leads to AIDS
HIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA