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