Immune System BasicsImmune System Basics Immunity: The capacity to resist

infectious pathogens. Pathogens: Disease-causing

organisms Self vs. Non-self recognition Major Histocompatibility

Complex (MHC 1) Antigen- a particle or piece of

pathogen an immune system recognizes as foreign.

Immunity: The capacity to resist infectious pathogens.

Pathogens: Disease-causing organisms

Self vs. Non-self recognition Major Histocompatibility

Complex (MHC 1) Antigen- a particle or piece of

pathogen an immune system recognizes as foreign.

MH

C

1

Antigens

1st Defense:Non-specific Immune System

1st Defense:Non-specific Immune System

Reacts immediately after infection- does not need to ID pathogen.1. Barrier Defenses: Skin and Mucous membranes2. Inflammatory Defenses:

Histamine is released at the sign of damage Blood vessels leak fluid and WBC’s

3. Cellular and Molecular Defenses:1. Macrophages: Use pocket transport (phagocytosis) to destroy foreign

particles.2. Natural Killer Cells (NK): Release hydrolytic enzymes onto target cells

to rupture/destroy them. 3. Interferon4. Complement

Reacts immediately after infection- does not need to ID pathogen.1. Barrier Defenses: Skin and Mucous membranes2. Inflammatory Defenses:

Histamine is released at the sign of damage Blood vessels leak fluid and WBC’s

3. Cellular and Molecular Defenses:1. Macrophages: Use pocket transport (phagocytosis) to destroy foreign

particles.2. Natural Killer Cells (NK): Release hydrolytic enzymes onto target cells

to rupture/destroy them. 3. Interferon4. Complement

Final Defense: Specific Immune System

Final Defense: Specific Immune System

Recognizes pathogens and develops a sustained immune response.

Comprised of two parts:1. Cell- Mediated Response2. Humoral ResponseWhite blood cells characters (lymphocytes):

Helper T cells (Th)

Killer T cells (Tc)B cellsMacrophage

Recognizes pathogens and develops a sustained immune response.

Comprised of two parts:1. Cell- Mediated Response2. Humoral ResponseWhite blood cells characters (lymphocytes):

Helper T cells (Th)

Killer T cells (Tc)B cellsMacrophage

Specific Immunity- The Battle Begins!

Specific Immunity- The Battle Begins!

Macrophages search body tissues for pathogens.

Consume pathogens with phagocytosis, kill it with lysosomes, and save the antigens.

Antigens placed into MHC 2 receptors and displayed on macrophage’s membrane.

The macrophage is now considered an antigen-presenting cell (APC).

Macrophages search body tissues for pathogens.

Consume pathogens with phagocytosis, kill it with lysosomes, and save the antigens.

Antigens placed into MHC 2 receptors and displayed on macrophage’s membrane.

The macrophage is now considered an antigen-presenting cell (APC).

Specific Immunity Cont.Specific Immunity Cont. Macrophage chemically signals Helper T to attach to it. Helper T attaches to MHC 2 receptor (with foreign

antigen stuck in it) with a CD4 receptor. Helper T cells have incredible variety of receptors that act

like a “lock and key” in regards to the displayed antigen. If the Helper T’s “key” fits the displayed antigen’s “lock”,

the Helper T is activated. Activation results in Helper T releasing cytokines (ex.

Interleukin)- chemicals that cause lymphocytes to start mitosis.

Macrophage chemically signals Helper T to attach to it. Helper T attaches to MHC 2 receptor (with foreign

antigen stuck in it) with a CD4 receptor. Helper T cells have incredible variety of receptors that act

like a “lock and key” in regards to the displayed antigen. If the Helper T’s “key” fits the displayed antigen’s “lock”,

the Helper T is activated. Activation results in Helper T releasing cytokines (ex.

Interleukin)- chemicals that cause lymphocytes to start mitosis.

Fig. 43-17

Antigen-presentingcell

Peptide antigen

Cell-mediatedimmunity (attack on

infected cells)

Class II MHC moleculeCD4

TCR (T cell receptor)

Helper T cell

Humoralimmunity

(secretion ofantibodies byplasma cells) Cytotoxic T cell

Cytokines

B cell

Bacterium

+

+ +

+

Cell-Mediated ResponseSeek and Destroy

Cell-Mediated ResponseSeek and Destroy

Body cells can be infected by viruses that will hide inside the cell.

As the virus reproduces inside cells, pieces of it fall off and are put into new MHC 1 receptors that the cell puts on its own membrane.

Killer T cells can bind to MHC 1 receptors with their CD8 receptors.

If Killer T binds to MHC 1 receptors with antigen attached, it releases a chemical called perforin.

Perforin ruptures the infected cells membrane and exposes the virus to other immune cells.

Body cells can be infected by viruses that will hide inside the cell.

As the virus reproduces inside cells, pieces of it fall off and are put into new MHC 1 receptors that the cell puts on its own membrane.

Killer T cells can bind to MHC 1 receptors with their CD8 receptors.

If Killer T binds to MHC 1 receptors with antigen attached, it releases a chemical called perforin.

Perforin ruptures the infected cells membrane and exposes the virus to other immune cells.

Fig. 43-11

Antigen

Top view: binding surfaceexposed to antigen receptors

Plasmamembrane ofinfected cell

AntigenClass I MHCmolecule

Fig. 43-18-3

Cytotoxic T cell

Perforin

Granzymes

TCRCD8

Class I MHCmolecule

Targetcell

Peptideantigen

Pore

Released cytotoxic T cell

Dying target cell

Fig. 43-12

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

11

2

22

Humoral SystemBring in the artillery!

Humoral SystemBring in the artillery!

B cells have receptors called antibodies (100,000/cell).

Different B cells have uniquely shaped antibodies that match specific antigens.

If a B cell’s antibody is able to bind with a specific antigen (lock and key effect), the B cell receives a message from Helper T’s to become activated.

Activated B cells divide into Plasma B and Memory B cells.

B cells have receptors called antibodies (100,000/cell).

Different B cells have uniquely shaped antibodies that match specific antigens.

If a B cell’s antibody is able to bind with a specific antigen (lock and key effect), the B cell receives a message from Helper T’s to become activated.

Activated B cells divide into Plasma B and Memory B cells.

Humoral System Cont.Humoral System Cont.

Plasma B cells produce and secrete 10,000 “keyed” antibodies per hour.

Due to their shape, each can bind to several antigens at once.

Antigen/Antibody binding has three effects. Neutralization Macrophage signaling Complement pore formation

Plasma B cells produce and secrete 10,000 “keyed” antibodies per hour.

Due to their shape, each can bind to several antigens at once.

Antigen/Antibody binding has three effects. Neutralization Macrophage signaling Complement pore formation

Fig. 43-21

Viral neutralization

Virus

Opsonization

Bacterium

Macrophage

Activation of complement system and pore formation

Complement proteins

Formation ofmembraneattack complex

Flow of waterand ions

Pore

Foreigncell

Memory B cellsMemory B cells

These cells do not actively produce antibodies Instead, they remain in the bloodstream and

maintain their cell life cycle independently from Th commands.

If the same pathogen/antigen complex presents itself in the future, these cells are already activated and ready to produce antibodies.

There are also Memory versions of Th and Tc cells that serve a similar function.

These cells do not actively produce antibodies Instead, they remain in the bloodstream and

maintain their cell life cycle independently from Th commands.

If the same pathogen/antigen complex presents itself in the future, these cells are already activated and ready to produce antibodies.

There are also Memory versions of Th and Tc cells that serve a similar function.