BIOL 261: CH. 27 - ADAPTIVE IMMUNITY: HIGHLY SPECIFIC HOST DEFENSES

Antigen

a molecule capable of interacting with specific components of the immune system and that often functions as an immunogen to elicit an adaptive immune response

B cell receptor (BCR)

a cell surface immunoglobulin that acts as an antigen receptor on a B cell

CD4 coreceptor

a protein found on Th cells that interacts with MHC II on an antigen-presenting cell

CD8 coreceptor

a protein found exclusively on Tc cells that interacts with MHC I on a target cell

Clonal anergy

the inability to produce an immune response to specific antigens due to the neutralization of effector cells

Clonal deletion

for T cell selection in the thymus or B cell selection in the bone marrow, the elimination by apoptosis of useless or self-reactive precursor lymphocytes

Clonal expansion

following its activation, the proliferation and differentiation of a naive T or B lymphocyte into a clone of effector cells

Clone

lymphocytes of identical antigen specificity that have arisen from a single, activated progenitor cell

Epitope

the portion of an antigen that reacts with a specific antibody or T cell receptor

Immune memory (memory)

the ability to rapidly produce large quantities of specific immune cells or antibodies after subsequent exposure to a previously encountered antigen

Immunogen

a molecule capable of eliciting an adaptive immune response

Memory cell

a long-lived B or T lymphocyte responsive to a specific antigen

MHC class I protein

an antigen-presenting molecule found on all nucleated vertebrate cells

MHC class II protein

an antigen-presenting molecule found on macrophages, B cells, and dendritic cells

Primary immune response

the production of antibodies or immune T cells on first exposure to antigen; the antibodies are mostly of the IgM class

Secondary immune response

the enhanced production of antibodies or immune T cells on second and subsequent exposures to antigen; the antibodies are mostly of the IgG class

Specificity

the ability of cells of the adaptive immune response to interact with particular antigens

T cell receptor

an antigen-specific receptor protein on the surface of T cells

T-cytotoxic (Tc) cell

a lymphocyte that interacts with MHC I–peptide complexes through its T cell receptor and produces cytotoxins that kill the interacting target cell

T-helper (Th) cell

a lymphocyte that interacts with MHC II–peptide complexes through its T cell receptor and produces cytokines that act on other cells.

• Th subsets include Th1 cells, which activate macrophages; Th2 cells, which activate B cells; Th17 cells, which activate neutrophils; and Treg cells, which suppress adaptive immunity

Tolerance

the acquired inability to produce an immune response to particular antigens

Vaccination (immunization)

the inoculation of a host with inactive or weakened pathogens or pathogen products to stimulate protective active immunity

What are the 3 characteristics of adaptive immunity?

• Specificity

• Memory

• Tolerance

What is specificity in adaptive immunity?

Response is directed against a specific antigen.

How does memory function in adaptive immunity?

You make memory B & T cells that remember the antigen, leading to a faster secondary response.

What are antibody titers?

The concentration of antibodies in your serum.

Why are antibody titers important?

They help determine immune response strength and whether a person has immunity to a disease.

What is tolerance?

Tolerance is when your body recognizes self-antigens and does not make an immune response (antibody) against your cells (antigens).

What is clonal deletion?

Clonal deletion is the process where cells that would recognize self-antigens are removed or deleted.

What happens when tolerance is lost?

Loss of tolerance results in autoimmune disease.

What is an example of an autoimmune disease caused by loss of tolerance?

Type I diabetes is an example of an autoimmune disease caused by loss of tolerance.

How is type I diabetes managed?

Type I diabetes is managed by giving insulin.

Why do people with type I diabetes need insulin?

People with type I diabetes need insulin because their bodies do not make it.

What happens at the cellular level in type I diabetes?

In type I diabetes, the body makes autoantibodies against the cells in the pancreas that produce insulin.

• The antibody binds to these cells, then complement binds and lyses the cell.

What do B cells differentiate into after antigen exposure?

Plasma cells that make antibodies immediately and memory B cells for future responses.

Which antibody is produced first in the primary immune response?

IgM.

Which antibody is produced in the secondary immune response?

IgG.

Why are haptens not immunogens?

Haptens are too small to cause an immune response on their own.

How can haptens induce an immune response?

By attaching to a larger carrier molecule.

What is an example of a hapten?

Penicillin, which binds to serum proteins to cause an immune response.

What part of an antigen do antibodies interact with?

A distinct portion of the molecule called an antigenic determinant or epitope.

What is an epitope?

It is the antigenic determinant where the antibody (variable region) or TCR binds to the antigen.

What are epitopes composed of?

Proteins (amino acids).

What does MHC stand for and what is its function?

MHC (Major Histocompatibility Complex) consists of antigens/proteins found on cells and plays a role in immune response.

Where is MHC I found?

On all nucleated cells.

Where is MHC II found?

On APCs (antigen-presenting cells), including macrophages, B cells, and dendritic cells.

Why is MHC important in medical procedures?

It is important in organ donations to determine compatibility.

What is active immunity?

When you make the antibodies yourself.

Is active immunity long-term or short-term?

Long-term immunity.

How does natural active immunity occur?

It happens in nature, such as when you get sick and then get well.

What is an example of natural active immunity?

Getting an infection and recovering from it.

What is an example of artificial active immunity?

Receiving a vaccine.

What is passive immunity?

When you are given the antibodies.

Is passive immunity long-term or short-term?

Short-term immunity.

How does natural passive immunity occur?

It happens in nature, such as through breast milk from mother to baby.

What is an example of natural passive immunity?

A baby receiving antibodies through breast milk.

What is an example of artificial passive immunity?

Receiving antivenom, which contains antibodies against snake venom.

How does a B-cell interact with antigens?

A B-cell presents the antigen on its surface with its MHC II.

How do T-helper cells (subset II) respond to antigens?

T-helper cells bind to the antigens with their TCR and secrete cytokines.

What happens when a B-cell is activated by T-helper cells?

The B-cell differentiates into plasma cells that produce antibodies specific to the antigens and memory cells that remember the antigens.

What are the five classes of antibodies?

• IgM

• IgG

• IgA

• IgE

• IgD

What is the function of IgM?

IgM is the first response antibody.

What is the function of IgG?

IgG is involved in the secondary response and provides long-term immunity.

• It also crosses the placenta.

What is the function of IgA?

IgA is a secretory antibody found in mucus and other secretions.

What enzyme breaks down IgA, and what is its significance?

IgAase is the enzyme that breaks down IgA.

• It is a virulence factor for some pathogens, particularly bacteria.

What is the function of IgE?

IgE is associated with allergies and binds to mast cells.

• The constant region binds to the mast cells, leaving the variable region open for more antigens.

What happens when IgE binds to mast cells on subsequent exposures to allergens?

On subsequent exposures, mast cells degranulate, releasing histamine.

What does histamine do?

Histamine is a vasodilator that makes blood vessels larger, releasing fluid into tissues, causing symptoms like runny eyes and nose.

What is the function of IgD?

The specific function of IgD is not well understood.

• It is still considered an antibody.

What is an amnestic response?

An amnestic response is the body's enhanced immune reaction to a pathogen upon subsequent exposure.

• The immune system "remembers" the pathogen, leading to a faster and more robust response compared to the initial exposure.

What do red blood cells (RBCs) lack?

RBCs lack a nucleus and MHC I.

What are the four main blood types?

A, B, AB, and O.

Which blood types have the Rh factor?

A+, B+, AB+, and O+ have the Rh factor.

What are antigens related to blood types?

A, B, and Rh antigens are present on the RBCs.

How is blood typing done?

Blood typing is done using antiserum (antibodies) to determine which antigens are on the RBCs.

What happens if B- blood is transfused into a person with anti-B antibodies?

The anti-B antibodies would bind to the B antigen on the RBCs, causing agglutination (clumping). This could block capillary beds, leading to no gas exchange, acidosis, and potentially death.

What happens when the mom is Rh- and the baby is Rh+?

The mom and baby's blood mix during delivery.

• The mom’s immune system reacts by producing anti-Rh antibodies.

What happens if the next baby is Rh-?

No issues arise because there is no Rh antigen present.

• The mom's body does not produce any antibodies against the baby.

What happens if the next baby is Rh+?

The mom’s anti-Rh antibodies (IgG) cross the placenta.

• The antibodies bind to the baby’s Rh factor on their red blood cells.

• This leads to complement activation, which causes the red blood cells to break down, resulting in erythroblastosis fetalis.

How is erythroblastosis fetalis prevented?

At delivery, the mom is given an Rh- shot (anti-Rh antibody).

• The shot prevents the mom from making anti-Rh antibodies by binding to any fetal Rh+ blood in her system and lysing it.

What do cytotoxic T-cells secrete to attack infected or abnormal cells?

Cytotoxic T-cells secrete granzyme and perforin, which are proteins that help destroy target cells.

How do granzyme and perforin contribute to cell destruction?

Perforin forms pores in the target cell membrane, allowing granzyme to enter and trigger apoptosis (programmed cell death).

What structure is formed on the target cell membrane as a result of cytotoxic T-cell attack?

Membrane attack complexes (MAC) are formed, leading to cell lysis.

What happens to a cell after membrane attack complexes are formed?

The cell undergoes lysis, breaking apart and ultimately dying.

What type of T-cell is associated with CD8?

CD8 is associated with cytotoxic T-cells.

What is the primary function of cytotoxic T-cells?

They lyse infected cells and bind to MHC II.

What type of T-cell is associated with CD4?

CD4 is associated with T-helper cells.

What are the two types of T-helper cells?

Type I and Type II T-helper cells.

What is the function of Type I T-helper cells?

They promote inflammation by secreting cytokines that recruit macrophages and neutrophils.

What is the function of Type II T-helper cells?

They secrete cytokines that direct immune responses.

What causes redness during inflammation?

Increased blood flow due to vasodilation leads to redness.

How does vasodilation contribute to swelling and pain?

Vasodilation increases blood flow, causing fluid buildup (swelling), which can press on nerves and result in pain.

What is the main goal of inflammation?

The goal is to bring white blood cells (WBCs) to the affected area to fight off infection.

Distinguish between immune specificity, memory, and tolerance.

Immune specificity refers to the immune system’s ability to recognize and target specific antigens.

• Immune memory is the ability of the immune system to remember a previously encountered antigen and mount a faster, stronger response upon re-exposure.

• Immune tolerance is the immune system’s ability to recognize and not attack the body’s own cells and harmless substances.

Distinguish between clonal deletion and clonal selection.

Clonal deletion occurs during immune development when self-reactive lymphocytes are eliminated to prevent autoimmune responses.

• Clonal selection happens when a specific antigen activates a matching lymphocyte, leading to its proliferation and differentiation into effector and memory cells.

Where does the antibody bind to an antigen? What part of the antibody binds?

The antibody binds to an antigen at the epitope, a specific region on the antigen’s surface.

• The variable region (Fab) of the antibody binds to the epitope.

Give an example for each: natural and artificial active immunity and natural and artificial passive immunity.

Natural active immunity occurs when a person is exposed to a pathogen and develops immunity, such as recovering from chickenpox.

• Artificial active immunity is when immunity is developed through vaccination, like receiving the MMR vaccine.

• Natural passive immunity happens when antibodies are passed from mother to baby through breast milk.

• Artificial passive immunity is when pre-formed antibodies are administered, such as receiving an antivenom after a snake bite.

Summarize antibody production starting with pathogen interaction with an APC.

A pathogen is engulfed by an antigen-presenting cell (APC), which processes and presents the antigen on MHC class II proteins.

• A helper T cell recognizes the antigen and activates B cells specific to the antigen.

• The B cells proliferate and differentiate into plasma cells, which produce antibodies, and memory B cells, which provide long-term immunity.

What are the different classes of antibody and where are they found? What is unique about each?

IgG is found in blood and extracellular fluid and provides long-term immunity.

• IgA is found in mucosal secretions (saliva, tears, breast milk) and protects mucosal surfaces.

• IgM is the first antibody produced during an infection and is primarily found in the blood.

• IgE is involved in allergic reactions and binds to mast cells and basophils.

• IgD is primarily found on immature B cells and plays a role in B cell activation.