adapative immunity pt.2 of notes, part 2

How can plasma cells produce over a billion different types of antibodies?

Through somatic recombination, where gene segments are rearranged to create different antibody genes.

What is somatic recombination?

The process where antibody gene segments are randomly rearranged to create unique antibody receptors.

When does somatic recombination occur?

As B cells become immunocompetent.

What happens after antibody genes are assembled during somatic recombination?

The genes are expressed as receptors on B cells and later produced as antibodies by plasma cells.

What two gene segments contribute to antibody diversity?

• Heavy (H) chain gene segments

• Light (L) chain gene segments

How does random mixing of heavy and light chains increase antibody diversity?

Different combinations of H and L chains create many possible antibody structures.

What are hypervariable regions?

Extremely variable regions within antibody variable regions that create different antigen-binding sites

Why are hypervariable regions important?

They allow antibodies to recognize a huge variety of different antigens.

Can plasma cells produce different antibody classes with the same antigen specificity?

Yes

During the primary immune response, which antibody is produced first?

IgM

During the primary immune response, which antibody follows IgM?

IgG

Which antibody dominates the secondary immune response?

IgG

Why does the secondary immune response contain mostly IgG?

Because memory B cells rapidly produce IgG after re-exposure

What are the two main functions of antibodies?

1. Inactivate antigen-bearing invaders

2. Tag invaders for destruction

What commonly forms when antibodies bind antigens?

Antigen-antibody complexes.

What is complement fixation?

Antibodies bind to cells and activate complement proteins that destroy the target cell.

What type of antigens is complement fixation especially effective against?

Cellular antigens (cells with antigens on their surfaces

What happens when antibodies bind to a cell during complement activation?

Their constant regions change shape, allowing complement proteins to attach and attack the cell.

What does complement activation cause?

• Cell lysis

• Increased inflammation

Increased phagocytosis through opsonization

What is opsonization?

Tagging pathogens so phagocytes can recognize and destroy them more easily.

What is neutralization?

Antibodies bind to specific sites on antigens and prevent them from attaching to cells.

What is the purpose of neutralization?

Prevent toxins, viruses, or pathogens from damaging cells

What is agglutination?

Antibodies cross-link multiple antigen-antibody complexes, causing clumping.

Why is agglutination helpful?

Clumped pathogens are easier for immune cells to identify and remove.

What is precipitation?

Antibodies cross-link soluble antigens into large complexes that settle out of solution.

What happens to precipitated antigen-antibody complexes?

They are captured and consumed by phagocytes.

What creates antibody diversity?

Somatic recombination + random H/L chain combinations + hypervariable regions

What antibody dominates primary response first?

IgM

What antibody dominates secondary response?

IgG

What antibody region activates complement?

Constant region

What antibody region binds antigen?

Variable region

Which mechanism blocks toxins from attaching to cells?

Neutralization

Which mechanism causes clumping?

Agglutination

Which mechanism causes soluble antigens to settle out?

precipitation

What are monoclonal antibodies?

Commercially available, pure antibody preparations that are specific for a single antigenic determinant.

What makes monoclonal antibodies unique?

They all recognize the same antigenic determinant (epitope).

Where do monoclonal antibodies come from?

Descendants of a single antibody-producing cell.

What are hybridomas?

Cells created by fusing tumor cells with B lymphocytes.

Why are hybridomas useful for making monoclonal antibodies?

They combine the useful characteristics of both cell types.

What characteristics do tumor cells provide to hybridomas?

The ability to proliferate indefinitely in culture.

What characteristics do B lymphocytes provide to hybridomas?

The ability to produce a specific antibody.

Why can hybridomas produce large amounts of one antibody type?

They are clones from a single B cell and produce one specific antibody.

What are some diagnostic uses of monoclonal antibodies?

• Pregnancy tests

• Detection of some sexually transmitted diseases

• Some cancers

• Hepatitis

• Rabies

How can monoclonal antibodies treat leukemia and lymphomas?

They can deliver anticancer drugs directly to cancer cells.

Monoclonal antibodies are specific for:

A. Many different antigens
B. A single antigenic determinant
C. All pathogens
D. Only viruses

B

A hybridoma is made by combining:
A. Two B cells
B. Two tumor cells
C. A tumor cell and B lymphocyte
D. A T cell and macrophage

c

The tumor cell component of a hybridoma allows it to:
A. Produce antibodies
B. Destroy pathogens
C. Divide indefinitely
D. Recognize antigens

c

the B lymphocyte component of a hybridoma allows it to:
A. Divide forever
B. Produce a specific antibody
C. Activate complement
D. Become a macrophage

B

What is cell-mediated immunity primarily controlled by?

T cells

What are CD4 cells also called?

T4 cells

What type of T cell are CD4 cells primarily?

Helper T cells (TH cells).

What receptor do CD4 cells display?

CD4 glycoprotein receptors.

What are CD8 cells also called?

T8 Cells

What type of T cell are CD8 cells primarily?

Cytotoxic T cells (TC cells).

What receptor do CD8 cells display?

CD8 glycoprotein receptors.

What are the five major types of T cells?

• Helper T cells (TH)

• Cytotoxic T cells (TC)

• Delayed hypersensitivity T cells (TDH)

• Suppressor T cells (TS)

• Memory T cells

What type of antigens can T cells recognize?

Processed fragments of protein antigens displayed on cell surfaces.

Why are T cells more effective than antibodies against intracellular pathogens?

T cells can attack infected body cells, while antibodies cannot enter cells.

What activates helper T cells?

Specific antigens presented by antigen-presenting cells (APCs)

What is the main function of helper T cells?

Stimulate other immune cells, including cytotoxic T cells and B cells.

What do helper T cells secrete?

Cytokines such as:

• Interleukin-2

• Interleukin-4

• Interleukin-5

What are cytotoxic T cells also called?

• Cytolytic T cells

• CTLs

• Killer T cells

What activates cytotoxic T cells?

Antigen presented by body cells and stimulation from helper T cells.

What do cytotoxic T cells kill?

• Virus-infected cells

• Cancer cells

• Foreign transplanted tissue

What does lymphotoxin do?

Causes DNA fragmentation and promotes inflammation.

What does perforin do?

Creates pores in target cell membranes causing cell lysis.

What is the function of suppressor T cells (TS)?

Stop B and T cell activity after an infection is controlled.

What do suppressor T cells secrete?

Suppressor factors that reduce immune activity.

What is the function of delayed hypersensitivity T cells (TDH)?

Promote macrophage killing and delayed hypersensitivity reactions.

Give an example of a delayed hypersensitivity reaction.

Allergic contact dermatitis from:

• Poison ivy

• Heavy metals

When are memory T cells produced?

During the primary immune response.

How long can memory T cells survive?

years

What is the function of memory T cells?

Provide a rapid response during reinfection with the same antigen.

What is required for T cell cloning?

Double recognition.

What does "double recognition" mean?

T ells must recognize:

1. The antigen

2. The correct MHC protein

Which cells display MHC Class I proteins?

Almost all body cells except red blood cells.

Which T cells recognize MHC Class I?

cD8 cytotoxic T cells.

Where are MHC Class I proteins made?

Endoplasmic reticulum

What type of antigens are presented by MHC Class I?

Endogenous antigens.

What are endogenous antigens?

Foreign proteins made inside body cells, such as from viruses or cancer.

What proteins transport endogenous antigens to MHC Class I?

TAPs (transport proteins).

Which cells display MHC Class II proteins?

• Antigen-presenting cells

• Mature B cells

• Some T cells

Which T cells recognize MHC Class II?

CD4 helper T cells.

What type of antigens are presented by MHC Class II?

Exogenous antigens.

What are exogenous antigens?

Foreign antigens that are engulfed and broken down by cells.

Why does MHC Class II have an invariant chain?

To prevent MHC II from binding peptides inside the ER.

What are the two steps required for T cell activation?

Antigen binding

• Costimulation

What occurs during antigen binding?

T cell receptors (TCRs) bind to an antigen-MHC complex.

What is MHC restriction?

T cells only recognize antigens presented on specific MHC classes.

What is immunologic surveillance?

T cells continuously move around and search cells for recognizable antigens.

What is costimulation?

A second signal required before T cells can proliferate and form clones.

Why is costimulation necessary?

It prevents unnecessary activation of T cells.

Give an example of costimulation.

B7 protein on macrophages binds CD28 receptors on T cells.

Which cytokines can provide costimulation?

• Interleukin-1

• Interleukin-2

Is costimulation required for T-cell cloning?

YES

Compare MHC I vs MHC II.

MHC I

• Found on almost all body cells

• Presents endogenous antigens

• Recognized by CD8 cytotoxic T cells

• Example: virus-infected cells

MHC II

• Found on APCs, mature B cells, some T cells

• Presents exogenous antigens

• Recognized by CD4 helper T cells

• Example: engulfed bacteria

Compare CD4 vs CD8.

CD4

• Helper T cells

• Recognize MHC II

• Activate B cells and other T cells

• Release cytokines

CD8

• Cytotoxic T cells

• Recognize MHC I

• Kill infected/cancer cells

• Release perforin and lymphotoxin