Immunology: Antigens and Antibodies

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Questions and Answers

What is the primary function of antibodies in the immune system?

To stimulate the production of vaccines

To destroy pathogens directly

To bind to antigens and help neutralize them (correct)

To produce more antigens

Which type of acquired immunity is characterized by the body producing its own antibodies?

Passive immunity

Natural active immunity (correct)

Artificial passive immunity

Artificial active immunity

What is an example of artificial passive immunity?

Injections of antiserum (correct)

Recovering from a viral infection

Receiving antibodies through breast milk

Immunization with a vaccine

What term describes the specific site where an antibody binds to an antigen?

Epitope Signup and view all the answers

In which of the following situations does natural passive immunity occur?

A mother passing antibodies through breast milk Signup and view all the answers

Which class of molecules do antibodies belong to?

Proteins Signup and view all the answers

What type of immunity involves the administration of a vaccine?

Artificial active immunity Signup and view all the answers

What is the valence of an antibody in the context of its interaction with antigens?

The number of antigens an antibody can bind to simultaneously Signup and view all the answers

Which immunoglobulin is mainly found in mucous, saliva, and tears and forms dimers in secretions?

IgA Signup and view all the answers

What is the molecular weight of IgG?

160,000 Daltons Signup and view all the answers

Which immunoglobulin is the first antibody to arrive in response to initial exposure to an antigen?

IgM Signup and view all the answers

Which type of antibody is involved in hypersensitivity or allergic reactions?

IgE Signup and view all the answers

What percentage of total antibodies in serum is IgD?

0.02% Signup and view all the answers

Which immunoglobulin can cross the fetal-placental membrane?

IgG Signup and view all the answers

What structure does an antibody monomer consist of?

4 polypeptide chains Signup and view all the answers

In an anamnestic response, which antibody appears first during the secondary response?

IgG Signup and view all the answers

What is the primary function of T Helper Cells?

To activate B cells and macrophages. Signup and view all the answers

Which type of T cell is primarily responsible for recognizing and killing target cells?

Cytotoxic T Cells Signup and view all the answers

What do cytokines primarily function as in the immune response?

Chemical messengers that coordinate immune cell activity. Signup and view all the answers

What role do Memory Cells play in the immune system?

They provide a rapid response to previously encountered antigens. Signup and view all the answers

Which type of cells make up approximately 65% of total lymphocytes?

T Cells Signup and view all the answers

What are the 'old' immunoglobulins carried by B Cells?

IgD or IgM Signup and view all the answers

What is the origin of T Cells?

Red bone marrow Signup and view all the answers

Which of the following is NOT a type of T Cell?

Plasma Cells Signup and view all the answers

What is the role of agglutination in the immune response?

Reduces the number of microbes Signup and view all the answers

Which immunological disorder is characterized by a deficiency in both T and B cells?

SCID Signup and view all the answers

In autoimmune diseases, what do antibodies target?

Self-antigens Signup and view all the answers

What is the effect of HIV on T helper (TH) cells?

Decreases the number of TH cells Signup and view all the answers

Which condition is associated with a defective thymus and results in fewer T cells?

DiGeorge Syndrome Signup and view all the answers

What does opsonization enhance in the immune response?

Phagocytosis Signup and view all the answers

Which type of graft involves tissues from different species?

Xenograft Signup and view all the answers

What type of immunoglobulin is primarily involved in allergic reactions?

IgE Signup and view all the answers

Which type of allergic reaction is characterized by symptoms appearing 2-30 minutes after exposure to an allergen?

Type I: Anaphylactic Reaction Signup and view all the answers

What type of antibodies are produced during a Type II Cytotoxic Reaction?

IgG or IgM Signup and view all the answers

Which treatment is commonly used for Type I hypersensitivity reactions?

Anti-histamines or epinephrine Signup and view all the answers

What is a typical time interval for a Type III Immune Complex Reaction to occur?

3-8 hours Signup and view all the answers

Which of the following examples is associated with a Type I Hypersensitivity Reaction?

Hay fever Signup and view all the answers

What occurs during a Type II Cytotoxic Reaction?

Antibodies bind to antigens on target cells, activating complement Signup and view all the answers

What is commonly associated with the secondary consequence of an infection in Type III reactions?

Post-streptococcal Glomerulonephritis Signup and view all the answers

Which of the following is NOT a feature of a Type I hypersensitivity reaction?

Symptoms appear after 5-12 hours Signup and view all the answers

Study Notes

Antigens and Antibodies

Antigen (Ag): substance that triggers antibody formation. Can be a microbe, foreign material, or even "self" material. Usually made of proteins or large polysaccharides.
Antibody (Ab): protein made in response to an antigen. It specifically recognizes and binds to the antigen.
Antigen-Antibody Reaction: The process of an antibody attaching to an antigen at a specific site, forming a complex.
Valence: The number of antigens a single antibody can bind to.

Types of Acquired Immunity

Active Immunity: The body produces its own antibodies.
- Natural Active Immunity: Exposure to a microbe through natural means (like getting a cold).
- Artificial Active Immunity: Deliberate introduction of an antigen through a vaccine. Examples include MMR, DPT or DTaP, and Hib vaccines.
Passive Immunity: The body receives antibodies from another source.
- Natural Passive Immunity: Antibodies transferred from mother to infant through the placenta or breast milk (colostrum).
- Artificial Passive Immunity: Administration of antibodies through injection (e.g., antitoxins, antiserum, Rhogam).

Serum Immunoglobulins

IgA (Secretory Ab): Found in mucous membranes, saliva, tears, colostrum, and blood. Provides the first and third lines of defense. Makes up 13% of total antibodies in serum, but is higher in secretions. Exists as a monomer in blood and a dimer in secretions.
IgD: Primarily an internal marker on B lymphocytes. Makes up only 0.02% of total antibodies. Exists as a monomer.
IgE (Allergic Ab): Involved in allergic reactions and hypersensitivity responses. Makes up only 0.002% of total antibodies. Exists as a monomer.
IgG (Circulatory Ab): The most abundant antibody, making up 80% of total. Protects against microbes and activates complement. Can cross the placental barrier. Exists as a monomer.
IgM (Circulatory Ab): Usually the first antibody produced in response to a new antigen. Short-lived. Does not cross the placental barrier. Makes up 6% of total antibodies. Exists as a pentamer.

Antibody Memory: Anamnestic Response

Titer: A unit of measurement for the level of antibody present in the blood.
Primary Response: Initial exposure to an antigen generally takes time to build immunity. IgM is the first antibody to show up, followed by IgG.
Secondary Response: Upon re-exposure to the same antigen. IgG levels rise much faster and with a greater amount than in the primary response, indicating immune memory.

Antibody Structure

Structure: Antibody molecules are shaped like a Y, formed by four polypeptide chains - two heavy chains and two light chains, joined by disulfide bonds.
Fab Region (Fragment of Antigen Binding): The arms of the Y shape. Contains variable amino acid sequences that are specific to each antigen. This region binds to the antigen.
Fc Region (Fragment of Cell Binding): The stem of the Y shape. Contains constant amino acid sequences. Binds to cells, proteins, or complement.

Development of the Immunological System

T Cells and Cellular Immunity:
- Origin: Stem cells in the red bone marrow.
- Maturation: Thymus gland.
- Function: Play a key role in cell-mediated immunity. They respond to antigens and produce subsets of T cells with specific functions.
- Subsets:
  - T Helper Cells (TH or CD4 Cells): Activate B cells to produce antibodies and activate macrophages. They secrete cytokines.
  - Regulatory T Cells (Suppressor or CD8 Cells): Control and suppress other T cells.
  - Cytotoxic T Cells (TC or CD8 Cells): Recognize and kill target cells, including infected cells ("non-self"), tumor cells, and transplanted foreign tissue. They use programmed cell death (apoptosis).
- Cytokines: Chemical messengers of the immune system. Also known as interleukins, interferons, and tumor necrosis factor (TNF). They regulate immune responses, attract macrophages, protect against viral infections, destroy tumor cells, and increase antibody production.
B Cells and Humoral Immunity:
- Origin: Stem cells in red bone marrow.
- Maturation: Red bone marrow.
- Function: Play a key role in humoral immunity.
- B cells carry "old" immunoglobulins (IgD or M) on their surface. Upon encountering a specific antigen, B cells are activated.
- Activated B cells produce:
  - Memory Cells: Remember the antigen for future encounters.
  - Plasma Cells: Produce the needed specific antibodies.

Results of Antigen & Antibody Binding

Ag-Ab Complex: Antigen binding to antibody creates a complex.
Triggering Mechanisms: Antibody molecules themselves don't directly damage the antigen; instead, they trigger various mechanisms to neutralize the antigen.
Mechanisms:
- Agglutination: Clumping antigens (like bacteria) together, making it easier for them to be phagocytosed.
- Opsonization: Coating an antigen with antibodies, enhancing phagocytosis.
- Neutralization: Blocking viral attachment to cells and neutralizing toxins.
- Complement Activation: Leading to inflammation and lysis of cells.
Complement: A group of serum proteins that work in a cascade to trigger inflammation, opsonization, and lysis of cells.

Immunological Disorders

Congenital Immunodeficiency: Immunodeficiencies present at birth.
- SCID (Severe Combined Immunodeficiency): A rare disorder affecting 1 in 100,000 individuals. Results in a deficiency of both T and B cells, leading to a complete lack of antibodies and increased vulnerability to infections. Treatment often involves gene therapy.
- Bruton's Disease: A rare disorder affecting 1 in 200,000 individuals. Leads to a decrease in B cells and a reduction in antibody production.
- DiGeorge Syndrome: A rare disorder affecting the development of the thymus gland, resulting in fewer T cells and vulnerability to infections.
Autoimmune Diseases: The immune system attacks the body's own tissues.
- Rheumatoid Arthritis (RA): Focuses on joints. Antibodies target gammaglobulins, leading to inflammation.
- Systemic Lupus Erythematosus (SLE): Characterized by antibodies against DNA, leading to inflammation across various tissues.
AIDS (Acquired Immunodeficiency Syndrome): Caused by HIV, which attacks CD4 receptors on T helper cells, leading to a decline in the number of TH cells. This weakens the immune system, making individuals more susceptible to infections and cancers.

Tissue Transplantation

Autograft: Transplantation of tissue from one part of the body to another in the same individual.
Isograft: Transplantation of tissue between genetically identical individuals (e.g., identical twins).
Xenograft or Heterograft: Transplant of tissue between individuals of different species.
Homograft or Allograft: Transplant of tissue between individuals of the same species, but different genetically.
GRAFT REJECTION: The immune system recognizes the transplanted tissue (allograft or xenograft) as foreign and mounts an attack.
Histocompatibility: The degree of genetic similarity between donor and recipient.
HLA (Human Leukocyte Antigen) Complex: A group of genes that control histocompatibility. The more similar the HLA genes between donor and recipient, the lower the chance of rejection.

Allergic Disorders: Hypersensitivity

Hypersensitivity Reactions: An exaggerated immune response to a harmless substance known as an allergen.
Types:
- Immediate (Antibody-mediated)
  - Type I: Anaphylactic Reactions: Immediate, rapid-onset allergic reaction. Often triggered by allergens such as insect stings, certain foods, and drugs.
    - Sensitizing Dose (First Exposure): Leads to the production of IgE antibodies. The Fab region of IgE binds to the allergen, while the Fc region attaches to mast cells or basophils.
    - Shocking Dose (Second Exposure): Causes rapid release of histamine, leading to symptoms like hives, itching, and anaphylactic shock.
    - Treatment: Antihistamines, epinephrine (to constrict blood vessels and increase blood pressure).
    - Lab Tests: Skin tests, eosinophilia, IgE levels (RAST).
  - Type II: Cytotoxic Reactions: Involve the destruction of cells. Often seen in transfusion reactions or Hemolytic Disease of the Newborn (HDN).
    - IgG or IgM antibodies bind to the antigen on cell surfaces, triggering the complement system and lysis (destruction) of those cells.
  - Type III: Immune Complex Reactions: Occur when an antigen combines with an antibody (IgG or IgM) to form an immune complex.
  - These complexes stick to blood vessel walls, triggering inflammation.
- Delayed (Cell-mediated)
  - Type IV: Delayed Type Reactions: Occur 24-72 hours after exposure. Involve T cell responses rather than antibodies. Examples include contact dermatitis (like poison ivy).
  - Triggered by exposure to common allergens and involves the release of cytokines and recruitment of inflammatory cells.

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Description

Test your knowledge on antigens, antibodies, and the types of acquired immunity. This quiz covers fundamental concepts like the antigen-antibody reaction and the distinctions between active and passive immunity. Dive into the world of immunology and evaluate your understanding!