Lecture #123 & 124: Adaptive Immunity 1 & 2

What are the two main arms of the adaptive immune response?

Humoral immunity involving antibodies against extracellular pathogens, and cell-mediated immunity targeting intracellular pathogens.

What does humoral immunity primarily defend against?

Extracellular pathogens using antibodies and is associated with Type I, II, and III hypersensitivity reactions.

What does cell-mediated immunity primarily defend against?

Intracellular pathogens using T cells and is associated with Type IV hypersensitivity reactions.

What is IgE and what is its main function?

A monomer antibody present in low serum levels that binds mast cells and basophils and mediates immediate hypersensitivity reactions.

What cells are primarily involved in IgE-mediated responses?

Mast cells, basophils, and eosinophils, especially in parasitic infections and allergic reactions.

What type of hypersensitivity is mediated by IgE?

Type I hypersensitivity, which includes allergies, asthma, and anaphylaxis.

What is IgM and what are its key characteristics?

A pentamer in circulation, first antibody produced in immune response, effective in agglutination and complement activation, and does not cross the placenta.

What is the function of IgM in immune response?

It is the first antibody produced and is highly effective at activating complement and immobilizing pathogens through agglutination.

Does IgM cross the placenta?

No, IgM does not cross the placenta.

What is IgD and its primary role?

A monomer antibody that functions mainly as a B-cell receptor on naïve B cells.

What is the role of mast cells in hypersensitivity?

They release histamine and other mediators when activated by IgE, leading to allergic symptoms.

What happens during Type I hypersensitivity?

IgE binds to mast cells and basophils, leading to rapid release of inflammatory mediators upon antigen exposure.

What are common examples of Type I hypersensitivity reactions?

Asthma, allergic rhinitis, and anaphylaxis.

What triggers degranulation in Type I hypersensitivity?

Cross-linking of IgE antibodies bound to mast cells by an antigen.

What is anaphylaxis?

A severe, systemic Type I hypersensitivity reaction that can lead to life-threatening airway, breathing, and circulatory compromise.

What distinguishes Type II hypersensitivity?

Antibody-mediated destruction of cells or tissues, often involving IgG or IgM.

What is the mechanism of Type III hypersensitivity?

Immune complex deposition in tissues leading to inflammation and tissue damage.

What distinguishes Type IV hypersensitivity?

It is T-cell mediated and does not involve antibodies, leading to delayed reactions.

Why is Type IV hypersensitivity considered delayed?

Symptoms typically develop 24–72 hours after exposure due to T-cell activation.

What type of pathogens are targeted by cell-mediated immunity?

Intracellular pathogens such as viruses and certain bacteria.

What is the role of eosinophils in immune response?

They are involved in defense against parasitic infections and participate in allergic responses.

What is the importance of antibody isotypes?

Different isotypes have specialized roles in immune defense and hypersensitivity reactions.

What is agglutination in immunology?

The clumping of pathogens by antibodies, primarily IgM, to enhance clearance.

What is complement fixation?

Activation of the complement system by antibodies leading to pathogen destruction.

Why is IgE found in low concentrations in serum?

It is primarily bound to mast cells and basophils rather than circulating freely.

What is the relationship between hypersensitivity reactions and adaptive immunity?

Hypersensitivity reactions are exaggerated or inappropriate adaptive immune responses.

What is the overall purpose of adaptive immunity?

To provide specific, targeted defense against pathogens with memory for faster responses upon re-exposure.