Unit 3 Module C

What line of defense is adaptive (acquired) immunity?

The third line of defense

What two features distinguish adaptive immunity from innate immunity?

Specificity and memory.

What does specificity mean in adaptive immunity?

The ability to recognize and respond to a single, precise antigen.

What does immunological memory mean?

Faster and stronger immune responses upon subsequent exposures to the same antigen.

What are four major functions of cell surface markers in immunity?

Attach to foreign antigens; recognize self antigens; receive chemical messages; transmit chemical messages between immune cells.

What is MHC?

Major Histocompatibility Complex; cell surface markers involved in immune recognition.

Where is Class I MHC found?

On all nucleated cells (not red blood cells).

What is the function of Class I MHC?

Displays “self” markers for immune recognition.

Where is Class II MHC found?

Only on antigen‑presenting cells (APCs).

What is the function of Class II MHC?

Presents processed antigens to T helper (CD4⁺) cells.

What two types of lymphocytes carry out adaptive immunity?

B cells and T cells.

Where do B cells mature?

Bone marrow.

Where do T cells mature?

Thymus.

What type of antigens do B cell receptors bind?

Free (unprocessed) antigens.

What type of antigens do T cell receptors bind?

Processed antigens presented with MHC molecules.

What are the specific receptors on B cells called?

Immunoglobulins (antibodies).

What is the variable region of an antibody?

The antigen‑binding site.

Why is antibody variability important?

It allows recognition of a wide variety of antigens.

What are two major T cell receptor classes?

CD4 and CD8.

What do B cells differentiate into after activation?

Plasma cells and memory B cells.

What type of immunity do B cells mediate?

Antibody‑mediated (humoral) immunity.

Can B cells act as antigen‑presenting cells?

Yes.

What type of immunity do T cells mediate?

Cell‑mediated immunity.

Do T cells produce antibodies?

No.

What do T cells act directly against?

Infected, abnormal, or foreign cells.

What is an antigen?

Any substance capable of triggering a specific immune response.

How does molecular weight affect antigen strength?

<1,000 MW: rarely antigenic; 1,000–10,000 MW: weak antigens; >100,000 MW: most immunogenic.

What is an epitope?

The specific antigen fragment recognized by immune cells.

What is a hapten?

A small molecule that is only antigenic when attached to a larger carrier molecule.

What three cells can function as antigen‑presenting cells?

Macrophages, dendritic cells, and B cells.

Which cell type must recognize processed antigens?

T helper (CD4⁺) cells.

Where do APCs display processed antigens?

On Class II MHC molecules.

What receptor on T helper cells recognizes the antigen?

T cell receptor (TCR).

What role does CD4 play during antigen recognition?

Stabilizes binding to MHC II.

What cytokine activates T helper cells?

Interleukin‑1 (IL‑1).

What cytokine do activated T helper cells release to stimulate B and T cells?

Interleukin‑2 (IL‑2).

What happens to B cells after activation by T helper cells?

Clonal expansion.

What is the function of plasma cells?

Short‑lived cells that secrete large amounts of antibodies.

What is the function of memory B cells?

Provide long‑term immunity and rapid response upon re‑exposure.

What is neutralization?

Antibodies block viruses or toxins from attaching to host cells.

What is opsonization?

Antibodies coat microbes to enhance phagocytosis.

What is agglutination?

Antibody‑mediated clumping of antigens.

What is precipitation?

Formation of insoluble antigen‑antibody complexes.

What is complement fixation?

Activation of complement leading to cell lysis, inflammation, and enhanced phagocytosis.

Which antibody is most abundant in serum?

IgG.

Which antibody can cross the placenta?

IgG.

Which antibody is found in secretions and breast milk?

IgA.

Which antibody is associated with allergies?

IgE.

Which antibody is a pentamer and produced first?

IgM.

Which antibodies can fix complement?

IgG and IgM.

Which antibody functions as a B‑cell receptor?

IgD.

Which antibody is produced first during the primary response?

IgM.

Which antibody follows in greater concentration during the primary response?

IgG.

Why is there no lag time in the secondary (anamnestic) response?

Memory B cells are already present.

Which antibody predominates during the secondary immune response?

IgG

What are the two main types of T cells?

T helper (CD4⁺) and T cytotoxic (CD8⁺).

Which T cells are severely reduced in AIDS patients?

T helper (CD4⁺) cells.

What is the primary function of T helper cells?

Coordinate immune responses by releasing cytokines.

What is the primary function of T cytotoxic cells?

Destroy virus‑infected, cancerous, or foreign cells.

What substances do cytotoxic T cells release to kill target cells?

Perforin and granzymes.

How do superantigens activate the immune system?

They bind MHC II and T‑cell receptors simultaneously, causing nonspecific T‑cell activation.

Why are superantigens dangerous?

They cause excessive cytokine release leading to toxic shock and organ failure.

What is active immunity?

Immunity produced by an individual’s own immune response.

What is passive immunity?

Immunity gained through pre‑formed antibodies.

What is natural immunity?

Immunity acquired without medical intervention.

What is artificial immunity?

Immunity acquired through medical procedures.

Example of natural active immunity

Recovery from an infection.

Example of natural passive immunity

Maternal antibodies passed through breast milk.

Example of artificial active immunity

Vaccination

Example of artificial passive immunity

Injection of immune serum or antibodies.

What does vaccination expose the body to?

Immunogenic but non‑pathogenic material.

What are the requirements for an effective vaccine?

Strong immune response, long‑term memory, safety, stability, and no disease caused.

What are the drawbacks of killed or inactivated vaccines?

Weaker immune response and need for booster shots.

What is the advantage of attenuated vaccines?

Long‑lasting immunity with fewer doses.

What is the risk of attenuated vaccines?

Reversion to a virulent strain.

What is herd immunity?

Population‑level immunity that reduces disease spread and protects nonimmune individuals.