Immunology: Primary and Secondary Immune Response

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Questions and Answers

What is the primary function of natural killer cells in innate immune defense against intracellular viruses?

To recognize and kill virus-infected cells

What is a key difference between the innate and adaptive immune responses?

The innate immune system does not remember prior encounters with microbes

What type of molecules do phagocytes recognize and respond to?

Microbial cell wall components

What is the term used to describe the microbial molecules that stimulate innate immunity?

Pathogen-associated molecular patterns Signup and view all the answers

What is the function of pattern recognition receptors?

To recognize and respond to microbial cell wall components Signup and view all the answers

Why do the components of innate immunity recognize microbial structures?

Because they are essential for microbial survival and infectivity Signup and view all the answers

What do damage-associated molecular patterns (DAMPs) refer to?

Molecules released from damaged or necrotic host cells Signup and view all the answers

What is the primary function of type I interferons in innate immune defense against viruses?

To block viral replication within host cells Signup and view all the answers

What is the characteristic of naive cells in the immune system?

They are immunologically inexperienced Signup and view all the answers

What is the result of the activation of memory lymphocytes?

Secondary immune response Signup and view all the answers

What is the function of immunologic memory in the immune system?

To combat persistent and recurrent infections Signup and view all the answers

What is the difference between the primary and secondary immune responses to antigen X?

The secondary response is more rapid and larger Signup and view all the answers

What happens to antibody levels over time after each immunization?

They decline Signup and view all the answers

What is the result of lymphocyte activation by antigens?

The proliferation of clonal progeny cells Signup and view all the answers

What is the purpose of clonal expansion in the immune system?

To ensure that adaptive immunity keeps pace with rapidly proliferating microbes Signup and view all the answers

What is a characteristic of immune responses?

They are specialized to defend against different classes of microbes Signup and view all the answers

What is a characteristic of healthy cells that prevents them from being attacked by NK cells?

They do not express ligands for activating receptors. Signup and view all the answers

What is the result of the engagement of inhibitory receptors by healthy cells on NK cells?

The NK cells are not activated. Signup and view all the answers

What is the primary function of the Complement System?

To defend against microbes. Signup and view all the answers

Which pathway of the Complement System is triggered by the presence of antibodies?

The classical pathway. Signup and view all the answers

Which component of the immune system is the alternative pathway a part of?

Innate immunity. Signup and view all the answers

What is the function of mannose-binding lectin (MBL) in the Complement System?

To bind to terminal mannose residues on the surface glycoproteins of microbes. Signup and view all the answers

Which pathway of the Complement System is initiated by a microbial product in the absence of antibody?

The lectin pathway. Signup and view all the answers

What is the result of the activation of the Complement System through any of its three pathways?

The defense against microbes. Signup and view all the answers

Where are the receptors of the innate immune system expressed?

In various cellular compartments where microbes may be located Signup and view all the answers

What is the function of the receptors in the cytosol?

To function as sensors of cytoplasmic microbes Signup and view all the answers

Which protein family do the receptors for PAMPs and DAMPs belong to?

Several protein families Signup and view all the answers

What is the outcome of signals generated by engagement of TLRs?

Stimulation of expression of genes encoding cytokines Signup and view all the answers

Which transcription factors are activated by TLR signals?

Members of the nuclear factor κB family and interferon regulatory factors Signup and view all the answers

What provides physical barriers against infection at the portals of entry of microbes?

Secreted mucus and keratin Signup and view all the answers

What is the function of epithelia in innate immunity?

To provide physical and chemical barriers against infection Signup and view all the answers

What is the characteristic of the receptors of the innate immune system?

They are encoded by inherited genes that are identical in all cells Signup and view all the answers

What happens to naive B cells in peripheral lymphoid tissues during a primary response?

They are activated to proliferate and differentiate into antibody-secreting plasma cells and memory cells. Signup and view all the answers

What is a characteristic of a secondary antibody response?

Production of higher-affinity antibodies with heavy-chain class switching and affinity maturation. Signup and view all the answers

What is the role of B cells in antigen presentation to helper T cells?

B cells recognize native epitopes on antigens and present peptides to helper T cells. Signup and view all the answers

What is the result of antigen receptor-mediated B cell activation?

Initiation of B cell proliferation and IgM secretion, preparing the B cell for interaction with helper T cells. Signup and view all the answers

What is unique about the recognition of antigens by B cells and helper T cells?

B cells recognize native epitopes, while helper T cells recognize peptide fragments of antigens bound to class II MHC molecules. Signup and view all the answers

What do B cells express that may play a role in T cell activation?

Costimulatory molecules (e.g., B7 molecules) Signup and view all the answers

What is the role of helper T cells in a secondary antibody response?

Stimulation of B cells to produce larger amounts of antibodies with heavy-chain class switching and affinity maturation. Signup and view all the answers

What happens to some plasma cells in a primary response?

They migrate to the bone marrow and survive for long periods. Signup and view all the answers

Study Notes

Primary and Secondary Immune Responses

Naive cells are immunologically inexperienced and have not previously responded to antigens.
Secondary responses result from the activation of memory lymphocytes, which are long-lived cells induced during the primary immune response.
Memory lymphocytes remember previous encounters with antigens and respond better upon subsequent encounters.

Antigen-Specific Responses

Antigens X and Y induce the production of different antibodies, reflecting specificity.
The secondary response to antigen X is more rapid and larger than the primary response, illustrating memory.
Antibody levels decline with time after each immunization.

Clonal Expansion and Adaptive Immunity

When lymphocytes are activated by antigens, they undergo proliferation, generating many thousands of clonal progeny cells with the same antigen specificity.
Clonal expansion rapidly increases the number of cells specific for the antigen encountered, ensuring adaptive immunity keeps pace with rapidly proliferating microbes.

Innate Immune Defense

The innate immune system recognizes structures shared by various classes of microbes, not present on normal host cells.
Innate immunity does not remember prior encounters with microbes and resets to baseline after each encounter.
Pattern recognition receptors recognize pathogen-associated molecular patterns (PAMPs) and damaged cells (DAMPs).

Components of Innate Immunity

Phagocytes, natural killer (NK) cells, and cytokines (type I interferons) defend against intracellular viruses.
Different responses are designed to defend against different classes of microbes.

Cellular Receptors for Microbes and Damaged Cells

Receptors for PAMPs and DAMPs are expressed on phagocytes, dendritic cells, and other cell types.
Signals generated by engagement of Toll-like receptors (TLRs) activate transcription factors, stimulating expression of genes involved in antimicrobial functions.

Epithelial Functions in Innate Immunity

Epithelia provide physical and chemical barriers against infection.
Continuous epithelia at portals of entry (skin, gastrointestinal, respiratory, and genitourinary tracts) protect against infection.

The Complement System

The complement system is a collection of circulating and membrane-associated proteins important in defense against microbes.
Complement activation involves the sequential activation of proteolytic enzymes.
Three pathways activate the complement system: alternative, classical, and lectin pathways.

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