Lecture 9 — Adaptive Immunity
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1
What is adaptive immunity?
A specific immune response that develops after exposure to an antigen.
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Why is adaptive immunity needed in addition to innate immunity?
Some pathogens can evade innate defenses, so the body needs a more targeted response.
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What are the four key characteristics of adaptive immunity?
Specificity, inducibility, memory, and tolerance to self.
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What does specificity mean in adaptive immunity?
The immune system recognizes particular antigens or epitopes.
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What does inducible mean?
The response must be activated by exposure to a specific antigen.
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What is immunological memory?
The ability to respond more quickly and strongly after encountering an antigen again.
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Why must adaptive immunity be tolerant to self?
To prevent the immune system from attacking the body's own cells and tissues.
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What can happen when tolerance to self fails?
An autoimmune disorder can develop.
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What are the two major branches of adaptive immunity?
Humoral immunity and cell-mediated immunity.
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What is humoral immunity?
Antibody-mediated immunity that uses antibodies circulating in body fluids.
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Which cells produce antibodies?
B lymphocytes that differentiate into plasma cells.
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What is cell-mediated immunity?
Adaptive immunity that uses T cells to recognize and act against infected or abnormal cells.
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Which cells are central to cell-mediated immunity?
T lymphocytes, especially cytotoxic T cells.
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What types of pathogens are especially targeted by humoral immunity?
Extracellular pathogens and toxins.
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What types of pathogens are especially targeted by cell-mediated immunity?
Intracellular pathogens.
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How do cytotoxic T cells help defend the body?
They recognize and kill infected or abnormal host cells.
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How can cell-mediated immunity help protect against cancer?
It can recognize and destroy cells displaying abnormal or tumor-associated antigens.
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Why can cell-mediated immunity cause transplant rejection?
It may recognize donor tissue as foreign and attack it.
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What is an antigen?
A substance recognized by the immune system.
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What is an epitope?
The specific part of an antigen that an immune receptor recognizes.
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Can one antigen contain multiple epitopes?
Yes. Different parts of one antigen can be recognized separately.
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What is a B-cell receptor?
An antigen-binding receptor attached to the surface of a B cell.
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How is a B-cell receptor related to an antibody?
It is structurally similar to an antibody but remains attached to the B-cell surface.
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What is a T-cell receptor?
A receptor on a T cell that recognizes a specific antigen fragment presented by an MHC protein.
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What does MHC stand for?
Major histocompatibility complex.
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What is the function of MHC proteins?
They display antigen fragments on cell surfaces for T-cell recognition.
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Where is MHC class I found?
On nearly all nucleated cells in the body.
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Which cells are notable exceptions to MHC class I expression in the lecture?
Red blood cells and sperm cells.
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What type of antigen does MHC class I present?
Endogenous antigens from inside the cell.
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Which T cells interact with MHC class I?
CD8-positive cytotoxic T cells.
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What does CD8 bind to?
MHC class I.
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What type of antigen does MHC class II present?
Exogenous antigens taken up from outside the cell.
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Which cells express MHC class II?
Professional antigen-presenting cells, including dendritic cells, macrophages, and B cells.
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Which T cells interact with MHC class II?
CD4-positive helper T cells.
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What does CD4 bind to?
MHC class II.
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What is an antigen-presenting cell (APC)?
A cell that processes antigens and displays antigen fragments on MHC proteins.
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What is cross-presentation?
The ability of dendritic cells to present exogenous antigens on both MHC class II and MHC class I.
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Why is cross-presentation important?
It allows dendritic cells to help activate cytotoxic T-cell responses to antigens taken up from outside the cell.
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Where do dendritic cells go to activate T cells?
Lymph nodes.
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What is clonal expansion?
The multiplication of an activated lymphocyte to produce many cells with the same antigen specificity.
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What happens when a helper T cell recognizes its matching antigen on an APC?
It becomes activated and can help coordinate an adaptive immune response.
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How do helper T cells help activate B cells?
They recognize matching antigen presented by B cells and provide activating signals.
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What happens to an activated B cell?
It undergoes clonal expansion and differentiates into plasma cells and memory B cells.
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What is a plasma cell?
A differentiated B cell that secretes antibodies.
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What is a memory B cell?
A long-lived B cell that helps produce a faster response after future exposure to the same antigen.
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What are T-independent antigens?
Antigens that can activate B cells without helper T-cell assistance.
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What kinds of structures can act as T-independent antigens?
Some long, repeating polymers such as bacterial capsules and flagella.
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