Immunology - lecture 6

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Questions and Answers

What is the function of the hinge region in an antibody molecule?

To differentiate between isotypes

To provide structural stability

To bind to specific antigens

To allow flexibility in binding to multiple antigens (correct)

Which fragment of the antibody does not interact with the antigen?

Fragment crystallizable (Fc) (correct)

Fragment antigen binding (Fab)

Variable region

Hinge region

How many equal-sized globular portions does a fully assembled antibody molecule comprise?

Four

Two

Three (correct)

Five

What component differentiates between antibody isotypes?

The heavy chain Signup and view all the answers

Which part of the antibody is responsible for antigen-binding activity?

Fragment antigen binding (Fab) Signup and view all the answers

What is the structural form of IgM molecules found in plasma?

Pentamers Signup and view all the answers

In what form are IgA molecules primarily found in mucous secretions?

Dimers Signup and view all the answers

What characteristic of IgM antibodies helps compensate for the low affinity of individual binding sites?

Multisite binding Signup and view all the answers

What part of the antibody molecule forms the antigen-binding site?

Variable regions Signup and view all the answers

What is the result of somatic hypermutation and affinity maturation in antibody development?

Higher individual binding site affinity Signup and view all the answers

What are the hypervariable regions of an antibody also known as?

Complementarity-determining regions Signup and view all the answers

Which part of the antibody structure is primarily responsible for binding to antigens?

N-terminal domains Signup and view all the answers

What is the process called that allows the immune system to generate antibodies with different specificities?

Combinatorial diversity Signup and view all the answers

How many hypervariable regions are present in the variable domains of antibodies?

3 Signup and view all the answers

What characterizes adaptive immunity compared to innate immunity?

It is based on specificity and diversity. Signup and view all the answers

What is the main function of the constant regions of an antibody?

Biological function other than binding Signup and view all the answers

Which chains typically compose the T-cell receptor (TCR)?

Alpha and beta chains Signup and view all the answers

Where do T cells mature in the immune system?

In the thymus. Signup and view all the answers

What regions provide the structural framework in the variable domain of antibodies?

Framework regions Signup and view all the answers

What is the primary function of plasma cells in the adaptive immune response?

To produce antibodies. Signup and view all the answers

What is the typical structure of a TCR?

Two protein chains Signup and view all the answers

Which type of immune cell is responsible for cytotoxic activity?

Cytotoxic T cells. Signup and view all the answers

What defines an antigen's recognition by lymphocytes?

It is any molecule recognized by BCRs/TCRs. Signup and view all the answers

What is a major characteristic that distinguishes innate immunity from adaptive immunity?

Innate immunity is limited in recognizing diverse pathogens. Signup and view all the answers

Which cells assist other immune cells in their functions?

Helper T cells. Signup and view all the answers

What statement is accurate regarding the recognition of pathogens by innate immune cells?

They recognize pathogen-associated molecular patterns (PAMPs). Signup and view all the answers

What is the role of CD8 in the immune response?

Binds to MHC-I molecules Signup and view all the answers

What is required for TCR to be expressed on the surface of T cells?

CD3 complex Signup and view all the answers

Which protein chains constitute the αβ T-cell receptor?

TCR α and TCR β Signup and view all the answers

Which statement about T-cell receptors (TCRs) is FALSE?

They can be secreted into the extracellular space. Signup and view all the answers

What is the significance of MHC restriction in T-cell responses?

It mandates T cells to interact with both peptide antigens and MHC molecules. Signup and view all the answers

What subunits are part of the CD3 complex?

Six subunits Signup and view all the answers

Which class of MHC molecules interacts with CD4 molecules?

MHC Class II Signup and view all the answers

Which of the following is NOT a characteristic of αβ T-cell receptors?

They consist only of TCR α chains. Signup and view all the answers

Study Notes

Adaptive vs. Innate Immunity

Adaptive immunity utilizes specific receptors to recognize diverse molecules, while innate immunity relies on general recognition mechanisms.
Adaptive immunity provides long-lasting protection against specific pathogens, while innate immunity provides immediate, but less specific, defense.

Cells of the Adaptive Immune System

Lymphocytes are the primary cells of the adaptive immune system.
B cells mature in bone marrow and are responsible for antibody production (humoral immunity).
T cells mature in the thymus and contribute to cell-mediated immunity.
- Helper T cells (CD4+) assist cytotoxic T cells and B cells.
- Cytotoxic T cells (CD8+) directly kill virus-infected and damaged cells.

Antigen and Epitope

An antigen is any molecule, or part of a molecule, recognized by the body as foreign.
An epitope is the specific region of an antigen that binds to an antibody or T-cell receptor.

Antibody Structure

Antibodies are composed of four polypeptide chains: two identical heavy (H) chains and two identical light (L) chains.
The variable (V) regions at the N-terminus of each chain determine antigen specificity.
The constant (C) regions at the C-terminus of each chain determine the antibody's biological function and isotype.
The hinge region provides flexibility for binding to multiple antigens.
Fragment antigen-binding (Fab) region binds to antigens.
Fragment crystallizable (Fc) region interacts with other immune cells and molecules.

Antibody Isotypes

Antibody isotypes are defined by differences in the constant region of the heavy chain.
Five major isotypes include: IgM, IgG, IgD, IgA, and IgE.
IgM is the first antibody produced during an immune response.
IgG is the most abundant antibody in serum and provides long-lasting immunity.
IgA is found in mucosal secretions and protects against pathogens entering the body.
IgD functions as an antigen receptor on B cells.
IgE is involved in allergic reactions.

Complementarity-determining Regions (CDRs)

Hypervariable regions within the variable domains of antibodies form CDRs.
CDRs make up the antigen-binding site and are responsible for antibody specificity.

Combinatorial Diversity

Antibodies with differing specificities are generated through combinatorial diversity.
This process involves assembling different V, D, and J gene segments to create unique variable regions.

T-Cell Receptor (TCR) Structure

TCRs are transmembrane proteins that recognize antigen presented by MHC molecules.
Most TCRs are composed of two chains: α and β.
Each chain has a constant (C) region and a variable (V) region.

TCR Complex

The TCR complex consists of the TCR, the CD3 complex, and co-receptors (CD4 or CD8).
The CD3 complex is essential for TCR signaling and brings the TCR to the cell surface.
CD4 co-receptor binds to MHC class II molecules.
CD8 co-receptor binds to MHC class I molecules.

MHC Restriction

T cells recognize antigen in the context of MHC molecules.
MHC class I presents intracellular antigens to CD8+ T cells.
MHC class II presents extracellular antigens to CD4+ T cells.

Summary

Adaptive immunity is characterized by specific recognition of antigens through B-cell receptors (BCRs) and T-cell receptors (TCRs).
BCRs are antibodies that recognize diverse antigens and trigger antibody production.
TCRs recognize peptide antigens presented by MHC molecules, leading to activation of T cells for specific immune responses.
The diversity of BCRs and TCRs is generated through complex mechanisms of gene recombination and somatic hypermutation.

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Description

This quiz explores the key concepts of adaptive versus innate immunity, focusing on the cells involved in the adaptive immune system, such as B and T cells. It also covers important terminology like antigens and epitopes, along with the structure of antibodies. Test your knowledge on these vital components of the immune response.