Immunology Class 8: Antibodies and Antigens

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Questions and Answers

What type of immune system are antibodies a part of?

adaptive immune system

What are the three types of antigen recognition molecules?

B Cell (antibody or immunoglobulin), T-Cell (T-cell receptor), All Cells (Major Histocompatibility Complex)

Describe antigens.

Molecules and molecular epitopes that are targets of antibody and specific receptors on T and B cells.

Describe immunoglobulin.

General term for all antibody molecules produced by B cells. Signup and view all the answers

What produces antibodies?

B cells Signup and view all the answers

Describe immunoglobulin structure.

'Y'-shaped molecules with 2 light chains and 2 heavy chains that contain Ig domains. Signup and view all the answers

Describe the Fab component of Ig.

Part of Ab that is adaptable to bind a large number of antigens. Signup and view all the answers

Describe the Fc component of Ig.

Determines biological activities that Ab possesses. Signup and view all the answers

How many isotypes of immunoglobulins exist, and what are they determined by?

Five types, determined by heavy chain. Signup and view all the answers

Describe in descending order the concentration in normal human serum of immunoglobulins.

IgG, IgA, IgM, IgE, IgD. Signup and view all the answers

Which immunoglobulin isotype is never soluble and always membrane-bound?

IgD Signup and view all the answers

What are the two classes of light chains, and describe their association with heavy chains.

Kappa and lambda; LCs on a single Ab are always identical. Signup and view all the answers

Compare and contrast light classes vs heavy classes.

2 LCs, while there are 5 HCs. Signup and view all the answers

Describe variable region.

Each chain contains one at their amino-terminus; makes up the antigen binding site. Signup and view all the answers

Describe the structure of the Fab fragment.

Consist of variable and constant domain from light and heavy chains; fragment of antigen binding. Signup and view all the answers

Describe the structure of the Fc fragment.

Consist of constant domains from heavy chains; fragment able to be crystallized. Signup and view all the answers

Describe disulfide bonds in Ig structure.

Both chains have intramolecular disulfide bonds that help form Ig domains; also involve intermolecular bonds. Signup and view all the answers

Describe hypervariable regions/complementary determining region (CDRs).

Found in each variable region; contains 3 hypervariable regions. Signup and view all the answers

Describe CDR3.

Found in variable regions; greatest variability and most responsible for specific antigen binding. Signup and view all the answers

What determines the immunoglobulin isotype?

Primary amino acid sequence of the heavy chains. Signup and view all the answers

Describe idiotypic differences among Igs.

Determined by the antigenic characteristic of the variable region of both light and heavy chains. Signup and view all the answers

Compare and contrast isotypic vs idiotypic differences.

Isotypic differences are dependent on the heavy chain; idiotypic differences are by the variable region. Signup and view all the answers

What is the major Ig isotype in the serum?

IgG Signup and view all the answers

Describe IgG.

Involved in activation of the classical complement pathway, functions as opsonin, most important in secondary immune responses. Signup and view all the answers

Study Notes

Antibodies and the Immune System

Antibodies are part of the adaptive immune system.
They serve as antigen recognition molecules along with B cells (antibody/immunoglobulin), T cells (T-cell receptor), and all cells (Major Histocompatibility Complex).

Antigens

Antigens are molecules or epitopes that trigger antibody production and specific receptors on T and B cells, typically derived from foreign materials such as proteins and sugars.

Immunoglobulins Overview

Immunoglobulin refers to all antibody molecules produced by B cells, which can exist in soluble or membrane-bound forms.
They recognize specific epitopes on proteins, polysaccharides, lipids, or nucleic acids.
Genetic rearrangement allows for the potential generation of over 10^9 distinct specificities.

Immunoglobulin Structure

Immunoglobulins have a Y-shaped structure consisting of two light chains and two heavy chains containing immunoglobulin (Ig) domains.
Each immunoglobulin molecule has a variable region and constant regions, contributing to their unique functions.

Fab and Fc Components

The Fab (fragment antigen-binding) component has arms that adapt to bind a large number of antigens.
The Fc (fragment crystallizable) component determines the biological activities of the antibody.

Immunoglobulin Isotypes

There are five immunoglobulin isotypes, determined by the heavy chain type.
The typical concentration hierarchy in human serum is: IgG > IgA > IgM > IgE > IgD (acronym: GAMED).
IgD is unique as it is never soluble and is always membrane-bound.

Light and Heavy Chains

There are two classes of light chains: kappa and lambda; they are identical in a single antibody (either 2 kappa or 2 lambda).
Light chains can associate with any heavy chain, contrasting with five distinct heavy chain classes.

Variable Region and Antigen Binding

Each chain's amino-terminus contains a variable region that forms the antigen-binding site, while the remaining domains are constant.
The Fab fragment is essential for antigen binding and consists of both variable and constant domains.

Disulfide Bonds and Stability

Intramolecular disulfide bonds in antibody structure help form Ig domains.
Intermolecular disulfide bonds connect heavy and light chains, playing a crucial role in forming the hinge region.

Hypervariable Regions

Hypervariable regions, or complementary determining regions (CDRs), are critical for specificity in antigen binding, especially CDR3, which shows the greatest variability.

Immunoglobulin Isotype Determinants

The immunoglobulin isotype is determined by the primary amino acid sequence of the heavy chains.

Idiotypic Differences

Differences among immunoglobulins are idiotypic, based on antigenic characteristics of the variable regions.

Comparing Isotypic and Idiotypic Differences

Isotypic differences depend on the heavy chain type (e.g., IgG vs. IgA), while idiotypic differences are based on the variable regions of the chains (e.g., IgG1 vs. IgG2).

Major Immunoglobulin in Serum

IgG is the predominant immunoglobulin isotype present in serum and plays key roles in immune responses.
IgG activates the classical complement pathway, acts as an opsonin, is vital for secondary immune responses, crosses the placenta for neonatal immunity, and is crucial in antibody-dependent cell-mediated cytotoxicity.

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Description

Test your knowledge on antibodies and their role in the immune system with flashcards focused on immunoglobulin classes and antigen recognition molecules. This quiz covers key concepts that are vital for understanding adaptive immunity. Perfect for students of immunology or related fields!