Antibodies and Their Functions

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Questions and Answers

What is the primary function of immunoglobulin A (IgA)?

Mediates allergic responses

Provide mucosal immunity (correct)

Activate complement pathways

Neutralize bacterial toxins

Which immunoglobulin is primarily involved in allergic reactions and defense against parasitic infections?

IgE (correct)

IgD

IgG

IgM

Which of the following statements about IgM is true?

It is the most abundant antibody class.

It can cross the placenta.

It indicates intrauterine infection if present in newborns. (correct)

It is mainly found in mucosal secretions.

What role do Fc receptors play in the immune response?

They recognize the Fc region of antibodies. Signup and view all the answers

Which immunoglobulin functions mainly as a B cell receptor?

IgD Signup and view all the answers

What are antibodies primarily produced in response to?

Antigens Signup and view all the answers

Which technique is used to separate proteins in serum for antibody detection?

Serum Protein Electrophoresis Signup and view all the answers

What is the primary function of B cells in antibody production?

To differentiate into plasma cells Signup and view all the answers

What does the constant region of an antibody determine?

The antibody's class and role Signup and view all the answers

Which part of the antibody interacts with the antigen?

Antigen binding fragment (Fab) Signup and view all the answers

What are the hypervariable regions of an antibody responsible for?

Contacting the antigen Signup and view all the answers

Which of the following classes of antibodies is not one of the five main classes?

IgC Signup and view all the answers

How many polypeptide chains make up an antibody?

Four chains Signup and view all the answers

What are the two types of chains found in antibodies?

Heavy Chains and Light Chains Signup and view all the answers

What is the role of membrane-bound antibodies?

Initiate B cell activation Signup and view all the answers

Which immunoglobulin class has subclasses and is involved primarily in secondary immune responses?

IgG Signup and view all the answers

Which IgG subclass has the shortest half-life?

IgG3 Signup and view all the answers

What percentage of total IgG does IgG1 represent?

60-70% Signup and view all the answers

Which type of antibody is the first to be secreted during an immune response?

IgM Signup and view all the answers

Which IgG subclasses are known to bind to Staphylococcal Protein A?

IgG1 and IgG2 Signup and view all the answers

What is a unique feature of IgA compared to other immunoglobulins?

It plays a significant role in mucosal immunity. Signup and view all the answers

Study Notes

Antibodies

Antibodies are glycoproteins found in vertebrates.
They are produced in response to foreign structures called antigens.
Antigens are substances that trigger the production of antibodies.
Antibodies recognize and bind to specific antigens.

Detection of Antibodies in Human Serum

Serum Protein Electrophoresis (SPE) is a lab technique.
It separates serum proteins based on size and charge.
SPE helps diagnose conditions by analyzing protein patterns.
Antibodies are typically found in the gamma globulin fraction of serum.

Production of Antibody

B cells differentiate into plasma cells after stimulation.
Plasma cells secrete antibodies, which are also called immunoglobulins.
Immunoglobulins mediate humoral immunity.
The process involves binding to antigen, chemical signals from helper T cells, becoming plasma cells and releasing antibodies.

Antibody

Gamma globulin proteins react with antigens.
These antigens stimulated their production.
Antibodies make up 20% of plasma protein.
Five classes of antibodies exist: IgG, IgM, IgA, IgD, and IgE.
These classes differ based on heavy chain differences.

Structure of Antibody

Antibodies have a Y-shaped structure.
They consist of four polypeptide chains: two heavy chains and two light chains.
The chains are linked by disulfide bonds for stability.
Variable regions of the Y bind to specific antigens.
The constant region determines the antibody class and its function in the immune response.

Definitions of Fc and Fab Regions

The antigen binding fragment (Fab) recognizes antigens.
The crystallizable fragment (Fc) interacts with immune system components.

Antibody-Binding Site

Within the variable domains, there are three regions with extreme variability.
These highly variable regions are called hypervariable regions.
These regions contact antigens directly.
They form the antigen binding site.
The regions are also referred to as complementarity-determining regions or CDRs.

Variable Regions of Antibodies (Complementarity Determining Regions - CDRs)

CDR's in light and heavy chains of antibodies are highly variable.
These are essential for antigen binding.

Binding of an Antigen by an Antibody

Antibodies bind to antigens using their CDRs.
This binding involves precise interactions between antibody and antigen structures.

Flexibility of Antibody Molecules Via Hinge Region

Antibodies have flexibility via the hinge region.
This flexibility allows for the antibody to bind to antigens in different orientations.

Enzymatic Digestion of Antibodies

Enzymes like papain and pepsin can digest antibodies.
Papain cleaves antibodies into Fab fragments and Fc fragments.
Pepsin cleaves antibodies into F(ab')2 fragments.

Membrane-bound and Secreted Antibodies

Membrane-bound antibodies are critical for B cell activation.
B cells are activated when membrane-bound antibodies bind to specific antigens.
This interaction triggers B cell proliferation and differentiation.

Types of Heavy and Light Chains in Antibodies

Antibodies have various types of heavy chains (gamma, alpha, mu, epsilon, delta).
Antibodies also have kappa and lambda light chains.

Classes and Subclasses of Immunoglobulins

IgG, IgM, IgA, IgD, and IgE are the major classes of immunoglobulins.
Subclasses of immunoglobulins differ based on the heavy chain's structure.

Immunoglobulin G (IgG)

IgG is the most abundant antibody in serum.
It’s important in secondary immune responses.
It provides long-term immunity.
Most subclasses can cross the placenta; important in maternal immunity to the newborn.
IgG participates in complement fixation, precipitation, and neutralization of viruses and toxins.

IgG Subclasses

IgG has four subclasses with differences in half-life, concentration, binding to antigens, transfer across the placenta, Fc binding and complement fixation.

Immunoglobulin M (IgM)

IgM is the first antibody secreted in an immune response.
It's crucial in primary immune responses, serving as a critical early immune response.
IgM is the most important cell surface antibody.
IgM is not transported across the placenta.
High IgM levels in newborns raise concerns for intrauterine infections.

Immunoglobulin A (IgA)

IgA is more abundant than other antibody classes.
It's major in mucosal areas and secretions.
IgA provides crucial mucosal immunity.
IgA exists in dimeric form, with important secretory components enabling transport through mucosal surfaces.

Immunoglobulin E (IgE)

IgE is involved in allergic reactions and defense against parasitic infections.
Low levels of IgE in serum, present on surfaces of mast cells and basophils, enabling these cells to release inflammatory mediators during allergic responses.

Immunoglobulin D (IgD)

IgD functions mainly as a B cell receptor.
IgD has a transmembrane region.

Fc Receptors

Fc receptors are proteins on various cell surfaces that bind to the Fc portion of antibodies.
These receptors' activation triggers various cellular functions and regulates the immune response.

Functions of Antibodies

Antibodies neutralize toxins and viruses.
Antibodies opsonize microbes, facilitating phagocytosis.
Antibody-dependent cell-mediated cytotoxicity (ADCC) eliminates target cells.
Antibodies activate complement to prevent microbes from attaching to mucosal surfaces.
Antibodies mediate complement-dependent cytotoxicity (CDC).

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Description

This quiz covers essential knowledge about antibodies, including their production, detection, and role in the immune response. You'll explore how antibodies interact with antigens and how laboratory techniques like Serum Protein Electrophoresis are used to analyze antibodies in serum. Test your understanding of immunology concepts and mechanisms.