Antigens and Epitopes in Immunology

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Questions and Answers

What are epitopes?

Proteins that act as antigens

Small parts of an antigenic molecule that stimulate the specific immune system (correct)

Substances that become immunogenic when bound to a carrier molecule

Foreign substances that stimulate the immune system

Which of the following factors does NOT influence antigenicity?

Foreignness

Molecular size

Chemical nature

Climate (correct)

What does an adjuvant do?

Prolongs the stimulation of the immune response (correct)

Acts as a self-antigen

Stimulates the production of epitopes

Increases the molecular size of antigens

Which type of molecule is typically NOT antigenic?

Lipids Signup and view all the answers

What is the consequence of excessive antigen dosage?

Immune suppression Signup and view all the answers

Which of the following is true about haptens?

They require a carrier molecule to become immunogenic Signup and view all the answers

How many different epitopes are present on human albumin, at minimum?

At least six Signup and view all the answers

Which routes of administration of antigens are known to induce a slower but stronger immune response?

Intramuscular routes Signup and view all the answers

Which cells interact with MHC class I molecules?

CD8+ Tc cells Signup and view all the answers

What types of HLA are associated with class II MHC?

HLA-DQ,P,R Signup and view all the answers

On which type of cells are MHC class I molecules found?

All nucleated cells Signup and view all the answers

Which of the following functions is associated with class II MHC molecules?

Stimulates Th cells Signup and view all the answers

Why is the MHC significant in organ transplantation?

Due to graft rejection Signup and view all the answers

Which HLA antigen is associated with ankylosing spondylitis?

HLA-B27 Signup and view all the answers

What can result from administering very high or very low doses of certain antigens?

Immunologic tolerance Signup and view all the answers

Why are parental routes preferred over oral routes for antigen administration?

They induce stronger immune responses Signup and view all the answers

What is the role of an adjuvant in vaccination?

Increase the immune response Signup and view all the answers

What is required to stimulate a strong immune response when administering antigens?

Repeated booster doses Signup and view all the answers

What transforms a hapten into an antigenic determinant?

Conjugation to a carrier protein Signup and view all the answers

Which of the following is not typically an example of a hapten?

Alum precipitated toxoid Signup and view all the answers

Which type of MHC molecule is found on all nucleated cells?

Class I Signup and view all the answers

What is the primary role of Class II MHC molecules?

Present antigens to CD4+ helper T cells Signup and view all the answers

Which HLA gene is associated with ankylosing spondylitis?

HLA-B27 Signup and view all the answers

Where are the genes that determine histocompatibility antigens located?

On the short arm of chromosome 6 Signup and view all the answers

Which class of MHC molecules is involved in the production of complement components?

Class III Signup and view all the answers

Which MHC molecules complex with peptides and present antigens to CD8+ cytotoxic T cells?

Class I Signup and view all the answers

Which region on the short arm of chromosome 6 determines the antigenic specificity of Class II MHC molecules?

Region D Signup and view all the answers

Which of the following cells recognize antigens only when associated with Class II MHC molecules?

CD4+ helper T cells Signup and view all the answers

Which of the following terms is used to describe antibodies directed against an individual's own proteins?

Autoantibodies Signup and view all the answers

What is an important characteristic of the innate immune system?

It is present at birth and always active Signup and view all the answers

What is the role of heterophile antibodies in the Paul Bunnel Test?

To agglutinate sheep or horse RBCs Signup and view all the answers

Which molecule on the surface of most gram-negative bacteria is recognized by the innate immune system?

LPS Signup and view all the answers

What is the main defense function of intact skin and respiratory tract?

Blocking microbial entry Signup and view all the answers

In the context of the immune system, what is known as cross-reactivity?

Antigen binding to an antibody that was produced in response to partially related antigens Signup and view all the answers

What role does the innate immune system play in the adaptive immune response?

Stimulating the adaptive immune response Signup and view all the answers

Which of the following is an in-vivo example of cross-reactivity?

Acute rheumatic fever Signup and view all the answers

Study Notes

Antigens

Antigens are foreign substances that can stimulate the immune system
They can be proteins, polysaccharides, lipids, or nucleic acids
Epitopes or antigenic determinants are specific small parts of the antigenic molecules that can stimulate the immune system

Epitopes or Antigenic Determinants

The number of epitopes on a molecule varies with molecular size
For example, human albumin has at least six different epitopes, which means that at least six different antibodies can be produced after immunization

Factors Influencing Antigenicity

Foreignness: The immune system can distinguish between self and non-self, and only foreign substances can stimulate an immune response
Molecular size: Small molecules are usually not immunogenic, while larger molecules can be antigenic
Chemical nature: Proteins are the most potent antigens, while some polysaccharides of high molecular weight can be antigenic
Methods of administration: The dosage, frequency, and route of administration of antigens can influence the immune response

Adjuvants

Adjuvants are substances that can enhance the immune response when mixed with an antigen
Examples of adjuvants include aluminum phosphate, alum precipitated, and diphtheria toxoid

Haptens

Haptens are substances that are not immunogenic by themselves but can become immunogenic when coupled to a carrier molecule
Examples of haptens include neomycin, skin ointments, and cosmetics

Types of Antigens

Bacterial antigens
Viral antigens
Human tissue antigens (e.g., blood group antigens, histocompatibility antigens)

Human Tissue Antigens

Blood group antigens: A and B antigens on red cells, important in blood transfusion reactions
Histocompatibility antigens: Present on the membrane of tissue cells, also known as major histocompatibility complex (MHC) antigens or human leukocyte antigens (HLA)

Histocompatibility Antigens

Definition: Molecules present on the membrane of tissue cells that can stimulate an immune response
Types: Class I, II, and III MHC antigens
Class I: Present on all nucleated cells
Class II: Present on antigen-presenting cells (APCs) such as B cells, macrophages, and dendritic cells
Class III: Involved in the production of complement components

MHC Significance

Organ transplantation and rejection: MHC antigens play a crucial role in organ transplantation and rejection
MHC restriction: Th cells recognize peptide antigens on the surface of APCs only when presented with MHC class II molecules, while Tc cells recognize antigens on the surface of virus-infected cells or tumor cells only when presented with MHC class I molecules
Paternity testing and forensic medicine: MHC antigens can be used to determine paternity and in forensic investigations
Disease association: Certain MHC antigens are associated with specific diseases, such as HLA-B27 with ankylosing spondylitis and HLA-DR4 with rheumatoid arthritis

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Description

Learn about antigens, their composition, and epitopes, the specific parts of antigens that stimulate the immune system.