Lecture 7

Question 1

What is hashimoto’s thyroiditis?

Answer 1

An autoimmune condition in which antibodies and cytotoxic cells destroy thyroid tissue and thyroid hormones

Question 2

What is pernicious anemia?

Answer 2

An autoimmune condition where antibodies damage parietal cells resulting in compromised vitamin B12 absorption

Question 3

What is systemic lupus erythematosus?

Answer 3

An autoimmune condition where there are antibodies against DNA and nuclear antigens, immune complexes which lodge in kidneys, joints and skin and complement mediated tissue damage

Question 4

What are the more important contextual aspects of immune recognition?

Answer 4

The nature of the antigen
Antigen concentration
Venue (mucosa, peripheral tissues, circulation, secondary lymphoid organs)
How antigen is processed
How antigen is presented to antigen-specific lymphocytes
What sort of receptors recognise the antigen
The individuals antigenic history
Associated soluble and cell-surface signalling events

Question 5

What are the specific receptors on B cells?

Answer 5

Immunoglobulin receptors which are very similar in structure to antibodies

Question 6

What are the specific receptors on T cells?

Answer 6

T cell receptors

Question 7

How does commitment of individual lymphocytes to particular receptor shapes occur?

Answer 7

Gene rearrangements

Question 8

What results from antigen recognition?

Answer 8

Lymphocyte activation, proliferation and/or differentiation
Generation of effector functions (phagocytosis, antibodies, cytotoxicity and inflammation)
Recruitment of non-specific effector mechanisims
Redistribution
Immunological memory

Question 9

How is responsiveness of the immune system controlled?

Answer 9

Cellular receptivity controlled by the type of receptor and the antigen
Presentation and recognition such as MHC presentation and likeness to self antigen
There are hormonal requirements

Question 10

Why are mechanisms for immune tolerance necessary?

Answer 10

The shape of the receptor that lymphocytes commit to is essentially random meaning that there must be some lymphocytes generated that recognize self-antigen these must be controlled to prevent the occurrence of autoimmune conditions

Question 11

What are epitopes?

Answer 11

While antigens have a large amount of variety in terms of their shapes and sizes the antigen-binding receptors on the surface of lymphocytes can only recognize and bind to structures of a certain size, these are termed antigenic determinants or epitopes

Question 12

Are the epitopes recognized by B cells and T cells the same?

Answer 12

No the B cell receptors come from on series of genes which is the same as that used to code antibodies therefore these can recognizes the same epitopes but T cell receptors use genes which are related to the B cell genes but are not the same causing the two lymphocytes to exist in different antigenic universes

Question 13

What are the intrinsic properties of protein antigens that influence immunogenicity?

Answer 13

Size with an increased size reflecting an increased immunogenicity
Composition with more complex antigens reflecting greater immunogenicity
Similarity to self-proteins where the larger the difference the grater immunogenicity
The interaction with the host MHC with an effective interaction resulting in increased immunogenicity

Question 14

What are the two ways in which antigenic epitope can be constructed?

Answer 14

They may be a result of a short linear sequence of amino acids within the polypeptide of the target (termed linear) or they might be due to two or more sort segments in the target which are brought together due to protein folding (termed assembled)

Question 15

What are the most common epitopes in immunology?

Answer 15

Proteins

Question 16

What is the typical size of antigenic epitopes on proteins?

Answer 16

These are generally between 5 and 20 amino acids

Question 17

What is the difference between B and T cells in terms of antigen recognition?

Answer 17

B cells are capable of recognition of both assembled and linear epitopes while T cells can only recognize linear epitopes, T cells also require large antigens to be processed into smaller fragments and presented to them

Question 18

What occurs when a foreign substance enters the body?

Answer 18

Phagocytic cells attempt to ingest it and destroy it
Antigens or antigenic fragments are transported to regional lymph nodes
Specialized antigen-presenting cells process antigen and present epitopes to antigen sensitive lymphocytes
Specific lymphocytes become activated and generate an immune response

Question 19

What are the functions of antigen presenting cells?

Answer 19

Antigen collection
Antigen concentration
Antigen processing
Antigen presentation
Co-stimulation through accessory surface molecules (B7 and CD28) and proinflammatory cytokines (like IL-1, IL-6 and TNF)
Tolerance induction

Question 20

What phagocytes are present at each site of antigen entry?

Answer 20

Langerhans cells are in the skin, these undergo lymphatic transport to regional node
Blood monocytes are present in the blood these transport antigen to the spleen or regional nodes
Alveolar macrophages are present in the lungs and transport antigen to the spleen or regional nodes
Kupffer cells are present in the liver and transport antigen to the spleen or regional nodes
Epithelial M cells are present in the gut and these transport antigen to peyer’s patches

Question 21

What is the sequence of events when antigen enters a lymph node?

Answer 21

Antigen enters the lymph node through afferent lymphatics and small naïve lymphocytes enter from the blood stream
T cells migrate to T cell areas of the node and B cells migrate to follicles
Lymphocytes that recognize the antigen stop recirculating and are activated lymphocytes that do not recognize antigen leave via the efferent lymphatic vessel
After several days activated lymphocytes leave the efferent lymphatic vessel as effector cells