18. Immunology (Acquired) Flashcards
What do antigens depend on? (2)
Depends on regularly recurring molecular groups (epitopes) on surface of the molecule
What are lymphocytes responsible for? Where is it? How is it distributed? (3)
- Lymphocytes are responsible for acquired
immunity - Located most extensively in special lymphoid tissue
- Lymph tissue is distributed in such a manner as to intercept organisms or toxins before they spread too widely
Explain how lymphocytes function in different parts of the body (3)
- In gastrointestinal tract: intercept antigens from gut
- Adenoids and tonsils: intercept antigens from upper respiratory tract
- Spleen ,thymus and bone marrow: Intercept antigens that have succeeded in entering the general circulation
T-lymphocytes vs B-lymphocytes
- T-lymphocytes: Responsible for forming the activated lymphocytes that provide ‘cell-mediated’ immunity
- B-lymphocytes: Responsible for forming antibodies that provide humoral immunity
Explain T-lymphocytes (6)
- Form in bone marrow
- Divide rapidly in thymus
- Develop extreme diversity for reacting against different specific antigens
- Spread via blood to lymphoid tissue everywhere
- Before leaving the thymus the T-lymphocytes are mixed with all the ‘self-antigens’ from body tissue – if it reacts the T-lymphocytes is destroyed
- Most done prior to birth and shortly after birth
Explain B-lymphocytes (4)
- Pre-processed in fetal liver and bone marrow
- Secrete antibodies that are reactive agents
- Have even greater diversity than T-lymphocytes
- Also move to lymphoid tissue (near but slightly removed from T-lymphocytes)
Explain the function of macrophages and its effect on B and T cells (5)
- When a foreign antigen enters:
- Macrophages in lymphoid tissue phagocytize the antigen and present it to the adjacent B and T lymphocytes
- The activated T-lymphocytes will produce helper T-cells which contribute to the activation of the B-lymphocytes
- The B-lymphocytes specific for the antigen presented enlarge and take on the appearance of a a lymphoblast – which further differentiates into plasmablasts which are the precursors of plasma cells (within 4 to 5 days have 500 cells
for each original plasmablast) - Then antibodies are secreted into lymph and carried to blood
Explain memory cells
- Some of the lymphoblasts form new B-lymphocytes rather than plasma cells
- These memory cells mean that the next time the animal is exposed to the same antigen the response is much more rapid and potent
- More rapid, more potent and more prolonged
Explain gammaglobulins-immunoglobulins (Iq) (3)
- Antibodies
- Combination of light and heavy chains
- Contains a variable and constant portion
Explain the variable portion of Ig
- Differs for each specificity or antibody
- Portion that attaches specifically to a
particular type of antigen
Explain the constant portion (5)
- Determines the biological properties
- Diffusion
- Adherence
- Attachment to complement complex
- Ease of passing through membranes
What are the classes of antibodies with general info (5)
- IgG – 75% of the antibodies of a normal animal
- IgE – small percentage – involved in allergy
- IgM – many binding sites per antibody
- IgA
- IgD
What are the actions of antibodies (7)
- Direct attack on the invader to inactivate the invading agent
- Agglutination
- Precipitation
- Neutralization ( cover the toxic site)
- Lysis - Direct actions generally not strong enough to elicit a strong response
- Activation of the complement system or complex
Explain the antigen-antibody reaction (3)
1.When the antibody binds the antigen – a specific reactive site in the ‘constant’ portion of the antibody is uncovered or activated
2. The activated site binds directly with the C1 molecule of the complement system
3. Activates C1 enzymes which activate successively increasing quantities of enzymes causing formation of many end products
Explain end products: opsonization and phagocytosis
Activates neutrophils and macrophages
Explain the function of the cell mediated system when exposed to specific antigens
- T-lymphocytes produce activated T-cells that are released into the circulation
- Also produce T-lymphocyte memory cells
- Therefore release of activated T cells occurs more rapidly and more powerfully on subsequent exposure to the same antigen
- T-lymphocytes only respond to antigens when the antigens are bound to specific molecules called MHC proteins
Explain the function of MHC proteins in cell-mediated immunity (3)
- MHC proteins are found on the surface of antigen presenting cells in the lymphoid tissue
- Antigen presenting cells include
* Macrophages
* B-lymphocytes
* Dendritic cells - Interaction of cell adhesion proteins is critical in permitting the T-cells to bind to antigen presenting cells long enough to
become active
What are the functions of cytotoxic T-cells/killer cells? (1)
Bind to antigen and secrete hole forming protein called perforins, then releases a cytotoxic substance directly into the attacked cell
