L4 Host immune responses

Question 1

What are the main goals of innate and aquired immune response>

Answer 1

innate - to prevent infection

aquired - prevent establishment, secondarily establishment and to remove parasites

Question 2

Where are B and T cells made and where are they found?

Answer 2

B cells - mammals- bone marrow, birds- Bursa of fabricius. Stem cells in bone marrow give rise to immune cells.
T cells - Thymus dependent
Concentrated in secondary lymphoid organs eg lymph nodes and spleen.

Question 3

How do B cells function

Answer 3

Produce immunoglobins - specific to epitope of antigens and recognise antigens.
Binds to antigen epitope, can be several epitopes, but only 1 is recognised specifically.
Once bound, stimulates B cell to proliferate, forming memory cells and plasma cells to release Ig.
Somatic recombination of genes coding for components of Ig allows each B cell clone to produce antibody with unique specifity.

Also, present MHC2 from engulfed antigen on the surface, T helper cell recognises, causing B cell to proliferate.

Question 4

Ig structure

Answer 4

consists of 4 chains, 2 long, 2 short.

Constant and variable region.

Question 5

Ig types

Answer 5

IgA - dimer, in mucus membranes
IgM - pentameric, first to be produced in immune response
IgG - Dominant in circulation.
IgE - inflammation
IgD- ?

Question 6

vaccination…

Answer 6

induces a primary immune response so when a real infection is caught, a secondary response is generated.

Question 7

4 functions of antibodies

Answer 7

1. Directly interferes with antigen action.
2. activate complement
3. Attract cells to release cytotoxic molecules [ADCC antibody dependent cell-mediated cytotoxicity]
4. coats antigen to facilitate phagocytosis

Question 8

What is the complement cascade?

Answer 8

Cascade of soluble molecules in circulation, brought together and starts cascade by binding of Ig to antigen/pathogen.
Activated complement forms pores in membrane , killing invading cells and attracting inflammatory cells.

Question 9

What is MHC?

Answer 9

differentiates self from non self.
only individuals with close MHC types will be considered for transplants. Immunosupressive drugs needed.
Large genetic locus - HLA locus, Human leucocyte antigen
All humans have a unique molecular signature defined by MHC.

Question 10

Whats the difference between MHC class 1 and 2?

Answer 10

MHC class 1 - define self
MHC class 2 - specific to immunological cells

Question 11

What defines T helper cells

T cytotoxic cells

Answer 11

Th - Molecularly defined by presence of CD4.
Tc - presence of CD8 marker.
CD8 and CD4 cells ratio are used in assessing HIV infection and therapy.

Question 12

3 functions of Th cells

Answer 12

• Help other parts of the immune system to act
• T helper recognises molecules in presence of MHC class 2 molecules presented by B cells, causing them to proliferate.
• Cytokines released by Th to signal to B cell.

Question 13

2 types of Th cells

Answer 13

Th 1 - cell mediated immunity, antimicrobials, intracellular parasites
TH2 - proinflammatry, anti macroparasite/helminth

Question 14

What is the hygeine hypothesis?

Answer 14

Historically, people have a balance between Th1 and Th2. Now, in developed countries people have more Th1 due to less parasite exposure. Greater Th2 responsiveness, may become overactive, and more risk of allergies and worms.
In developing countries people more exposed to bacterial and viral infection so have greater Th1 responsiveness.

Question 15

What is an effect of IgE?

Answer 15

IgE is involved in the inflammatory response, and allergic reactions.
Type 1 sensitivity causes thee release of histamines from mast cells. 5 types of hypersensitivity

Question 16

What do Cytotoxic T cells do?

Answer 16

Kill target cells with foreign antigen on surface

Causes release of perforin creating lesions in target membrane.