Innate and Adaptive immune system

Question 1

What is the innate immune system

Answer 1

First defence in the body, present at birth but contains no memory and no specificity and responds rapidly.

Question 2

What are the components of the innate immune system

Answer 2

1a) physical barrier- impermeable outer surface e.g. skin, epithelial cells.
b) cilia in nasal passages and bronchi
c) air borne bacteria are trapped on the mucus by goblet cells.

2) chemical barrier- acidity in the stomach- most pathogens are destroyed by the low pH of the stomach.
b) alkaline secretions
c) lysozyme in tears

3) biological barriers- competition with the commensal organisms

Question 3

What cells are involved in the innate immunity

Answer 3

phagocytes- moncytes, macrophages, neutrophils

natural killer cells- kill tumour and virally infected cells

eosinophils- attack and kill parasites

Question 4

What soluble factors are involved in the innate immunity

Answer 4

Lysozyme
complement- involves enzyme cascades
cytokines- particularly interferons
acute phase proteins

Question 5

What is the adaptive immune system

Answer 5

It is slow, has memory, highly specific, recognises between the self and non-self and is adaptive. It provides immunological memory.

Question 6

What are the two components of the adaptive immune system?

Answer 6

Humoral component

Cellular component

Question 7

Explain the two components of the adaptive immune system?

Answer 7

The humoral part has antibodies (immunoglobulins)- which are specific proteins that are produced against a pathogen. It is produced by B lymphocytes that stimulate plasma cells to produce antibodies.

Cellular component allow the recognition of antigens and is medicated by T lymphocytes. They have two components- the helper T cells which help B cells to produce antibodies. Cytotoxic T cells that kill their own cells that have been infected by the virus.

Question 8

What are the two roles of the immune system?

Answer 8

Recognition- antigen identification

effector- antibody production

Question 9

What is an antigen?

Answer 9

Antigen- this is any substance that elicits and immune response. The portion that is recognised is epitope or antigenic determinant.

Question 10

Describe an antibody?

Answer 10

Immunoglobulins have two identical heavy and light chains on each side.

Each heavy/light chain has a variable region towards the top and a constant region at the bottom- The variable region is the N terminus and the constant region is the C terminus.

Both the light and heavy chains are linked by disulphide bridges.

Question 11

What are the dual functions of antibodies

Answer 11

1) recognition function- binding to the antigen - Fab Arms

2) effector function- Fc molecules will produce effector molecules that will trigger the removal of foreign material.

Question 12

What are the two types of light chains

Answer 12

Lambda

Kappa

Question 13

Which globular domains do the light chains fold into

Answer 13

VL (variable light)

CL (constant light)

Question 14

What does the heavy chain determine?

Answer 14

The heavy chain determines the class of antibody:
IgG
IgA
IgM
IgE
IgD

Question 15

What are hypervariable loops/ CDRS?

CDR- complementary determining region

Answer 15

Because they are millions of different antigens, we need a system that can identify these different antigen molecules- if you look at the variable heavy (VH) and variable light (VL) domains- there are 3 areas of intense variability where the amino acid tends to be different from one antibody to another- we refer to these regions as hyper variable loops of CDRs as they form loops in the 3D structure or complementary determining parts which determines which antigen they bind.

CDR- used to determine which antibody binds to which antigen.

Question 16

Why are CDR’s important

Answer 16

This is because they form the antigen binding site. When the Vh and VL domains are paired, their 6 CDR’s create an antigen binding site. 3 in Vh and 3 in VL

Each antibody will have a slightly different amino acid sequence within each of these hyper-variable loops and these will adopt a different 3D structure for each antibody. Therefore each antibody has its own unique antigen binding site.

Question 17

Describe IgG

Answer 17

Most abundant in plasma
It is the only IgG class to cross the placenta and protect the child during the early stages of life.
It is the predominant antibody of the secondary response
It triggers complement and phagocytosis via Fc receptors.
4 globular domains

Question 18

Describe IgM

Answer 18

5 Y shaped units joined by a Joining chain (J) chain and disulphide bridges.
Only in plasma and secretions- molecule is too large to enter tissues.
10 binding sites for antigen- very good at agglutinating particles
very efficient at triggering complement
predominant antibody for primary response

Question 19

Describe IgA

Answer 19

Main antibody in seromucous secretion- FIRST MILK after baby is born
class of antibody first encountered by many invading bacteria and viruses.

Question 20

What are the subclasses of IgA

Answer 20

IgA1 and IgA2- these are monomeric and dimeric forms

serum IgA- monomeric

secretory IgA- dimeric and has an additional polypeptide (secretory component SC) that protects in harsh environment of secretion

It has 2 different sugar linkage

0 linked
N linked

That protect it from degradation

Question 21

Describe IgE

Answer 21

It contains 5 globular domains in each of its heavy chains . Lots of N linked oligosaccharides or sugars.

It has an effector function where it interacts with a high affinity receptor. expressed on mast cells and basophils with allergic responses.

Question 22

Describe IgD

Answer 22

Low concentration in serum

found on lymphocyte surfaces

Question 23

Effector molecules

Answer 23

Fc receptor are receptors that bind specifically to the Fc region of immunoglobulins.

Fc gamma receptor- IgG
Fc Alpha receptor- IgA
Fc epsalon receptor- IgE

Macrophages- IgG and IgA
Neutrophils- IgA and IgG
Basophils and Mast cells- IgE

Question 24

What does the binding of antibody-coated targets to the FcR on immune cells can result in

Answer 24

1) phagocytosis
2) release of activated oxygen species
3) release of inflammatory mediators e.g. histamine released from mast cells
4) enhanced antigen presentation
5) clearance of immune complexes

Question 25

How does a mast cell work

Answer 25

Allergens cause binding of receptor with a slow off rate- it will attach to the receptor for about 2 weeks. If the person is exposed to the allergen- receptors are cross-linked to the surface which will send a signal to the mast cell and causes a release of histamine.