Immunology

Question 1

Define an Antibody (Ab) ?

Answer 1

An immunoglobulin (Ig), is a large, Y-shaped protein produced mainly by B lymphocytes of the immune system

Question 2

Define an Antigen (Ag) ?

Answer 2

A substance that induces an immune response e.g. antibodies

Question 3

Define Epitope ?

Answer 3

Part of the antigen that the antibody attaches it self to

Question 4

Define Immunoassay/assay ?

Answer 4

A procedure for detecting or measuring specific proteins or other substances through their properties as antigens or antibodies

Question 5

Define Serology/serological assay ?

Answer 5

The scientific study or diagnostic examination of blood serum

Question 6

Define Analyte ?

Answer 6

The molecule being measured in the assay

Question 7

Define Enzyme-linked immunosorbent assay (ELISA) ?

Answer 7

A quantitative immunological assay used to measure proteins such as antibodies and antigens

Question 8

Define Monoclonal antibodies ?

Answer 8

Antibodies that are made by identical immune cells that are all clones of a unique parent B cell

Question 9

Define Polyclonal antibodies ?

Answer 9

Antibodies that are secreted by different B cell lineages within the body

Question 10

What is the membrane bound for antibodies ?

Answer 10

Known as Immunoglobulin or B cell receptor (BCR)

Question 11

What can the Variable Region and the constant region also be called ?

Answer 11

Variable Region= Fab region

Constant region= Fc region

Question 12

What are examples of antigens ?

Answer 12

Can be pathogen components, proteins, carbohydrates, lipids, drugs, toxins…etc

Question 13

Monoclonal vs. Polyclonal antibodies ?

Answer 13

• Highly specific for corresponding antigen, detect 1 epitope out of >108
• Easy to isolate & study. Invaluable as probes of biological processes
• Have different Isotypes (Ab class) conferring diverse functions
• Can be generated in large amounts
• Have high Affinity for their antigen

Question 14

What does the antibody affinity constant affect ?

Answer 14

Sensitivity

Question 15

What is avidity ?

Answer 15

The total strength of the interaction

Question 16

How is the affinity measured ?

Answer 16

AFFINITY is measured by KD - equilibrium dissociation constant

Question 17

ELISA has ?

Answer 17

High sensitivity, but not necessarily high specificity

Question 18

What does ELISA diagnose?

Answer 18

Diagnosis of HIV infection, pregnancy tests, measurement of cytokines or soluble receptors in cell supernatant or serum

Question 19

ELISA assays are generally carried out in ? allowing ?

Answer 19

ELISA assays are generally carried out in 96 well plates, allowing multiple samples to be measured in a single experiment.

Question 20

Explain the Indirect ELISA practical ?

Answer 20

• Microwell plates are incubated with antigens, washed (to remove unbound) and blocked with BSA
• Samples and controls are added and incubated
• Plates are washed and then an enzyme-linked secondary antibody is added and plate washed
• Substrate is added and enzymes on the antibody elicit a colourometric change

Question 21

What does a Positive control confirm ?

Answer 21

It confirms the assay is working and is specific

Question 22

What does a Negative control confirm ?

Answer 22

It confirms a positive result is not due to non-specific binding of Abs or faulty reagents or any other reason

Question 23

Each negative control has one vital step removed:

Answer 23

1. NO antigen (BSA)
2. NO primary antibody
3. NO Labelled detection/secondary Ab
4. NO Substrate

Question 24

What is Analytical Sensitivity ?

Answer 24

– ability of a test to detect very small amounts of Ag or Ab

Question 25

What is Clinical Sensitivity?

Answer 25

– ability of test to give positive result if patient has the disease (no false negative results)

Question 26

Explain a False negative ?

Answer 26

– the test result is negative, as the concentration of the measured Ab or Ag is too low for detection (sensitivity). In reality, the patient has the disease and the test result should be positive

Question 27

What is Analytical Specificity ?

Answer 27

– ability of test to detect substance without interference from cross-reacting substances

Question 28

What is Clinical Specificity?

Answer 28

– ability of test to give a negative result if patient does not have disease (no false positive results)

Question 29

Explain a False positive ?

Answer 29

– the test result is positive, as the test is detecting another cross-reacting substance. In reality, the test result should be negative as the patient does have the disease