Exam Questions

Question 1

What are combined immunodeficiencies

Answer 1

Result from an absence of T cells, or impaired T cell function, combined with some disruption of antibody response

Question 2

Write a note on X-Linked Agammaglobulinemia
(6)

Answer 2

Originally called Bruton’s agammaglobulinemia

Patients have extremely low Ab levels

Babies born with this have virtually no B cells in peripheral blood

Suffer from recurrent bacterial infections

It is caused by a defect in the gene coding for the enzyme Bruton’s tyrosine kinase (Btk) which is involved in B cell development

Developing cells in the basal membrane are arrested at the pre-BCR stage

Question 3

Write a note on leucocyte adhesion deficiency
(4)

Answer 3

LADI is caused by a mutation in the CD18 gene

CD18 is the B chain of B2 integrins that include CR3. CR4 and LFA-1, all vital for the adhesion cascade

As CR3 and CR4 also function in the complement system phagocytes are unable to engulf microbes opsonised by C3b and C4b

Patients display omphalitis, gingivitis and recurrent infections

Question 4

What is the role of the clinical immunology laboratory in the diagnosis of primary immunodeficiency
(6)

Answer 4

Detection of autoantibodies -> ELISA, immunofluorescence (direct and indirect)

Measurement of antibody levels - nephelometry

Measurement of specific antibody responses -> vaccination and allergy

Monitoring of serum proteins e.g. monoclonal gammopathy via serum protein electrophoresis

Measurement of complement levels/function - nephelometry, CH50, CH100 and AP50 assays

Leukocyte number/functions - flow cytometry

Question 5

What are the principles of nephelometry
(3)

Answer 5

Add anti-sera for protein of interest (e.g. antibodies, C3, C4 and C1 inhibitor)

Where immune complexes form they will scatter light which can be detected

Standards can be used to calculate the concentration

Question 6

What is the principle of serum protein electrophoresis?
(3)

Answer 6

Electrophoresis is a method of separating proteins based on their physical properties

Serum is placed on a specific medium, and a charge is applied

The net charge (positive or negative) and the size and shape of the protein are used to separate and differentiate the various serum proteins

Question 7

What is the principle of flow cytometry?

Answer 7

Flow cytometry is a technique for counting, examining and sorting microscopic particles suspended in a stream of fluid

Physical characteristics, size and granularity of particles are measured while fluorescently labelled antibodies can be used to examine protein expression

A laser beam is directed at a hydro-dynamically focused stream of fluid containing the cells in single cell suspension

A number of detectors measure properties such as forward scatter(size), side scatter (granularity) and fluorescence (specific protein expression) at different wavelengths

Question 8

List the order of cells involved in inflammation
(6)

Answer 8

Mast cell -> Gatekeeper

Neutrophil

Monocyte -> macrophage

Dendritic Cells

T cells

Helper T cells

Question 9

Write a note on macrophages
(4)

Answer 9

Big Eater

Phagocytose

Release chemokines (CXCL-8)

Release pro-inflammatory cytokines

Question 10

Write a note on the functions of mast cells
(4)

Answer 10

releases histamine and cytokines e.g. IL-8
o Vasodilation in response to histamine -> more blood -> more wbcs
o Increased vascular permeability
o Increased expression of adhesion molecules -> allow for adhesion cascade

Question 11

How are mast cells activated
(4)

Answer 11

By allergens through cross linking with immunoglobulin E receptors (e.g., FcεRI),

By Physical injury through pattern recognition receptors for damage-associated molecular patterns (DAMPs)

By microbial pathogens through pattern recognition receptors for pathogen-associated molecular patterns (PAMPs),

Complement proteins can activate membrane receptors on mast cells to exert various functions as well

Question 12

What do anaphylotoxins do?

Answer 12

Activate basophils and mast cells to degranulate resulting in increased vascular permeability and contraction of smooth muscle cells

Question 13

List the anaphylatoxins

Answer 13

C5a
C4a
C3a

Question 14

What are the functions of anaphylatoxins
(4)

Answer 14

Degranulation of mast cells
Smooth muscle contraction
Increased vascular permeability
C5a causes chemotaxis of leukocytes

Question 15

What is the CH50 assay used for?

Answer 15

It demonstrates the ability of serum complement to lyse sheep RBCs coated with antibody

Question 16

How does the Mannose binding lectin pathway work?
(4)

Answer 16

MBL attaches to mannose/frucose containing polysaccharides on bacteria

MBL is then bound by MASP-1 and MASP-2

MBL associated serine proteases

MASP cleaves C2 and C4

Question 17

How is the classical pathway activated
(3)

Answer 17

Complement fixation

Activated by IgM and IgG

Complement binds to the CH2 domain of these

Question 18

How do complement proteins act as opsins
(3)

Answer 18

Complement proteins bind to pathogens and mark them for phagocytosis

The phagocytes express receptors such as CR1 which allows the cell to recognise complement attached to a pathogen

When the receptor meets the complement there is a conformational change and the pathogen is phagocytosed

Question 19

How does complement activate the inflammatory response?

Answer 19

If complement binds to the receptors found on granulocytes it causes these cells to degranulate e.g. mast cells/gatekeeper cells releasing histamine causing inflammation and vasodilation

Question 20

How do complement proteins clear immune complexes

Answer 20

Complement marks antibody-antigen complexes for phagocytosis in the liver and spleen

Question 21

What are the four main functions of complement

Answer 21

Formation of MAC

Opsonisation

Disposal of immune complexes and apoptotic cells

Activation of immune responses e.g. vascular permeability, chemotaxis for phagocytes and degranulation

Question 22

Define the complement system

Answer 22

The complement system is a biological cascade made up of multiple serum proteins that is part of the innate immune system