Immunology

Question 1

4 key characteristics of an immune response

Answer 1

a) Detection of pathogens/infection
b) Clearance of pathogens/infection
c) Self-regulation
d) Protective immunity against recurrent disease

Question 2

First line defence systems

Answer 2

. Epithelial layers connected by tight junctions are constant in this regions and act as a first line mechanical barrier. Other mechanical barrier include the movement of cilia in the nasal passages and lungs which move external material which has entered into the lumen back towards the external environment, the longitudinal flow of air in the lungs which also pushes foreign matter back out of the external environment or the formation of tears when foreign matter gets into the eyes, which again serves to flush out any foreign matter.

Chemical defences include the low pH environment of the stomach and enzymes found in the tears (lysosome) or gut (i.e pepsinogen) which breakdown any pathogenic material. Antibacterial peptides are also present at all interfaces.

Microbiological barriers are the normal flora found in all of these regions.

Question 3

a) Natural Killer cells:

Answer 3

These destroy foreign or altered self-cells. Normal cells express MHC I molecules which bind to the inhibitory receptor on NK cells. If this MHCI receptor is altered or not expressed as is the case in infected cells, NK cells will release cytotoxic granules onto the infected cells thereby inducing apoptosis in the cells.

Question 4

b) Neutrophils

Answer 4

These are phagocytic cells. They travel around in the blood and are the first immune cell recruited to the site of infection or inflammation. They engulf extracellular pathogens into phagosomes and destroy the pathogen with enzyme granules and reactive oxygen species.

Question 5

c) Macrophages

Answer 5

Macrophages are also phagocytic cells. They are found in tissues throughout the body. They serve an important role in the development of an immune response as after pathogen engulfment they release cytokines (i.e. IL-1, IL-6 and TNF-) to promote the recruitment of other immune cells to the site of infection. Macrophages also act as antigen presenting cells thereby act as a bridge between innate and adaptive immunity.

Question 6

d) Dendritic cells

Answer 6

Dendritic cells are also phagocytes. These are “professional” APC as they travel in the blood throughout the body and hence are more effective at patrolling for pathogens.

Question 7

e) Eosinophils

Answer 7

Eosinophils handle large, multicellular parasites which are too large to undergo phagocytosis. They bind to the surface and release cytotoxic granules directly onto the cell surface.

Question 8

Humoral components of the immune system

Answer 8

Complement : Opsonization Lysis of pathogens
Capillary dilation Recruitment and activation of phagocytic cells

Coagulation:Increase in vascular permeability
Lactoferrin and transferrin : Compete with bacteria for iron
Lysozyme :Break down bacterial cell walls
cytokines:Various roles

Question 9

How complement works and its role in the immune system

Answer 9

The complement system is an amplification cascade which promotes the development of an immune/inflammatory response. The complement system consists of 20 or so different proteins found in the blood and are produced by a variety of cells such as hepatocytes, macrophages and gut epithelial cells. Complement proteins bind to the surface of proteins and then act via a proteolytic cascade to amplify the signal.

An exemplar pathway is activated C1 being cleaved to become a serine/threonine protease. This catalyses a sequence of downstream reactions resulting in the formation of complement 3b and 3a.

 Lysis of bacteria
 Opsonising bacteria for enhanced phagocytosis
 Recruitment and activation of phagocytic cells
 Regulating antibody responses
 Removal of immune complexes and phagocytic cells.