The Immune System: an introduction

Question 1

What is an immune system?

Answer 1

a system of cells, tissues and their soluble products that recognises, attacks and destroys foreign entities that endanger the health of an individual.

Question 2

What are extracellular pathogens?

Answer 2

Do not need to enter the host’s cells to replicate. they can replicate in the interstitial fluid and disseminate via the blood
-Bacteria and Parasites

Question 3

What are intracellular pathogens?

Answer 3

Need to enter the host’s cells to replicate. these pathogens hijack the cellular metabolic machinery for their own replication and disseminate via the blood.
-Viruses, bacteria and parasites

Question 4

What is the innate immune response?

Answer 4

initial response to pathogens’ penetration

• always involved
• fast
• non specific
• mediated by the skin and the acidic stomach and lysozymes in the saliva and tears and mucus
• mediated my leukocytes and the complement

Question 5

What is the adaptive response?

Answer 5

if the innate response is unable to block the spread of the pathogen it is activated

• only activated as needed
• slow
• highly selective

Question 6

What is a lysozyme?

Answer 6

a secreted enzyme that hydrolyses the bacterial wall and causes the lysis of the pathogenic bacteria

Question 7

What is PAMP?

Answer 7

pathogen associated molecular pattern
-molecules present in the pathogen but absent in the host: so this allows the innate immune system to identify the non-self

Question 8

What is the leukocyte-mediated innate response?

Answer 8

-Leukocytes have pattern recognition receptors (PRRs) that recognise PAMPs on pathogens
-Once the PRRs bind to the PAMPs, the leukocytes are activated and initiate destruction of the pathogen:
-phagocytosis
-Target cell lysis
-inflammation
Cells involved:
-T and B lymphocytes
-Dendritic cells

Question 9

What are chemokines?

Answer 9

signal the area the inflammation and immune cells equipped with receptor for the chemokines migrate to the infected areas

Question 10

What are cytokines?

Answer 10

stimulate activation of the immune cells

Question 11

What is an antigen?

Answer 11

a foreign molecule which induces and immune response in the body especially, but not only, the production of antibodies

Question 12

What is epitope?

Answer 12

the portion of the antigen that is recognised by the lymphocytes, typically is a peptide of 12-15 amino acids

Question 13

What is MHC?

Answer 13

major histocompatibility complex

Question 14

How is a MHC formed?

Answer 14

• external pathogens are internalised by phagocytosis
• then they are digested by a complex endocytic process
• digested peptides of the pathogen are loaded onto the MHC-II and exposed on the membrane

Question 15

How are B lymphocytes activated?

Answer 15

• The pathogen is phagocytosed
• it is broken down by lysozymes within the cell
• the antigens present on the pathogen are presented on the APC
• the helper T lymphocyte binds to the APC and secretes cytokines

Question 16

When B cells proliferate and generate daughter cells what are they called?

Answer 16

plasma cells

Question 17

How are intracellular pathogens eliminated?

Answer 17

• any infected cells in the body expose the antigens using MHC-I
• cytotoxic T-lymphocytes recognise the infected cells using the MHC/TCR interaction
• Cytotoxic T-lymphocytes kill the infected cells
• recognise and KILL