Lecture 1: organs of immune system

Question 1

What are the primary lymphoid organs

What are the secondary lymphoid organs

Answer 1

Bone marrow
Thymus

(produce immune cells (BM) and processed via maturation (thymus))

Skin
Mucous membranes
Bowel
Lymph nodes
Spleen
Tonsils

(in these organs, the cells do their work to fight infections)

Question 2

Role of thymus

Answer 2

Educates T cells

Question 3

T cell maturation/education

Answer 3

• T cells are made in the bone marrow, then migrate to the thymus
• In the thymus, they are called “thymocytes”
• Thymocytes undergo proliferation with rearrangement of genes to produce different T cells with an enormous range of different receptors, recognising different epitopes
• Of all the T cells made, only about 10% enter the circulation
• The ones that survive are those which can recognise different epitopes
• Those recognising the same epitopes, or self-epitopes are destroyed

Question 4

Thymic involution

Answer 4

Is proportional to thymic size, thymic activity and is most active BEFORE puberty

Question 5

Purpose of SKIN

Answer 5

Physical barrier

Question 6

purpose of mucous membrane

Answer 6

These line the respiratory, reproductive and digestive tracts

Mucous is a physical barrier, preventing many pathogens from gaining access to their target cells in the human

The bowel has the largest area of mucous membranes. Also contains lymphoid tissue called Peyer’s Patches

Question 7

Role of lymph nodes

Answer 7

• These are small oval structures in a network that contain lymph fluid
• They act as filters; filtering out harmful substances and draining them into the circulatory system for removal in spleen.
• They contain immune cells

Question 8

Role of spleen

Answer 8

Large organ which is a major reservoir for B lymphocytes and therefore a major site of antibody production

Question 9

Role of tonsils

Answer 9

In the throat, so can respond to pathogens at the point of entry to the body through ingestion or inhalation
* Contain lots of lymphocytes

Question 10

The immune response circle flow

Answer 10

1. pathogen challenge
   2.Recog
   3.Phagocytosis
   4.Cytokine release
   5.Inflammation
   6.Cessiation of innate immune response
2. Adaptive immune system start

Question 11

Innate immune responses
Step 1. Recognition

Answer 11

Cells of the innate system bind directly to pathogenic organism using pattern recognition receptors (PRR)
* These organisms display PAMPs (pathogen associated molecular patterns)
* The pattern recognition receptor on the cell binds to the PAMP

Question 12

Cells of innate immune system

Answer 12

• Phagocytes
• Macrophages
• Monocytes
• Neutrophils,basophils,
  eosinophils
• Dendriticcells
• Natural killer cells

Question 13

PAMPS and macrophages

Answer 13

Macrophages possess numerous receptors that allow direct recognition of particles based upon novel sugars, lipids, protein sequences and concentrations of charge that are unique to microbes:

so-called Pathogen-Associated Molecular Patterns or PAMPs

Question 14

Innate Immune response. Step 2 Phagocytosis

Answer 14

Phagocytosis: a cell extends pseudopodia and draws the pathogen inside itself; into a vacuole of its cytoplasm
* Lysozymes of the phagocytic cell digest the pathogen

Question 15

Process of phagocytosis

Answer 15

Phagosome
After engulfment, microbes are enclosed in a membrane vesicle derived from the plasma membrane of the cell

Phagolysosome
Membranes of the phagosome and lysosomes fuse resulting in a digestive vacuole called the phagolysosome.

Killing
It is within the phagolysosome that killing and digestion of the engulfed microbes by lysozymes takes place

Question 16

Opsonization:
what is opsonin and role of it

Answer 16

• An opsonin is any molecule that enhances phagocytosis by marking an antigen for an immune response.
• The opsonin helps the immune system recognise the pathogen target.
• Opsonins include mannose binding lectin (MBL) and complement.

Question 17

Innate immune responses
Step 3. Cytokines and define and example
Role of cytokines

Answer 17

Upon phagocytosis of a pathogen, cells release cytokines
* A cytokine is a chemical messenger that regulates cell differentiation and proliferation.

• interleukin-1: promotes the release of neutrophils from the bone marrow

The cytokines start the inflammatory process

Question 18

Innate immune response. Step 4 Inflammation

Answer 18

• Upon receiving a cytokine signal from infected cells, mast cells release histamine
• Histamine opens the capillaries to make it easier for the immune cells to leave the blood stream and attack the pathogen in the tissues
• We feel this as redness and soreness and HEAT at the wound site

Question 19

purpose of fever

Answer 19

• Fever (temperature rise) is a systemic response that assists the immune response by trying to kill the pathogens
• It is harder for pathogens to survive at higher temperatures

Question 20

Microbial Invasion of Pathogens

Answer 20

1. Pathogens can evade the immune system by growing in areas where there are no phagocytes (e.g. unbroken skin)

2.Pathogens can “trick” the immune system into thinking the bacteria are “self” cells

3. Bacteria can produce proteins that allow the bacteria to block phagocytosis or resist lysis once inside the phagocyte

4.Additional bacterial evasion mechanisms include inhibiting formation of the phagolysosome and impairing cytokine signaling

Question 21

Example of Microbial Invasion of Pathogens

Answer 21

Streptococcus pneumoniae “hides” its PAMPs within a capsule, preventing recognition and binding by phagocytic cells

Question 22

Natural killer cells function and what do they kill

Answer 22

NKC are very good at killing viral-infected cells and cancerous cells

• They are called “natural” because they are part of the innate system, able to recognise foreign cells without antigen-priming which cells of the adaptive system require
• They roam the body,constantly contact other immune cells, and become active when cytokines are released
• They kill by releasing cytotoxic contents onto the virus or cancer cell

Question 23

Complement purpose and example

Answer 23

The binding of mannose binding lectin, or pattern recognition receptors, can also activate complement

• Complement is a series of proteins C1 to C9 which activate in a cascade
• To form a membrane attack complex which causes the pathogen cell to burst