Immunology

Question 1

Give some examples of the body’s exterior immune defences

Answer 1

Question 2

Name 3 differences between innate and adaptive immunity

Answer 2

Question 3

What is the hypothesis behind why developed countries have higher rates of allergic disorders (asthma, eczema, rhinitis) ?

Answer 3

The hygiene hypothesis - early and regular exposure to certain bacteria / parasites promotes immune homeostasis

Question 4

What is autoimmunity?
Caused by the breakdown of what process?
Name three autoimmune diseases and the tissues that are attacked

Answer 4

Autoimmunity - attack against self-proteins or tissues.
Breakdown of tolerance = autoimmunity

Multiple sclerosis - myelin sheath destruction
Crohn’s disease - gut epithelium
Rheumatoid arthritis - lining of the joints

Question 5

What is hypersensitivity?

Hypersensitivity reactions are classed as type I-IV. What are some examples of a type I hypersensitivity reaction?

What type of immunoglobulin are involve in type I?

Answer 5

Hypersensitivity - over-reaction to benign antigens

Type I - anaphylactic shock, hay fever, asthma, hives, food allergies, eczema, bee stings, drug allergies, animals, latex.

IgE mediated. Histamine is released.
Reactions happen quickly
Most allergies are IgE mediated type I hypersensitivity reactions

More about hypersensitivity reactions in year 2

Question 6

Which of the following cells are involved in innate immunity and which in adaptive immunity?

B cells
T cells
Phagocytes
Antibodies
Complement 
NK cells
Dendritic cells

Answer 6

Question 7

What are the primary lymphoid organs and their functions?

Answer 7

Lymphoid organs produce lymphocytes.

Bone marrow - B cells.

Thymus gland - T cells. Where T lymphocytes mature. Thymus is located behind the sternum, it is large during childhood and puberty and shrinks in adults.

Question 8

What are the secondary lymphoid organs and their function?

Answer 8

Spleen, Tonsils, adenoids, appendix, lymph nodes, Peyer’s patches, MALT (mucosa associated lymphoid tissue)

Mature lymphocytes meet pathogens

Question 9

Summarise the process of phagocytosis. Which cells do this?

Answer 9

Macrophages - ingestion and destruction of particles / microbes

Question 10

What are the common types of antigen presenting cell?

Answer 10

Dendritic cell
Macrophage
B cell
Monocytes

MHC class II

Question 11

What is the difference between MHC class I and II

Answer 11

MHC class I molecules present antigens from inside the cell (endogenous pathway)
Found on all nucleated cells 

MHC class II molecules present antigens from outside the cell (exogenous pathway) 
Found on antigen presenting cells

Question 12

What is antigen presentation

Answer 12

Antigen presenting cells eg. Dendritic cells engulf and destroy pathogen, then present antigen to CD4+ T helper cell

Question 13

By what process and where are immune cells generated?

Answer 13

Immune cells are generated via haematopoiesis in the bone marrow

Question 14

What cells do lymphoid progenitor cells differentiate into?

Answer 14

B lymphocytes → plasma cells
T lymphocytes
NK cells

Question 15

What cells to myeloid progenitor cells differentiate into

Answer 15

End products - platelets, red blood cells, monocytes, granulocytes (neutrophils, basophils, eosinophils)

Question 16

What does a megakaryocyte produce?

Answer 16

Platelets

Megakaryocyte - Large cell. Big lobulated nucleus. Derived from myeloid stem cell. Produces platelets.

Question 17

What are reticulocytes?

In what clinical scenario would reticulocytes be high

Answer 17

Reticulocytes are immature red blood cells

Higher proportion of reticulocytes to mature blood cells means bone marrow is rapidly creating blood cells - reticulocytes are high in acute blood loss, or haemolysis where blood cells are being broken down

Question 18

What is the function of macrophages?

What cell are they derived from

Answer 18

Derived from monocytes

Macrophages are large cells with a single nucleus that ingest pathogens.
Monocytes circulate in the blood, then migrate to tissues where they differentiate into macrophages.

Macrophages:

• In most tissues
• first line of defence
• recognise PAMPs (pathogen associate molecular patterns)
• destroy pathogens using phagocytosis
• secrete cytokines that initiate the inflammatory response

Question 19

1 Function and 2 characteristics of neutrophils

Answer 19

Neutrophils

• circulate in the blood stream
• migrate to areas of inflammation due to signals (eg IL-8) from macrophages
• destroy pathogens by phagocytosis

Characteristics

• multi-lobed nucleus
• smallest granulocyte
• first white blood cell on the scene
• major constituent of pus
• most abundant white blood cell type
• cytoplasm contains a lot of granules including lysozyme, collagenase and other enzymes

Question 20

1 function and 2 characteristics of eosinophils

Answer 20

Function
- kills parasites (useful when pathogens are too large to undergo phagocytosis). Wait in tissues until activated by cytokines or respond to invading pathogen.

Characteristics

• red coloured cytoplasm under microscope (eosinophil = eosin loving. Eosin is a pink dye)
• bi-lobed nucleus
• Granules toxic to parasites that are released during degranulation such as ‘major basic protein’ that digests parasites
• circulate in the blood
• also capable of phagocytosis, to lesser extent than neutrophils and macrophages

Question 21

How are mast cells and basophils

1. Similar?
2. Different?

Answer 21

These cells have similar functions and were once thought to be the same cell

Both

• contain cytoplasmic granules that contain cytokines
• release histamine and play a role in allergic response eg increases blood vessel permeability
• both contain heparin

Mast cells

• fixed in place in the tissues
• round nucleus

Basophils

• circulate in the blood
• also play a role in parasite destruction like eosinophils
• lobed nucleus

Question 22

B lymphocytes mature where?

What do they have on their surface?

What two types of cell does it differentiate into? And what are their functions

Answer 22

Mature in the Bone marrow. B = bone.

Have antibodies (immunoglobulins) on the surface - specific to a single antigen/pathogen

Once activated by the antigen it differentiates into either plasma cells or memory B cells

Plasma cells make antibodies

Memory B cells await future infections

Question 23

T lymphycytes - where do they mature?

What do they have on their surface? What are the two groups?

Answer 23

T lymphocytes leave the bone marrow as ‘pro-thymocytes’ and travel to the thymus gland where they mature into T cells.

Mature in the thymus

Have T-cell receptors on their surface, specific to a single antigen. Two groups - CD4 receptors displayed by CD4 cells, CD8 receptors displayed by CD8 cells.

Note - FAS pathway causes apoptosis

Question 24

Natural killer cells - how are they different to T cells?

Answer 24

Recognise infected or abnormal cells without needing MHC receptors.

NK cells are different to T cells because they can detect cells that aren’t displaying MHC, allowing for a faster immune reaction. They were named ‘natural killers’ because they don’t need activation to kill cells that are missing the ‘self’ markers of MHC I. This is important because T cells cannot detect cells missing MHC I markers.

If the MHC I is absent, or foreign like in an organ transplant, the natural killer cell will kill the target cell.

Kill cells by releasing cytotoxic granules, induce cell death by apoptosis.

Also secretes interferon-Gamma that further activates macrophages and increases inflammatory response.

Question 25

Function of dendritic cells?

Answer 25

• Take up antigens
• Travel to lymph nodes
• Present antigen to CD4 or CD8 cells

Dendritic cells can activate both memory and naive T cells, and B cells.

Dendritic cells are the most potent antigen presenting cell
Have long dendrites that expand the surface area for finding lymphocytes

Question 26

What are Langerhans cells?

Answer 26

Specialist dendritic cells found in the skin