😀 EASY

A mixture of MCQs and short answer questions on some of the fundamental molecules, cells and stages of immune responses.

Reviewed by Daniel Mercer on 14th October 2019

Introduction to immunology

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Question 1
What is the largest immunoglobulin molecule?
A
IgA
B
IgD
C
IgE
D
IgE
E
IgM
Question 1 Explanation: 
IgM consists of five immunoglobulins joined together by a J chain
Question 2
Haemolytic disease of the foetus and newborn (HDFN, previously known as Rhesus disease) is a condition where a mother's antibodies attack the blood cells of her unborn baby causing them to be destroyed. The antibodies detect antigens that determine whether the baby's blood group is 'negative' or 'positive' but they don't react against the antigens that determine someone's ABO blood grouping - these latter antibodies cannot cross the placenta. Based on these observations, which types of immunoglobulins respectively cause HDFN, and detect antigens for the ABO blood group?
A
IgA causes HDFN, IgD detects ABO-related antigens
B
IgE causes HDFN, IgM detects ABO-related antigens
C
IgD causes HDFN, IgE detects ABO-related antigens
D
IgG causes HDFN, IgM detects ABO-related antigens
E
IgA causes HDFN, IgE detects ABO-related antigens
Question 2 Explanation: 
IgM molecules are too large to cross the placenta. IgA is found on mucosal membranes, and particularly the gut, so wouldn't be found in the blood. IgE (and to a lesser extent possibly IgD) is involved in hypersensitivity/allergic reactions - it doesn't mark cells out for destruction.
Question 3
Which one of the following contributes to immunological memory?
A
PAMPs
B
Antibodies
C
Neutrophils
D
Complement
E
Interferons
Question 3 Explanation: 
Antibodies are produced by the adaptive immune system and are used to detect antigens that the host organism has been exposed to. Although PAMPs (pathogen associated molecular patterns) do serve as antigens, they are recognised by parts of the innate immune system and therefore not associated with immunological memory.
Question 4
A ten year old girl presents with tonsillitis. Which type of immune tissue has been affected?
A
BALT
B
GALT
C
MALT
D
SALT
E
Thymus
Question 4 Explanation: 
MALT = mucous-associated lymphoid tissue. MALT is found in other parts of the respiratory and GI tract. Gut-specific MALT is also known as GALT (gut-associated lymphoid tissue). Peyer's patches are an example of a GALT. BALT is bronchus-associated lymphoid tissue, which is also a subset of MALT. SALT refers to skin-associated lymphoid tissue
Question 5
Which cell types form the mononuclear phagocytic system?
A
Neutrophils and macrophages and monocytes
B
Macrophages and monocytes
C
B cells and neutrophils
D
Lymphocytes, monocytes and neutrophils
E
Lymphocytes and neutrophils
Question 5 Explanation: 
Although all of the above cell types (apart from T lymphocytes) phagocytose, only macrophages and monocytes form part of the mononuclear phagocytic system.
Question 6
What is the main difference between macrophages and neutrophils?
A
Neutrophils are only found in blood, macrophages are only found in tissue
Hint:
Close - but neutrophils can also be recruited into tissue
B
Neutrophils are produced in bone marrow, macrophages are produced in lymph nodes
C
Neutrophils have multilobed nuclei, macrophages have large, rounder nuclei
D
Neutrophils phagocytose opsonised bacteria, macrophages do not
E
Neutrophils secrete cytokines, macrophages do not
Question 6 Explanation: 
Macrophages are only found in tissue where they differentiate from monocytes to tissue-specific phagocytes. While neutrophils are mainly found in blood, they can be recruited into tissue.

Both neutrophils and monocytes (the precursor to macrophages) originate in the bone marrow. Both also secrete cytokines and have the ability to phagocytose opsonised bacteria - opsonisation in the process by which molecules including antibodies and complement bind to foreign cells to increase their phagocytosis.

Question 7
True/false: fragments of viruses and cellular enzymes can both be presented by MHC class I molecules for recognition by cytotoxic T cells?
A
True
B
False
Question 7 Explanation: 
MHC class I molecules present random cellular contents to cytotoxic T cells. If a virus has infected a cell, there is a chance that proteins that make up the virus will get presented in this way. Cytotoxic T cells will detect if a cell has non-self antigens and then trigger an immune response if detected
Question 8
MHC class I molecules are expressed on all cells except:
A
Red blood cells
B
T cells
C
B cells
D
Neutrophils
E
Neurons
Question 9
You are treating a 26 year old female with a suspected viral STI. Which cytokine is most likely to be present in neighbouring, uninfected cervical cells?
A
IL-2
B
Interferon-gamma
C
Interferon-alpha
D
TNF-alpha
E
IL-6
Question 9 Explanation: 
There are two types of interferons produced during a viral infection. Type I interferons (alpha and beta) inhibit viral replication in neighbouring cells so you would see this more in neighbouring cells. Type II interferons (gamma) are involved in activating the immune response, as are the other cytokines listed.
Question 10
Which of the following is not true of B cells?
A
They are activated by T helper cells
B
They produce antibodies
C
They have receptors for IL-4
D
Proliferate on activation producing identical copies of themselves
E
They phagocytose antigens bound to cell surface antibodies
Question 10 Explanation: 
After activation, B cells undergo a series of cell divisions where the DNA for the antibody undergoes changes to increase its avidity for the antigen - a process called clonal selection. This process is believed to be a cause of auto-immunity, whereby some of the clones produce antibodies that start to detect self-antigens.
Question 11
Which antibody is mainly involved in the primary adaptive immune response?
A
IgA
B
IgD
C
IgE
D
IgG
E
IgM
Question 12
Which of the following cytokines is directly responsible for causing fever during an immune response?
A
IL-2
B
IL-4
C
IL-5
D
IL-6
E
IL-10
Question 12 Explanation: 
IL-1 and TNF-alpha also cause fever (source: 'Instant Notes Immunology' by Lydyard, Whelan and Fanger; 'The Immune System' by Peter Parham)
Question 13
In the complement cascade, which is the first complement to bind to an invading cell?
A
C1
B
C2a
C
C3b
D
C4b
E
C5b
Question 13 Explanation: 
C1 binds to antibodies

C2a and C4b combine to produce C3 convertase

C5b is produced by C3b and goes on to bind to the infected cell as well. Some sources say that C4b can also opsonise a targeted cell; however, that requires activation of C4 by C1 binding to an antibody whereas C3 can be activated by PAMPs and C reactive protein as well so is more likely to be the first molecule to bind.

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There are 13 questions to complete.

Now you’ve given the MCQs a go, try out these SAQs as well!

Which five molecules make up the membrane attack complex in the complement cascade?
C5b, C6, C7, C8, C9
What are the two main structural elements to an immunoglobulin? Which one depending on the immunoglobulin type?
Each immunoglobulin molecule consists of two heavy chains and two light chains. The nature of the heavy chains determines whether the molecule is IgA, IgD, IgE, IgG or IgM. There are also two types of light chain (kappa and lambda) but they don’t change the classification of the immunoglobulin type.
Describe three differences between the primary and secondary adaptive immune responses.
Primary immune response is slower, predominantly involves IgM and the antibodies tend to be less specific for an antigen.

The secondary immune response is faster and bigger, involves IgG, and the antibodies are more specific to the antigen.

What is opsonisation?
The binding of molecules such as antibodies and complement to a microbe which enhances its rate of phagocytosis.
Describe four differences between the innate and adaptive immune response.

Immediate vs, delayed response

Only some threats recognised vs. all threats able to be recognised

No selection of antibodies vs. clonal selection of antibodies

No memory vs. immunological memory (e.g. via B cells)

No antigen presentation vs. antigen presentation

Give four examples of barrier immunity

Barrier immunity can be split into physical and biochemical components and includes:

  • Skin
  • Mucous
  • Respiratory cilia
  • Commensal organisms
  • Gut acid
  • Enzymes (e.g. lysozyme in tears)

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