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MRCEM Pathology > Immune responses > Flashcards

Immune responses Flashcards

1
Q

Anti-A and Anti-B are naturally occurring antibodies. What type of immunoglobulins are they usually?

A

IgM

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2
Q

The most important immune antibody is the Rh antibody, anti-D. What type of immunoglobulin are they commonly?

A

IgG, though some IgM may also develop in the early phase of an immune response.

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3
Q

What type of immunoglobulin is the only one capable of transplacental passage?

A

IgG

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4
Q

Which is more common, RhD-ve or RhD+ve?

A

RhD+ve (about 85% of the UK population)

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5
Q

Immunoglobulins are composed of two identical heavy and two identical light chains linked by what?

A

Disulphide bridges

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6
Q

Which immunoglobulin is most abundant in plasma and the pain circulatory Ig for the secondary immune response?

A

IgG

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7
Q

Which immunoglobulin is the main Ig in the primary immune response and the most proficient at complement fixation?

A

IgM

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8
Q

Which immunoglobulin is the major Ig in secretions, particularly from the GI tract (but also in saliva, tears, sweat and breast milk)?

A

IgA

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9
Q

Which immunoglobulin is important for mast cell degeneration in allergic and anti parasitic response?

A

IgE

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10
Q

Which immunoglobulin is expressed on naive B-cells and its function is not known?

A

IgD

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11
Q

Name some functions of antibodies?

A
  1. Neutralise toxins and prevent attachment of pathogens
  2. Target, opsonise or agglutinate antigens for phagocytosis
  3. Activate the complement cascade
  4. Act as antigen receptors on B lymphocytes
  5. Activate antibody-dependent cell-mediated cytotoxicity by natural killer (NK) cells or T cytotoxic cells
  6. Provide mucosal immunity
  7. Stimulate degranulation of mast cells
  8. Provide passive immunity to the newborn
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12
Q

True or false: Inflammatory mediators cause:
1. Vasoconstriction
2. Increase endothelial permeability

A
  1. False, inflammatory mediators cause vasodilation (heat and redness)
  2. True, and therefore oedema occurs
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13
Q

Injured, infected or cancerous cells express pathogen-associated molecular patterns (PAMP)-like molecules which are recognised by what kind of cells, which kill the cells?

A

Natural killer cells

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14
Q

How long does the adaptive immune response take to become effective and peaks after how long?

A

5 days to become effective.
Peaks after 1-2 weeks.

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15
Q

Cell-mediated immunity is directed towards antigen within cells, which are made visible by what complex, and which cells proliferate on recognising the antigen and destroying the infected cell?

A

Class I major histocompatibility complex (MHC I). MHC I is found on the surface of cells and displays antigen to cytotoxic T cells.

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16
Q

Humoral immunity is particularly effective against extracellular pathogens, as it involves secretion of antibodies into extracellular fluid. When an antigen binds to its matching receptor on naive B-cells, the latter activates and undergoes what?

A

Clonal expansion - naive B cells differentiate into plasma cells which secrete antibody in massive amounts. T helper cells enhance the response if the antigen is a protein. Memory cells which persist for years are also produced during clonal expansion.

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17
Q

In humoral immunity, T helper cells only recognise protein antigens when they are presented to them by which complex on antigen presenting cells (APCs)?

A

Class II major histocompatibility complex (MHC II)

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18
Q

In the spleen, the membrane flexibility of aged and abnormal red cells is impaired, and they are trapped within the sinus where they are ingested by what?

A

Macrophages

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19
Q

The spleen is not a site of erythropoiesis in the normal adult, but this may be re-established in both the liver and spleens extra medullary haemopoiesis in which disorders?

A

Myelofibrosis, chronic severe haemolytic and megaloblastic anaemia

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20
Q

Name some causes of splenomegaly?

A

Infectious mononucleosis
Haematological malignancy
Portal hypertension
Malaria
Schistosomiasis
Chronic myeloid leukaemia (CML)
Primary myelofibrosis
Leishmaniasis

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21
Q

Normally, what percentage of the total red cell mass, the total marginating neutrophil pool and the total platelets are present in the spleen?

A

5% of the total red cell mass
Up to 50% of neutrophils
30% of platelets

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22
Q

In hypersplenism, what proportion of the total red cells and platelets may be pooled in an enlarged spleen?

A

40% of the red cell mass
90% of platelets

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23
Q

Functional hyposplenism is characterised by what on blood film?

A

Howell-Jolly bodies (or siderotic granules on iron staining)

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24
Q

Name some causes of hyposplenism?

A

Surgical removal
Sickle cell anaemia
Gluten-induced enteropathy
Amyloidosis

25
Q

Patients with hyposplenism are at lifelong risk of infection. The most characteristic susceptibility is to what 3 bacteria?

A

Streptococcus pneumonia
Haemophilus influenza type B
Neisseria meningitidis

26
Q

Granulocytes (neutrophils, eosinophils, basophils) spend only 6-10 hours in the circulation before entering tissues. They spend 4-5 days in the tissues before they are destroyed during defensive action or as the result of what?

A

Senescence

27
Q

What is the lifespan of neutrophils in the blood?

A

6-10 hours

28
Q

Neutrophils contain granules which are divided into primary and secondary. What is the difference between the 2 types of granule?

A

Primary - appears at the promyelocyte stage, contains myeloperoxidase and other acid hydrolases.
Secondary - appears at the myelocyte stage and predominate in the mature nucleus, contains lactoferrin, lysozyme and other enzymes.

29
Q

Eosinophils comprise of what percentage of circulating white cells?

A

1-3%

30
Q

What is the largest type of granulocyte?

A

Basophil

31
Q

Basophils have many dark cytoplasmic granules which overlie the nucleus and contain what?

A

Heparin and histamine

32
Q

Mast cells have granules containing preformed mediators such as what?

A

Tryptase
Histamine
Serotonin
Heparin

33
Q

Mast cells can secrete newly formed mediators such as what?

A

Prostaglandin D2
Bradykinin
Cytokines
Leukotrienes

34
Q

What triggers mast cell degranulation?

A

Cross-linking high affinity receptors for the Fc portion of IgE

35
Q

What does mast cell degranulation result in?

A

Increased capillary permeability.
Vasodilation.
Smooth muscle contraction.
Platelet aggregation and activation.
Complement activation.
Increased mucus secretion.
Chemotaxis of leukocytes.

36
Q

Monocytes spend only a short time in the marrow and, after circulating for 20-40 hours, leave the blood to enter the tissues where they become what?

A

Macrophages

37
Q

What is the lifespan of macrophages?

A

As long as several months or even years

38
Q

In tissues macrophages become self-replicating without replenishment from the blood. They form specific functions in different tissues, give some examples?

A

Kupffer cells in the liver.
Alveolar macrophages in the lung.
Intraglomerular mesangial cells in the kidneys.
Microglial cells in the brain.
Langerhans cells in the skin.
Histocytes in connective tissue.

39
Q

Name ways macrophages may be activated?

A

Cytokines, such as IFN-gamma.
Contact with complement.
Direct contact with the target cell through leucocyte adhesion molecules.

40
Q

In phagocytosis by monocytes and neutrophils, recognition of a foreign particle is aided by opsonisation with immunoglobulin or complement because both neutrophils and monocytes have what receptors?

A

Fc and C3b receptors

41
Q

Are helper T cells CD4+ or CD8+ T cells?

A

CD4+ T cells (CD8+ T cells are cytotoxic T cells)

42
Q

Do CD4+ T cells (helper T cells) recognise antigens only in association with HLA class I or II?

A

HLA class II (CD8+ T cells recognise antigen only in association with HLA class I)

43
Q

In the complement cascade what is the most abundant and pivotal protein?

A

C3

44
Q

In opsonisation the early stages leading to coating of cells with C3b can occur but which 2 pathways?

A
  1. The classical pathway usually activated by IgG or IgM coating of cells.
  2. The alternative pathway which is more rapid and activated by IgA, endotoxin and other factors.
45
Q

C3 deficiency leads to increased susceptibility of infection with encapsulated organisms. Name 2 of these organisms?

A

S. pneumoniae and H. influenza

46
Q

If the complement sequence goes to completion, there is generation of what?

A

An active phospholipase (the membrane attack complex -MAC) that punches holes in the cell membrane causing cell lysis.

47
Q

C5-C9 deficiency results in increased susceptibility to what family bacterial and why?

A

Neisseria family, because the MAC (membrane attack complex) appears to be the only way of killing the Neisseria family.

48
Q

The complement pathway generates the biologically active fragments C3a and C5a which are chemoattractant for neutrophils and monocytes and stimulate degranulation of which blood cells?

A

Mast cells and basophils

49
Q

The complement pathway is regulated by complement inhibitors (e.g. decay accelerating factor or C1 inhibitor). Deficiency in C1 inhibitor results in what?

A

Hereditary angioedema

50
Q

The complement pathway is regulated by complement inhibitors (e.g. decay accelerating factor or C1 inhibitor). Deficiency in complement decay-accelerating factor results in what?

A

Paroxysmal nocturnal haemoglobinuria

51
Q

Type I (immediate) hypersensitivity is mediate by IgE with immediate degranulation of mast cells and basophils. Overproduction of IgE in response to innocuous environmental antigen occurs in allergy and atopic individuals. Give some examples?

A

Allergic rhinitis
Allergic conjunctivitis
Allergic asthma
Systemic anaphylaxis
Angioedema
Urticaria
Penicillin allergy

52
Q

Type II (antibody-mediated) hypersensitivity occurs when antibody (IgG or IgM) specific for cell surface antigens is produced. Give some examples?

A

Incompatible blood transfusions
Haemolytic disease of the newborn
Autoimmune haemolytic anaemias
Goodpasture’s syndrome
Rheumatic heart disease
Bullous pemphigoid

53
Q

The following are an example of what type of hypersensitivity: Extrinsic allergic alveolitis, SLE, post-streptococcal glomerulonephritis, reactive arthritis, rheumatoid arthritis?

A

Type III (Immune complex-mediated) hypersensitivity

54
Q

Type III hypersensitivity occurs when what type of antibody reacts to free soluble antigen by forming antibody-antigen complexes called an immune complex?

A

IgG

55
Q

Type IV (delayed T-cell-mediated) hypersensitivity is caused by activated T lymphocytes that injure cells by direct killing or releasing cytokines that activate macrophages. Give some examples?

A

Contact dermatitis
Hashimoto’s thyroiditis
Primary biliary cholangitis
Tuberculin skin test (Mantoux test)
Chronic transplant rejection
Granulomatous inflammation (e.g. sarcoidosis, Crohn’s disease)

56
Q

How long after contact with the antigen do type IV hypersensitivity reactions peak?

A

48-72 hours

57
Q

An increase in blood basophils is uncommon, name some causes?

A

Myeloproliferative disorder
Myxoedema
Chickenpox infections
Ulcerative colitis

58
Q

Name conditions which can cause lymphocytosis?

A

Viral infections
Bacterial infections
CLL
ALL
Non-Hodgkin lymphoma
Thyrotoxicosis

59
Q

Name situations when lymphopenia can occur?

A

Immunodeficiency (e.g. HIV infection)
Hodgkin lymphoma
Widespread irradiation
Severe bone marrow failure
Corticosteroid and other immunosuppressive drug therapy

MRCEM Pathology (4 decks)

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