The Immune System Flashcards

1
Q

What is a hypersensitivity reaction? What are the classes of hypersensitivity response?

A

A tissue damaging immune response, which may be directed against self-antigens (autoimmunity) or harmless external antigens (allergy). There are 4 types of hypersensitivity reaction:

  • Type 1 - IgE mediated (minutes)
  • Type II - IgG / IgM mediated (hours)
  • Type III - Immune complex deposition (hours)
  • Type IV - Delatyed type hypersensitivity - T cell mediated (days / weeks)
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2
Q

What is atopy? What is the classic triad of atopic diseases?

A

Atopy is the inherited tendency to make large amounts of IgE in response to harmless external stimuli (i.e. patients are ‘hyperallergic’, presenting with regular type I hypersensitivity reactions). The classic atopic triad is:

  • Eczema (atopic dermatitis)
  • Allergic rhinitis
  • Allergic asthma
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3
Q

What is allergy? What type of hypersensitivity reactions typically occur in allergic responses, and what are the risk factors for allergic disease?

A

Allergy is a tissue damaging response to an innocuous external stimulus. It is usually type I (IgE mediated) or type IV (T-cell mediated, delayed type hypersensitivity). Risk factors include:

  • Atopy
  • Age - commoner in children in adults
  • Gender - commoner in boys than girls
  • Family size - less common in large families
  • Reduced microbial burden
  • Smoking
  • High levels of antigen exposure
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4
Q

What is anaphylaxis? What are the key clinical features?

A

Sudden, generalized cardiovascular collapse or bronchospasm, occurring when a patient reacts to a substance to which they are exquisitely sensitive. Clinical features tend to be of a more rapid onset when the antigen is introduced systemically (i.e. wasp sting) rather than absorbed (i.e. latex). Key clinical features:

  • Cardiovascular - Cardiovascular collapse
  • Respiratory - Bronchospasm / Laryngeal oedema
  • Skin - Angioedema / Urticaria
  • Gastrointestinal - Vomiting / Diarrhoea
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5
Q

What is an anaphylactoid reaction? How is it different from anaphylaxis?

A

Anaphyloid reactions produce a clinically similar result (circulatory collapse, angioedema etc), but are not mediated by IgE. They are caused by substances that induce degranulation of mast cells by direct activation or the alternative pathyway of complement activation (C3a, C5a)

The individual does not have to have been previously sensitized to the allergen

Agents include contrast medium, opioids and hot temperatures

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6
Q

What is allergic rhinitis? What are common causes of allergic rhinitis

A

An allergic inflammation of the nasal airway, causing mucosal oedema, itching and sneezing. Causes may be:

Seasonal

  • Tree pollen (late March - mid-May)
  • Grass pollen (mid-May - July)
  • Weed pollen (end of June - September)

Perennial

  • House dust mite
  • Cat
  • Dog
  • Occupational antigens
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7
Q

What is asthma, and what are the presenting features of an asthmatic attack?

A

Asthma is a syndrome characterized by three cardinal features of:

  • Generalized but reversible airways obstruction
  • Bronchial hyper-responsiveness
  • Airway inflammation

Presenting features are:

  • Chest tightness
  • Shortness of breath
  • Wheeze
  • Decreased peak flow measurement
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8
Q

Asthma may be defined as either extrinsic (atopic) or intrinsic (non-atopic). What are some important extrinsic and intrinsic factors?

A

Extrinsic:

  • Pollens
  • House dust mites
  • Occupational allergens

Intrinsic

  • Airway cooling - exercise / air temperature
  • Emotional stress
  • Irritants - smoking, fumes etc
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9
Q

What is Urticaria? What is the underlying cause?

A

Urticaria refers to transient episodes of demarcated, odematous, erythematous, pruritic lesions with a raised edge. It results from sudden fluid accumulation within the dermis due to increased local vascular permeability.

It may be acute, often caused by an IgE mediated reaction to an extrinsic antigen (as in food allergy). Chronic urticaria may also occur, which occurs often daily over a period of weeks.

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10
Q

What is angioedema?

A

Rapid swelling of the dermis and subcutaneous tissue. It is extremely similar to urticaria, except urticaria occurs in the upper dermis. Comonly occurs in allergic and anaphylactic reactions.

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11
Q

What is eczema (atopic dermatitis)? Which parts of the body does it commonly affect?

A

A common, chronic, severely pruritic, eczematous skin disease, usually occurring in individuals with a hereditary disposition to all atopic disorders, and frequently in association with high serum IgE levels.

In infants, the dermatitis often appears on the face first, followed by the flexural aspects of the arms and legs (back of knee, front of elbow).

Spontaneous resolution occurs in many patients: half clear by the age of 7, 90% by teens. However, for some it persists into adult life

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12
Q

What is the management of atopic eczema?

A

Management directed at a reduction of cutaneous inflammation (e.g. emollients) and elimination of exacerbating factors including allergens, infection and irritants.

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13
Q

What is allergic contact dermatitis?

A

An inflammatory skin disease caused by Th1-cell-mediated (Type IV) hypersensitivity to external agents which come into contact with the skin. It is considered an archetypal T-cell mediated hypersensitivity, and therefore requires 48h to develop, a characteristic of cell-mediated but not antibody mediated hypersensitivity.

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14
Q

What is the classic history of allergic contact dermatitis?

A

Typical history is biphasic - there is an induction phase from the time of initial antigen contact to sensitization of T lymphocytes, and an elicitations phase, from antigen re-exposure to the apperance of dermatitis.

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15
Q

What is autoimmune thrombocytopenic purpura? What are the primary and secondary causes?

A
  • An autoimmune condition characterised by IgG antibody to platelet antigens, leading to platelet destruction in the spleen.
  • Often occurs idiopathically, however may be secondary to:
  • SLE
  • Infection
  • Drug
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16
Q

What is the clinical presentation of autoimmune thrombocytopenia purpura? Who is most commonly affected?

A

Clinical presentation:

  • Purpura / petechiae
  • Increased bleeding e.g. epistaxis, menorrhagia
  • Bleeding from gums whilst brushing teeth

Epidemiology

  • Occurs in both children and adults. Most children will enter remission within 6 months, whereas adults are more likely to have chronic disease
  • Affects women more commonly than men (2:1)
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17
Q

On what basis is the diagnosis of autoimmune thrombocytopenic purpura made? How is the condition managed?

A

Diagnosis of exclusion, ensuring that there are no secondary causes (SLE, HIV etc). Sustained low platelet count will be the predominant result of investigation.

Antibodies will be targeted against GpIIb/IIIa on the platelet surface.

First line of treatment is with steroids to reduce the autoimmunity.

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18
Q

What is pernicious anaemia? What is the underlying pathology?

A

A megaloblastic anaemia caused by the loss of gastric parietal cells. Anaemia results from reduced B12 uptake, as parietal cells secrete intrinsic factor required for B12 uptake in the ileum.

Disease is mediated by autoantibodies targeted against either gastric parietal cells themselves, or against intrinsic factor

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19
Q

What is autoimmune thyrotoxicosis (Grave’s disease)? What is the epidemiology, and what is the underlying cause?

A
  • An autoimmune condition causing an overactive thyroid gland.
  • It occurs much more frequently in women than in men, frequently presenting during adolescence or pregnancy. It has a powerful hereditary component.
  • Underlying pathology is auto-antibodies targeted at the TSH receptor
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20
Q

What is Hashimoto’s thyroiditis? What is the most commonly used test for Hashimoto’s disease?

A
  • An autoimmune condition in which the thryoid gland is attacked by a variety of cell mediated and antibody mediated responses. It produces clinical symptoms of hypothyroidism
  • Antibodies to thyroid peroxidase (TPO) are present in virtually all patients, though they do not cause the disease and are not specific for it
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21
Q

What is type I diabetes mellitus? What is the underlying pathology and which autoantibodies may be detected during the course of the disease?

A

Destruction of beta-cells of the pancreas, mediated by auto-reactive cytotoxic T cells, leading to reduced insulin production and diabetes.

Antibodies to islet cells are present in early disease, and GAD (glutamic acid decarboxylase) are present in later disease. Note that the antibodies present are not responsible for the clinical course of the disease.

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22
Q

What is myasthenia gravis? What is the underlying pathology?

A

An autoimmune neuromuscular condition leading to fluctuating muscle weakness and fatigueability (muscles become weaker during periods of activity, and recover during rest). Most commonly presents in small muscles first, before symptoms are seen in larger muscles.

Caused by auto-antibodies targeted against acetylcholine receptors on the post-synaptic membrane of neuromuscular junctions

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23
Q

What other conditions is myasthenia gravis associated with?

A
  • Thyroid disease, including Hashimoto’s thyroiditis and Graves disease
  • Insulin dependent diabetes
  • Rheumatoid arthritis
  • Lupus
  • Demyelinating CNS diseases
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24
Q

What is pemphigus vulgaris? What is the underlying pathology?

A

A chronic blistering skin condition producing painful, flaccid blisters which are prone to scarring. It is due to disruption of the epidermal layers, and thus blisters are superficial and prone to rupture. They occur on both epidermal and mucosal surfaces

Due to autoantibodies targeted against desmosomes (desmoglein 1 and 3), disrupting the connections between squamous cells of the epidermis

25
Q

What is bullous pemphigoid? What is the underlying pathology?

A

An acute or chronic autoimmune condition defined by tense, well defined blisters on an erythematous background. They are distributed on legs and arms, but not on mucosal surfaces. It is due to subepidermal disruption, and thus blisters are more tense and less prone to rupture.

Underlying pathology of is antibodies targeted against the skin basement membrane

26
Q

What is Goodpasture’s syndrome? What is the underlying pathology?

A

An autoimmune disease in which there is attack on lungs and kidneys, leading to bleeding from the lungs and kidney failure. A typical presentation is with a burning sensation whilst urinating, followed by haematuria and haemoptysis

The underlying pathology is an antibody mediated attack on the glomerular basement membrane

27
Q

What is coeliac disease? Which auto-antibodies will be found in the serum of sufferers?

A

An autoimmune disorder of the small intestine, caused by a reaction to gliadin, found in gluten. Upon exposure to gliadin, the enzyme tissue transglutaminase (TTG) modifies the protein, causing an immune reaction against the small bowel. This leads to symptoms of steatorrhoea, weightoss and failure to thrive in children.

The key serum findings are antibodies agains tissue-transglutaminase (TTG) and endomysium. Both are IgA subtypes.

28
Q

What is autoimmune hepatitis? What is the underlying pathology?

A

Autoimmune hepatitis is acute inflammation of the liver due the antibody mediated attack of hepatocytes. It may be accompanied by dark urine, pale stools, abdominal distention and itching.

It may be associated with antibodies targeted at smooth muscle (SMA) or liver-kidney microsomes (LKM)

29
Q

What is primary biliary cirrhosis? What is the underlying pathology?

A

Irritation and swelling of the bile ducts of the liver, blocking the flow of bile. This results in liver damage and scarring leading to cirrhosis.

The diagnostic blood test for primary biliary cirrhosis is the presence of anti-mitochondrial antibodies in the blood (AMA)

30
Q

What is systemic lupus erythematosus (SLE)? Who is commonly affected, and what aetiology?

A
  • A multisystem disorder of unknown cause, it has a relapsing and remitting course.
  • It is much more common in women, particularly in women of childbearing age, with a higher incidence in afro-carribean populations
  • It is associated with autoandibodies to a number of different antigens, notably antinuclear antibody (ANA - present in almost all cases of SLE, but not specific), dsDNA (higher sensitivity and specificity) and Sm (low sensitivity, high specificity)
31
Q

Describe the common clinical presentation of SLE.

A

Has a diverse and variable presentation due to the potential multisystem pathology. Usual first presentation is with:

  • Arthritis / arthralgia
  • Skin rash - erythematous, raised, scaly, distributed across cheeks & nose in sun exposed areas. More common in summer due to UV exposure
  • Fever / mailse
  • Neuro-psychiatric problems
  • Anaemia - commonly causes a haemolytic anaemia
32
Q

Some of the autoantibodies produced in lupus are able to form immune complexes which are depositied in tissues with a rich capilliary network. Which organs may be affected in this way?

A
  • Joints
  • Kidneys
  • Brain
  • Skin
33
Q

What investigations should be performed in suspected SLE? What would the results be?

A
  • ESR / CRP - usually the ESR is raised more than the CRP unless there is a coexisting underlying infection
  • FBC / tests for renal function
  • Tests for antibodies - ANA, dsDNA, Sm
  • Biopsy of skin / kidney, examine for deposition of immune complexes
34
Q

What is Sjorgen’s syndrome? Who is commonly affected, and what is the aetiology?

A

A systemic autoimmune disease, in which immune cells attack and destroy exocrine glands, particularly those that produce tears and saliva.

Occurs much more commonly in women than men, and more frequently after the menopause. It may exist as both a primary or secondary disorder, in conjunction with rheumatoid artheritis, SLE, primary billiary cirrhosis, scleroderma etc.

The pathogenesis is not well understood. Although it is thought that viral infection may contribute.

35
Q

What are the clinical features of Sjorgen’s syndrome?

A

Hallmark symptoms of Sjorgen’s are of a ‘generalized dryness,’ particularly involving the eyes and mouth. In 60% of pathients there will also be rheumatoid arthritis.

36
Q

What investigations would be performed in Sjorgen’s syndrome, and what would the results be?

A
  • Schirmer’s test - paper strips inserted into the eye for several minutes to measure production of ears
  • Autoantibodies:
    • Anti-nuclear antibody (ANA)
    • Ro and La
  • Biopsy - minor salivary gland
37
Q

What is polymyositis? What antibodies aid in diagnosis and what other investigtions should be performed?

A

A chronic inflammation of muscles causing pain and marked weakness and loss of muscle mass, particularly in the proximal musculature including the shoulder and pelvic girdle.

Antibodies aiding in diagnosis are anti-nuclear antibody and Jo-1. These are also used in the diagnosis of dermatomyositis

Other findings include a raised creatine kinase and muscle biopsy demonstrating T cell mediated damage.

38
Q

What is dermatomyositis? How does it differ from polymyositis, and what antibody investigations would be performed?

A

Dermatomyositis is a connective tissue disease related to polymyositis, characterized by inflammation of muscles and skin. It is defined as polymyositis PLUS a scaly rash on sunlight exposed areas (similar to the rash of SLE)

Like polymyositis, it is associated with ANA and Jo-1. It is important to also test for dsDNA or Sm to rule out SLE.

39
Q

What is Scleroderma? What are the two forms?

A

A chronic, systemic autoimmune disease, characterized by fibrosis, vascular alterations and autoantibodies. There are two forms:

Limited systemic scleroderma:

  • Cutaneous manifestations mainly affecting hands, arms and face
  • Previously called CREST syndrome - Calcinosis, Raynaud’s phenomenon, Esophagel dysfunction, Sclerodactyly, Telangiectasis

Diffuse systemic scleroderma

  • Rapidly progressing and affects a large area of the skin and one or more internal organs, frequently the kidneys, oesophagus, heart and lungs.
40
Q

Describe the clinical presentation of scleroderma.

A
  • Scleroderma is characterized by the appearance of circumscribed or diffuse, hard, smooth, ivory colored areas that are immobile and give the appearance of hidebound skin.
  • Typical scleroderma is classically defined as symmetrical skin thickening, with 90% also presenting with Raynaud’s phenomenon and nail-fold capilliary changes.
41
Q

Which antibodies may be expected to be present in:

  1. Limited scleroderma
  2. Diffuse scleroderma
A

Limited scleroderma:

  • Antinuclear antibodies (ANA)
  • Anticentromere antibodies

Diffuse scleroderma

  • Antinuclear antibodies (ANA)
  • Scl-70 antibodies
42
Q

Which autoantibodies are typically present in seum in patients suffering from systemic vasculitis?

A
  • Anti-neutrophil cytoplasmic antibody (ANCA)
43
Q

Which autoantibodies are typically found in patients suffering from rheumatoid arthritis?

A
  • Rheumatoid factor
44
Q

Review the functions of the different classes of immunoglobulins

A
  • IgA - agglutination of bacteria, active transport into secretions
  • IgE - interaction with mast cells and basophils
  • IgG - Complement activation, opsonisation, neutralisation, transport across placenta
  • IgM - agglutination, complement activation
45
Q

What is X-linked antibody deficiency (Bruton’s agammaglobinaemia)? What is the underlying genetic abnormality, and how is it carried?

A
  • An X linked genetic disorder in which the inability to generate mature B cells manifests as a complete lack of antibodies in the blood stream. Patients are prone to developing serious and often fatal infections
  • Due to defective B-tyrosine kinase, required for maturation of B cells. Mothers carry gene, sons are affected. Daughters may be carriers
46
Q

What is the presentation of Brutons? How is diagnosis made? What is the treatment?

A
  • Patients present in early childhood with recurrent infections, particularly with encapsulated bacteria.
  • Diagnosis made based upon the history of recurrent infections, and blood tests showing a lack of circulating B cells and low levels of all antibody classes.
  • Treatment by infusion of IvIg every 3-4 weeks throughout life
47
Q

What is common variable immunodeficiency? Who does it present in and how will the antibody deficiency manifest?

A

A group of 150 immunodeficiencies which have a common set of features but different underlying causes.

It is the most commonly encountered immunodeficiency which usually presents in childhood but can be seen in later life

Antibody deficiency manifests as variable but usually low levels of IgG (most commonly), IgA or IgM. It is a diagnosis of exclusion. May also be allergy, autoimunity, and malignancy.

48
Q

What is selective IgA deficiency? How is it often identified?

A

A relatively mild genetic immunodeficiency in which individuals lack IgA, but have normal serum IgG and IgM. As IgA lines the mucous membranes of the mouth, airways and digestive tract, there is an increased tendancy for respiratory, digestive and genitourinary infections

It may have a similar presentation to CVID, however, it does not present with the same lymphocyte subpopulation abnormalities.

Often an incidental finding which investigation for coeliac disease

49
Q

What conditions are individuals with selective IgA deficiency at increased risk of developing?

A
  • Allergy
  • Autoimmunity
  • Malignancy
  • Transfusion reactions
50
Q

What is severe combined immunodeficiency?

A

A genetic disorder associated with impairment of both B and T cells, resulting in severe immunodeficiency and chronic diarrhoea, ear infections, recurrent pneumocystis jirovecii pneumonia, and profuse oral candidiasis.

There are multiple genetic abnormalities which lead to SCID including X-linked SCID (IL-2 receptor abnormality), Omenn syndrome (RAG-1 and RAG-2 deficiency) and Bare lymphocyte syndrome (no MHC II expression)

51
Q

Which clues point towards a SCID?

A
  • Presentation in first weeks / months of life
  • Infections are often viral or fungal rather than bacterial
  • Chronic diarrhoea is common, and often labelled as ‘gastro-enteritis’
  • Respiratory infections and oral thrush are common
  • Failure to thrive in absence of obvious infections
  • Lymphopenia is present in almost all affected infants
52
Q

What is CD40L deficiency? How does it most commonly present?

A
  • Hyper IgM syndrome, in which serum IgM are raised but other immunogloblin types are low due to a failure of class switching.
  • Commonly presents with pneumocystis pneumonia infection in infants.
  • Infections are recurrent, due to the inability to form lasting immunity via plasma cells
53
Q

What is Di George syndrome?

A

22q11.2 deletion causing thymic hypoplasia and resulting immune deficiency. Clinical signs can be remembered by ‘CATCH 22’:

  • Cardiac abnormalities
  • Abnormal facies
  • Thymic aplasia
  • Cleft palate
  • Hypocalcaemia / Hypoparathryoidism (leading to neonatal tetany)

Severe T cell deficiency and recurrent infections are rare.

54
Q

What is chronic mucocutaneous candidiasis?

A

An immune disorder of T cells characterized by chronic infections with Candida that are limited to mucosal surfaces, skin and nails.

Has endocrine associations including hypoparathyroidism, addison’s disease and thyroid disorders

55
Q

What is C1 inhibitor deficiency? How does it present, and how is it distinguised from other forms of angioedema?

A

C1 inhibitor is the main controller of bradykinin production, as well as inhibiting the activation of C1 in the classical pathway.

Deficienct leads to recurrent angioedema at any location, including the throat, which is potentially fatal. It is differentiated from other forms of angioedema by:

  • Duration of swelling (days)
  • Bowel wall angioedema with distension, severe pain, vomiting, diarrhoea
  • Characteristic rash (similar to erythema marginatum - NOT urticarial)
  • Family history (autosomal dominant)
56
Q

How is a diagnosis of C1 inhibitor deficiency made? What are the principles of management?

A

Diagnosis:

  • Measurement of complement C4 (low) and C3 (normal) as initial screen
  • Measure C1 inhibitor concentration and function (15% of patients have normal concentration but reduced function of C1 inhibitor)

Management

  • Acute swelling - C1 inhibitor concentrate
  • Prevent swelling - aoid triggers
  • Education, support, genetic counselling etc.
57
Q

What is chronic granulomatous disease?

A

An X linked or autosomal recessive condition in which there is impaired killing of coagulase-positive microorganisms by neutrophils due to a defect in respiratoy burst enzymes.

Patients present with deep seated abscesses / infection due to Staphylococcus aureus and aspergillus plus granuloma formation mimicking sarcoidosis or Chron’s disease

58
Q

How is the diagnosis of chronic granulomatous disease made? What is the treatment?

A

Diagnosis:

  • Nitroblue tetrazolium reductase test (microscopy)
  • Dihydrorhodamine reductase test (flow cytometry)

Treatment:

Antibiotics and antifungal prophylaxis and acute treatment as required. Stem cell transplant may be curative.