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Immunology Flashcards

1
Q

Describe the main features of the innate immune system.

A
  • Pre-existing defences
  • First-line defence
  • Responds to broad types of threats, rather than specific pathogens
  • No change in response with repeated exposure
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2
Q

Describe the main features of the adaptive immune system.

A
  • Recognises and responds to specific threats (specificity)
  • Mounts a highly tailored response against specific threat
  • Takes time to develop
  • stronger/faster response with repeated exposure (immunological memory)
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3
Q

List the initial defences of the innate immune system:

A
  • physical barriers
    • skin
    • mucous membranes
  • chemical barriers
    • acidic pH in GI tract and on skin
    • enzymes (lysozyme) in tears and saliva
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4
Q

Name the three phagocytic cells of the innate immune system:

A
  • neutrophils
  • monocytes
  • macrophages
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5
Q

What is the roll of neutrophils?

A
  • short lived cells
  • recruited to sites of inflammation
  • phagocytosis
  • contain numerous granules rich in degradative enzymes and anti-microbial substances
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6
Q

What are the roles of eosinophils and basophils?

A
  • defence against parasites
  • allergic inflammatory reactions
  • also contains granules rich in degradative enzymes and anti-microbial substances (they are granulocytes)
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7
Q

What are monocytes?

A
  • myeloid derived cells, leave bone marrow
  • circulate in blood
  • phagocytic
  • migrate into tissues where they differentiate
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8
Q

What are macrophages?

A
  • monocyte derived tissue-based cells (monocytes differentiate into macrophages when they move into tissues)
  • phagocytes
  • secrete cytokine
  • link to adaptive immune response as they are APCs
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9
Q

What is a dendritic cell?

A
  • widespread in various subsets
  • phagocytic –> type of APC (link to adaptive immune system)
  • also ingests extracellular fluid to find non-self antigens and present them to the adaptive immune system
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10
Q

what is a natural killer cell?

A
  • type of ‘large granular’ lymphocyte
  • kill infected cells and tumour cells (recognise lack of normal ‘self’
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11
Q

What is an epitope?

A
  • the particular part of the antigen recognised bu the innate or adaptive immune system receptor
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12
Q

What are antigen presenting cells?

A
  • APCs are cells that express the MHC class II - part of the cell that has been phagocysed is joined to the MHC class II protein and then this complex is expressed on the surface of the cell
  • the main APCs that link the adaptive to the innate immune system are:
    • dendritic cells
    • macrophages
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13
Q

What are the two arms of the adaptive immune system?

A
  • cell mediated: CD4+and CD8+ T lymphocytes
  • humoral: B lymphocytes and antibodies
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14
Q

Describe the structure of an antibody?

A
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15
Q

Describe the structure of a T cell receptor, that is found on the surface of a T cell:

A
  • each T cell expresses a TCR of a single specificity
  • TCRs recognise antigen expressed on cell surface in conjunction with MHC molcules
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16
Q

What are CD4 and CD8 co-receptors?

A
  • on the surface f T cells
  • Determine if T cells bind to MHC class I or II molecules
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17
Q

What is the role of CD4+ cells?

A
  • recognise antigen expressed on cell sirface in conjunction with MHC class II (only present on specialised APCs)
  • results in T cell activation under appropriate circumstances, and division to form ‘effector cells’
  • also known as helper T cells
  • after activation:
    • multiply and form multiple daughter cells that migrate to site of inflammation/infection via the bloodstream
  • produce cytokines that direct the immune response
    *
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18
Q

What is the role of CD8+ T cells?

A
  • kill infected cells (cytotoxic T cells)
  • recognise antigen expressed on the surface in conjunction with MHC class I (expressed by all cells - this is how a cell will flag itself to the immune system as being infected by e.g. a virus)
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19
Q

What is the role of a B cell?

A
  • Express B cell receptor, which is basically a membrane bound antibody
  • BCR comes into contact with antigen that matches > internalised, broken down and presented via MHC class II > binds with CD4 T helper cell > helper t cell activates B cell, causing it to produce more of the antibody and secrete it
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20
Q

What is the role of peripheral (secondary) lymphpid tissue?

A
  • where adaptive immune response are initiated
    • lymph nodes
    • spleen
    • mucosal associated lymphoid tissue (area in GI tract)
  • faciliates antigen and lymphocytes to come together, allowing adaptive immune responses
    • dendritic cells expressing antigen migrate from tissues to secondary lymphoid organs
    • naive lymphocytes circulate through lymph nodes via the blood stream
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21
Q

Give an outline of the circulation of lymph:

A
  • Lymph is essentially extracellular fluid from all tissue, but contains APCs bringing antigen from tissue
  • Drains in a series of afferent lymphatic vessels into secondary lymphoid tissues
  • Fluid (lymph) then leaves lymph nodes via efferent lymphatic vessels, which drain into a collecting lymphatic vessel called the thoracic duct
  • This then drains into the bloodstream via the heart
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22
Q

What is the purpose of the lymphatic system?

A
  1. allows peripheral fluid to drain back towards the secondary lymphoid organs
  2. brings APCs into contact with the adaptive immune system where it can be activated
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23
Q

Describe the journet of lymphocytes through the lymphatic system:

  • naïve lymphocytes enter the lymph nodes from the bloodstream
  • there they sample the environment for antigen presented by APCs
  • if they encounter their antigen and are activated, they divide to form ‘effector’ cells
  • effector lymphocytes (or naïve cells that have not encountered their antigen) leave lymph nodes via efferent lymphatics
  • drain into thoracic duct and back into bloodstream
  • activated ‘effector’ cells then home to inflamed tissues (e.g. sites of infection)
  • naïve cells home back to lymph nodes again and continue to circulate between lymph nodes and blood until antigen encountered
A
  • naïve lymphocytes enter the lymph nodes from the bloodstream
  • there they sample the environment for antigen presented by APCs
  • if they encounter their antigen and are activated, they divide to form ‘effector’ cells
  • effector lymphocytes (or naïve cells that have not encountered their antigen) leave lymph nodes via efferent lymphatics
  • drain into thoracic duct and back into bloodstream
  • activated ‘effector’ cells then home to inflamed tissues (e.g. sites of infection)
  • naïve cells home back to lymph nodes again and continue to circulate between lymph nodes and blood until antigen encountered
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24
Q

Describe active immunity and how it is acquired:

A
  • protection that is produced by an individual’s own immune system and is usually long-lasting
  • acquire by natural disease or vaccination
  • involves generation of adaptive immune responses, resulting in immunological memory
  • includes antibody responses (B cells) and cell mediated responses (T cells), usually in combination
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25
Q

Describe passive immunity and how it is acquired:

A
  • protection provided by transfer of antibodies from immune individuals
  • commonest examples if cross-placental transfer of antibodies from mother to child
  • also used therapeutically through transfusion of blood or blood products including immunoglobulins
  • gives temporary protection, only a few weeks or months
    • related to half-life of antibodies
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26
Q

List the European Society for Immunodeficiencies warning signs for ADULT primary immunodeficiency diseases:

A
  • Four or more infections requiring antibiotics within one year (otitis, bronchitis, sinusitis, pneumonia)
  • Recurring infections or infection requiring prolonged antibiotic therapy
  • Two or more severe bacterial infections (osteomyelitis, meningitis, septicaemia, cellulitis)
  • Two or more radiologically proven pneumonia within 3 years
  • Infection with unusual localization or unusual pathogen
  • PID in the family

Also remember Failure to Thrive in paediatrics

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27
Q

How do antibodies deficiencies present?

A
  • Recurrent bacterial infection
  • Main sites are chest, sinuses (i.e. respiratory tract)
  • Ear and eye infections also common
  • Recurrent infection eventually causes end organ damage e.g. bronchiectasis
  • Primarily encapsulated bacteria
    • E.g Streptococcus pneumoniae (Pneumococcus), Haemophilus, Klebsiella, Pseudomonas etc.
    • These have polysaccharide capsule that impairs phagocytosis by phagocytes (e.g. neutrophils and macrophages)
    • Antibodies are produced against polysaccharide antigens in capsule
  • Binding of antibodies results in ‘opsonisation’, greatly enhancing phagocytosis by phagocytes
  • Viruses can usually be cleared, but difficulty forming protective immunity can lead to recurrence (e.g. recurrent shingles)
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28
Q

Name possible causes of secondary antibody deficiencies:

A
  • More common than primary
  • Drugs [cytotoxics, anti-convulsants, anti-rheumatics, Rituximab]
  • Radiation
  • Malignancy [CLL, myeloma]
  • Loss [gut, kidney]
  • Nutrition [B12]
  • Metabolic
  • Infections (HIV, CMV, EBV, Toxoplasma)
  • Extremes of age / immunosenescence
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29
Q

What basic tests would you like to do to identify possible secondary cause of antibody or other problems leading to recurrent infection?

A

FBC

  • Haemoglobin & indices
    • Malabsorption, anaemia of chronic disease
    • Evidence for marrow failure
  • Thrombocytopenia
  • White cell count
    • Lymphopenia or lymphocytosis
    • Neutropenia
  • Blood film
    • Abnormal cells [smear cells, blasts]

Biochemistry

  • Liver function tests
    • Albumin for renal or GI loss
  • Thyroid function
  • Creatinine & urea [renal disease]
  • Blood glucose [HbA1c]
  • Urinary protein excretion [Stick test first]
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30
Q

Routine testing for immunoglobulins:

A
  • Routine testing involves testing IgG, IgA and IgM (together constitute almost all serum immunogobulin)
    • Normal range (adults)
      • IgG 5.8 - 15.4 g/L
      • IgA 0.64 - 2.97 g/L
      • IgM 0.24 – 1.9 g/L (male), 0.71 – 1.9 (female)
    • Age-specific ranges in children
  • Normal levels do not exclude significant immunodeficiency
  • If considering hyper-IgE syndrome also need to check total IgE [typically very raised often >50,000 kU/l]
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31
Q

Describe immunoglobulins by age:

A
32
Q

What is X-linked agammaglobinaemia?

A
  • Defect is loss of function mutation in BTK (Bruton’s tyrosine kinase)
  • This is involved in signalling of pre B cell receptor and B cell receptor
  • Absence causes block in maturation at pro-B cell stage
  • No mature B cells form
  • Classically leads to:
    • Total absence of circulating B cells
    • Absent immunoglobulins (IgG, IgA, IgM)
33
Q

How does XLA manifest?

A
  • Presents in male children (X-linked), with infections usually starting in first year of life (when maternal IgG dwindles, so not at birth)
  • Recurrent upper and lower respiratory tract infections
  • Encapsulated bacteria, e.g. Strep pneumoniae, Haemophilus influenzae, Staph aureus, Pseudomonas
  • Invariably develop bronchiectasis, especially if delayed diagnosis
  • Other bacterial infections e.g. meningitis, osteomyelitis, septic arthritis
  • Most viral infections can initially be cleared, but sensitive to enteroviruses, including polio live vaccine strain
34
Q

How do you treat XLA?

A
  • Immunoglobulin replacement (subcutaneous or intravenous) is essential life-long
  • Sometimes prophylactic antibiotics are also required
  • Goal is to prevent end organ damage particularly bronchiectasis
  • Severe refractory cases can treated curatively with haematopoietic stem cell transplant (HSCT)
  • No live vaccines
35
Q

What is common variable immunodeficiency (CVID)?

A
  • Relatively common as PIDs go, but still rare (approx. 1 in 25000)
  • Variable, as in reality it is probably many different genetic defects, with broadly similar phenotype (many identified, many likely yet to be)
  • Primarily antibody deficiency, particularly low IgG (and IgA)
  • Can present from childhood (not infancy) until well into adulthood
  • Diagnosis often delayed many years after first manifestations
36
Q

List the CVID diagnostic criteria:

A

At least one of:

  • Increased susceptibility to infection
  • Autoimmune manifestations
  • Granulomatous disease
  • Unexplained polyclonal lymphoproliferation
  • Affected family member with Ab deficiency

AND

  • Marked decreased in IgG and IgA (+/- IgM)

AND at least one of:

  • Poor vaccine response (or absent isohaemaglutinins)
  • Low class-switched memory B cells

AND

  • Secondary causes excluded

AND

  • Diagnosed after 4th year of life (although symptoms may have begun earlier)

AND

  • No evidence of a profound T cell deficiency (2 or more of):
  • CD4 numbers/microliter: 2-6y <300, 6-12y <250, >12y <200
  • % naive of CD4: 2-6y <25%, 6- 16y <20%, >16y <10%
  • T cell proliferation absent
37
Q

How does CVID manifest?

A
  • Bacterial infections, as with XLA
  • Autoimmune disease (e.g. haemolytic anaemias, cytopenias, thyroid disease and rheum arthritis)
  • Enteropathy, Coeliac-like, Malabsorption
  • Lymphoproliferation
  • Sarcoid-like granulomatous disease, can affect any organ
  • Granulomatous lymphocytic interstitial lung disease (GLILD) – serious manifestation from CVID that requires treatment with steroids
  • Liver disease (nodular regenerative hyperplasia)
  • Malignancy, especially lymphoma (40 fold increased risk)
38
Q

What is the treatment for CVID?

A
  • Immunoglobulin replacement as with XLA
  • Prophylactic antibiotics
  • Treatment of complications, e.g. autoimmune disease as appropriate
  • Some patients with active autoimmune disease or GLILD require immunosuppression, including steroids
  • Monitoring for malignancy, particularly lymphoma
  • Small (but increasing) numbers of complex patients treated with HSCT (curative but high mortality risk in adults, especially with comorbidity)
39
Q

What is specific antibody deficiency?

A
  • It is possible to have normal total antibody levels, but fail to produce antibodies to certain types of antigens (particularly polysaccharide) – esp important in encapsulated bacteria
  • This can be clinically significant, resulting in recurrent bacterial infections and risk of bronchiectasis
  • By definition IgG, IgA and IgM levels are normal
  • Specific bacterial antibodies, particularly to Strep pneumoniae (Pneumococcus) and Tetanus should be checked.
  • If low, this does not necessarily mean a problem (may not have been vaccinated or significantly exposed
  • Test vaccination given (e.g. PPV23), and levels repeated at 4-6 weeks
  • Failure to adequately respond suggests SpAD
  • Diagnostic criteria also required no evidence of T cell defect (combined immunodeficiency)
40
Q

How do you treat SpAD?

A
  • Prophylactic antibiotics in first instance
  • Immunoglobulin replacement if ongoing recurrent infection
41
Q

What is selective IgA deficiency?

A
  • Selective IgA deficiency (absent IgA, IgG and IgM normal) is common (approx. 1/800), usually incidental finding (Coeliac screening – anti-TTG is an IgA so have to check the patient is not IgA deficient before using this test) and mostly not clinically relevant
    • In absence of recurrent infection, no further investigation needed
  • Rarely it can be associated with other antibody deficiencies (e.g. specific antibody deficiency) so if recurrent infections warrants investigation
42
Q

T cell deficiency:

A
  • T cells required to clear viral and protozoal infection
  • T cells required to clear intra- and extracellular bacterial infection
  • Patients present with persistent viral infection, protozoal infection +/- bacterial infection
43
Q

What is a classic presentation of SCID?

A
  • <12 months
  • Persistent gut, resp viral infection
  • Pneumocystis
  • Maternal-foetal engraftment
  • Absent thymopoiesis (not making T cells)
    • absent or very low number of T cells
    • very low T cell function
44
Q

List infections commonly seen in combined T & B cell deficiencies:

A
  • bacterial
    • intracellular (mycobacteria)
    • Salmonella spp
  • fungal
    • Candida spp
    • Aspergillus spp
    • Cryptococcus neoformans
  • protozoal
    • Pneumocystis carinii
    • Toxoplasma gondii
    • Cryptosporidia
  • Viral
    • Respiratory: RSV, Parainfluenzae
    • GI: rotavirus (vaccine strain), norovirus
    • Other: CMV, adenovirus
45
Q

What investigations and findings would you find in SCID?

A
  • Absolute lymphocyte count <2.5x109/L
  • Lymphocyte subsets
    • decreased CD3, CD4 & CD8 (decreased CD19)
  • Lymphocyte proliferations
    • Decreased PHA
  • Igs
    • Decreased (beware ‘low normal’ if first few weeks of life as maternal IgG present – in this case check IgM)
46
Q

What is Omenn syndrome?

A
  • type of SCID
  • some T cells are produced but they are not properly activated and can be self-reactive
47
Q

What is found in Omenn syndrome?

A
  • T cell infiltration of skin, gut, liver, spleen
  • clinically GvHD - autologous T cells
  • clonal lymphocytes
    • raised T cells
    • absent B cells
    • normal NK
  • eosinophilia
  • Agammaglobulinaemia (increased IgE)
  • absent thymopoiesis
48
Q

What genetic mutation is found in Omenn syndrome?

A
  • missense mutation in Rag-1 or Rag-2
  • resulting in partial V(D)J recombination
  • other gene mutations can also contribute to Omenn syndrome
49
Q

What is the pathogenesis of Omenn syndrome?

A
  • abnormal thymic development (due to abnormal T cell production)
  • aberrant clonal T cell expansion (abnormal production of T cells in one family)
  • autoantibodies to antigen (as thymus not developed properly so cannot ‘educate’ T cells
  • mismatch in T cell/Treg repertoire
  • environmental trigger
50
Q

CD40 L or CD40 deficiency

A
  • technically a combined deficiency as deficient in T cells, but also cannot activate B cells
  • U/LRTI from infancy
  • pneumocystis jirovecii pneumonia
  • giardia lamblia or crytosporidium diarrhoea (chronic diarrhoea that can lead to ascending cholangitis and liver disease –> therefore increased risk of HCC)
  • sclerosing cholangitis associatde with crypto infection
  • neutropenia with persistent stomatitis and mouth ulcers
  • HCC
51
Q

How to diagnose CD40(L) deficiency?

A
  • raised IgM, low/absent IgA & IgG - therefore also known as hyper IgM syndrome
  • normal CD19 (normal number of B cells, but they just aren’t being activated to switch to making IgA and IgG)
  • lack of CSM B cells
  • reduced/absent CD40L expression
  • genetic confirmation
52
Q

DOCK 8 deficiency

A
  • dedicator of cytokinesis 8
  • expressed in placenta, pancreas, lungs and lymphocytes
  • important in lymphocytes for: migration, polarisation, phagocytosis, cell fusion
  • AR hyper IgE syndrome is cuased by muttions in the DOCK8 gene
53
Q

Clinical manifestations of DOCK 8 deficiency:

A
  • eczema
  • recurrent resp infections
  • severe (food) allergies
  • viral infections
  • abscesses
  • candidiasis
  • failure to thrive

Mx HSCT

54
Q

Other things seen in combined immunodeficiencies:

A
  • loss of ‘self tolerance’
    • central tolerance - thymic deletion
    • peripheral tolerance - Tregs
55
Q

Classic PID and what malignancies they are associated with:

A
  • severe combined immunodeficiency - lymphoma
  • Wiskott-Aldrich syndrome - lymphoma
  • CD40 ligand deficiency - HCC
  • DOCK 8 deficiency
  • X-linked lymphoproliferative disease - lymphoma
  • DNA repair defects - lymphoma
  • common variable immunodeficiency - lymphoma
56
Q

Deficiencies of the innate immune system:

A
  • phagocyte disorders:
    • reduced numbers
    • reduced function
  • NK cell defects
  • cytokine deficiencies
  • toll-like receptor defects
  • complement deficiency
57
Q

Phagocyte (neutrophil) defects:

A
  • defects in neutrophils (function or number)
    • account for nearly 20% PIDs
    • include chronic granulomatous disease, leukocyte adhesion deficiency, Chediak-Higashi, Griscelli syndrome, neutrophil. granule deficiency, severe congenital neutropenia (Kostmann syndrome) and X-linked neutropenia
58
Q

What goes wrong to cause chronic granulomatous disease?

A
  • defect in NADPH oxidase complex resulting in inability to produce respiratory burst (and generation of oxygen free radicals would normally kill the microbe)
  • several components of NADPH complex encoded by different genes
    • you can get X-linked and AR forms
  • failure to kill micro-organism leads to granuloma formation
59
Q

What are the key features of chronic granulomatous disease?

A
  • early presentation - usually
  • abscess and deep-seated infections of lungs, lymph nodes, liver (few diseases present with liver abscesses so important to consider CGD) and bones
  • catalase positive bacteria - staphlococcus, klebsiella, serratia & burkholderia
  • fungal infections - Aspergillus
  • inflammatory bowel disease
60
Q

How do you diagnose CGD?

A
  • determine phagocyte oxidase activity by measuring reduction of a fluorescent dye such as dihydrodamine (DHR)
  • DHR reduction will produce a quantitive chaneg in fluorescence that can be measured by flow cytometry
  • Request: neutrophil oxidative burst
  • alternative diagnostic test:
    • nitro blue tetrazolium (NBT) test

Other things to look for:

  • culture for bacteria and fungi
  • evidence of gut inflammation
  • evidence of obstruction e.g. urethra secondary to granuloma
  • total number of neutrophils are normal on FBC
61
Q

How do you treat chronic granulomatous disease?

A
  • prophylactic antibiotics
  • prophylactic anti-fungals
    • ideally diagnosis is made at a very young age so that these can be started before complications of persistent infection –> if family history it is very important to screen at burth
  • interferon gamma
  • bona marrow transplant (mainstay of curative therapy)
  • ? role for gene therapy
62
Q

Examples of other neutrophil defects of killing:

A
  • myeloperoxidase deficiency
  • G6PD deficiency
  • both present with similar presentations to CGD but milder forms
    • confirm by measuring enzyme levels
63
Q

Leukocyte adhesion deficiency:

A
  • rare
    • normal number of leukocytes
    • normal oxidative burst but:
    • inability of leukocytes to localise to sites of inflammation due to defective adherence mechanisms
  • three types
  • clinical manifestations vary but all have a defect in CD18 present on surface of leukocytes
  • complete deficiency of CD18 results in death early in life but those with partial defects benefit from prophy;actic and acute antibiotics
  • BMT may be required (curative)
64
Q

Other neutrophil defects: chediak-higashi syndrome

A
  • abnormal neutrophil granules and defective killing
  • occulocutaneous albinism, neurological symptoms and increased pyogenic infections
  • can develop unchecked inflammation
  • HSCT can cure immunological defects but not neurological symptoms
65
Q

Other defects of neutrophils: griscelli syndrome

A
  • global pigmentary dilution with silvery grey hair
  • abnormal management of intracellular granules
  • pyogenic iinfeciotns
  • HSCT can cure immunologic abnormalities
66
Q

Name secondary causes of neutropenia

A
  • infection
  • immunosuppression
  • malignancy
67
Q

Name primary causes of neutropenia:

A
  • severe congenital, cyclic or X-linked
  • presents as:
    • septicaemia, bacterial resp infections, soft tissue infections, gingivostomatitis, periodontitis and oral/vaginal/rectal ulcerations
    • severity parallels the deficiency
68
Q

How to diagnose neutropenia:

A
  • neutrophil count on FBC
  • need to determine if persistent or cyclical drop every 21 days
69
Q

Name the secondary cause of NK defects:

A
  • meds, malignancy, infection
70
Q

Name the primary causes of NK deficiency:

A
  • reduced numbers/absent
    • GATA2 (a haematopoietic transcription factor) deficiency
  • reduced function/normal number
71
Q

What are the key features of NK deficiency?

A
  • patients present with exess of herpes viral infections
    • e.g. VZV, CMV, EBV and HSV
  • unusual features of HPV - excess malignancy
72
Q

Describe type 1 cytokine defects:

A
  • autosomal recessive
  • increased susceptibility to mycobacterial disease
  • patients with IL-12 deficiency also develop susceptible to salmonellosis
73
Q

Diagnosis of type 1 cytokine defects:

A
  • measurement of cytokine levels (specialist tests)
  • IFN-gamma levels low in IL-12 deficiency
  • raised in IFN-gamma receptor deficiency
74
Q

What is the treatment of type 1 cytokine deficiency?

A
  • antimycobacterial regimens
  • prophylaxis
  • IFN-gamma
  • HSCT
75
Q

Toll-like receptor function defects:

A
  • TLRs
    • = pattern recognition receptors for lots of molecules (self and non-self) that contain danger signals
    • key initiators of innate immune response
  • if IRAK-4 and MyD88 pathway affected - patients susceptible to pyogenic organisms
  • investigations (specialised)
    • measure production of cytokines after exposure to peripheral blood mononuclear cells to TLR ligands
76
Q

Complement deficiencies:

A
  • increased susceptibility to infection
  • increased susceptibility to autoimmunity
  • hereditary angioedema
77
Q
A

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