Clincal applications of immunology Flashcards
What is a challenge in performing viral diagnostics in immunocompromised individuals?
Virology usually uses serology to detect IgM/IgG antibodies to indicate presence of viral infection -> not present in immunocompromised indviduals
What are alternatives for serology for the detection of viral infections in immunocompromised individuals?
- Viral culture
- DNA/RNA PCR
- Viral antigen detection
- T-cell responses (difficult to measure in diagnostic setting)
Which cells are infected by parvovirus B19?
Reticulocytes
What is the effect of reticulocyte infection by parvovirus B19?
Anaemia
Describe the pattern of viral load of a parvirus B19 infection in healthy individuals
Rapid rise of viral load with a high peak, rapid decline upon start of antibody response
What are the symptoms of the first stage of parvovirus B19 infection? (4)
- Fever
- Chills
- Myalgia
- Headache
(note: can also be asymptomatic)
What are the symptoms of the second stage of parvovirus B19 infection? (2)
- Rash
- Arthralgia
(note: can also be asymptomatic)
What causes the rash after parvovirus B19 infection?
Deposition of immune complexes in the skin
What causes arthralgia after parvovirus B19 infection?
Deposition of immune complexes in the joint
In which group are rash and arthralgia after parvovirus B19 infection most common?
Women of adult age
Which patients are susceptible to severe illness upon parvovirus B19 infection? Why? What kind of disease can occur?
IIndividuals with haematological conditions -> they have a high turnover of erythrocytes, and so also many reticulocytes in the blood -> high amount of cells that parvovirus B19 can infect -> higher viral load
This can result in a transient aplastic crisis
What is the problem of parvovirus B19 infections in immunocompromised individuals?
Often cannot produce an effective antibody response, allowing for chronic infection
Which therapy is often given in chronic parvovirus B19 infections in immunocompromised individuals?
IVIG
Which supportive treatment is frequently needed for chronic parvovirus B19 infections in immunocompromised individuals?
Blood transfusions due to severe anaemia
What is the downside of using IVIG for treatment of viral infections in immunocompromised individuals?
Serum antibody titres can no longer be used to guage whether an autologous immune response is starting
Which diagnostic tool is used to diagnose parvovirus B19 infections in immunocompromised individuals?
PCR
How many polyomaviruses are there? Which are they?
3;
1. BK virus
2. JC virus
3. Thrichodysplasia spinulosa polyomavirus (TSPyV)
In which organ does BK virus occur? When is this a problem?
Kidney, can cause problems after kidney-Tx
What are common features of all polyomaviruses? (2)
- All are latent
- All are highly pevalent in the population
What disease do polyomaviruses cause in healthy populations?
No disease
Trichodysplasia spinulosa polyomavirus can give a unique syndrome under certain circumstances. What are these circumstances?
Primary TSPyV infection in severely immunocompromised individuals, usually post-Tx
Latent patients do not experience this syndrome
What is the danger of JC virus in immunocompromised individuals?
Can cause progressive multifocal leukoencephalopathy (PML), a severe form of encephalitis
Which populations are at risk of JC-mediated progressive multifocal leukoencephalopathy (PML)? (3)
- Haematological malignancies
- Post-HTx/Lu-Tx
- AIDS (pre-cART)
Which drug caused a strong rise of JC-mediated progressive multifocal leukoencephalopathy (PML)? Why?
Natalizumab -> MS drugs preventing lymphocytes from passing the blood-brain barrier, preventing adequate surveillance of latent JC in the brain
To which viral family does cytomegalovirus (CMV) belong?
Herpesviruses
What is the no. 1 virus causing problems in Tx-patients?
CMV
What is the seroprevalence of CMV during adolescence & adulthood?
Adolescence: 40%
Adulthood: 70%, with a 1% yearly risk of primo infection
How can CMV be transmitted?
Direct & indirect contact with bodily fluids
Which bodily fluids are capable of transmitting CMV? (6)
- Saliva
- Urine
- Blood
- Breast milk
- Sperm
- Tissue fluid in solid organ tranplantation
What is a primo CMV infection? (definition)
CMV infection in a CMV-negative person
What is CMV reactivation? (definition)
Replication of latent CMV
What is CMV reinfection? (definition)
CMV-positive person infected with new CMV strain
What is recurrent CMV infection? (definition)
All CMV reactivation + reinfection
What is the clinical picture in the vast majority of healthy CMV-carriers?
Asymptomatic
What can be symptoms of CMV when it does turn symptomatic? (4)
- Mild viral syndrome
- Guillain-Barré syndrome (rare)
- Hepatitis (rare)
- Lymphoproliferative disease (rare)
What is CMV end-organ disease? (definition) In which population does it occur?
Organ dysfunction due to CMV replication in that organ
Occurs in transplant patients
Which organs can be affected by CMV end-organ disease? How? Which are most common? (8)
- Brain: encephalitis
- Eye: retinitis = common
- Lung: pneumonitis
- Stomach & intestines: gastro-enteritis (=common, mainly colitis)
- Liver: hepatitis
- Kidney: nephritis
- Bladder: cystitis
- Oesophagus: oesophagitis
What are the diagnostics of CMV end-organ disease? (3)
- Characteristic cytopathic effect in pathology
- Immunohistochemistry
- Quantitive CMV PCR in plasma (supportive)
What is the characteristic cytopathic effect of CMV?
Owl eyes
What is CMV syndrome? (definition)
Fever + bone marrow suppression due to CMV infection
What is the effect of bone marrow suppression in CMV syndrome?
Neutropenia & thrombopenia
What is CMV disease? (definition)
All CMV end organ disease + CMV syndrome
Which situations give high, intermediate and low risk of CMV infection after solid organ transplantation?
High risk: donor+/recipient-
Intermediate risk:
-Donor+/recipient+
-Donor-/recipient+
Low: donor-/recipient-
Which situations give high, intermediate and low risk of CMV infection after HSCT?
Recipient+ = high risk
Recipient- = low risk
How is CMV prevented after transplantation?
Prophylactic use of antivirals
What is the incidence of CMV reactivation & CMV disease in allo-HSCT?
CMV reactivation: 2/3 of patients (measured in blood)
CMV disease: 1/3
What is the incidence of CMV reactivation & CMV disease in auto-HSCT?
CMV reactivation: 40%
CMV disease: <5%
Which class of drugs are used for the prophylactic & treatment of herpesviruses, including CMV?
Nucleoside analogues
Which drugs are used in the treatment of CMV? (3)
- (Val)ganciclovir
- Cidofovir
- Foscarnet
What is the downside of the use of antivirals for herpesviruses?
All have quite high toxicity
Which three strategies are there for the deployment of CMV-antivirals post-Tx?
- Prophylaxis = treat regardless of CMV DNA in blood
- Pre-emptive therapy = only treat when CMV DNA in blood rises
- Therapy = only treat upon CMV disease
What is a new development surrounding CMV diagnostics?
The use of cell-mediated immunity assays to predict CMV disease risk after stopping prophylaxis
What is IVIG?
Intravenous immunoglobulin = human IgG pooled from a large number of donors
Which isotypes of antibodies can be found in IVIG?
Mainly IgG with trace amounts of IgM & IgA
Many % of the IgG in IVIG is monomeric, and how much is dimeric?
95% monomeric, 5% dimeric
How many % of the IgG in IVIG is composed by each of the subclasses of IgG?
IgG1 = 55-70%
IgG2 = 30-45%
IgG3 = 1-4%
IgG4 = 0,5%
What is the estimated variety of antibodies in a dose of IVIG?
10^9
What is an alternative method of administered antibodies when IVIG is not an option?
SCIg = subcutaneous immunoglobulins
What are advantages of SCIg over IVIG? (2)
- Can be given in an at-home setting
- Has a depot function -> slow release of antibodies
Which two IVIG regimens are there?
- Low dose IVIG: 0,3-0,5 g/kg
- High dose IVIG: >0,6 g/kg
What is the application of low-dose IVIG?
Replacement for patients with primary IgG deficiencies
What is the application of high-dose IVIG?
Immunomodulation
For which immunomodulatory goals is high-dose IVIG used? (3)
- Anti-inflammatory therapy for auto-immune diseases
- Prophylaxis/treatment of antibody-mediated rejection after kidney transplantation
- Hyperimmunoglobulins to target specific diseases
In which instances are hyperimmunoglobulins (form of IVIG) used? (3)
- Antiviral therapy against HBV (HBIG)
- Antiviral therapy against CMV (CMV-Ig)
- Rho(D) immunoglobulins for Rh- mothers carrying Rh+ childeren
What are FDA-approved indications of IVIG? (7)
- Primary immunoglobulin deficiency
- Chronic lymphocytic leukaemia (CLL)
- Kawasaki’s disease
- Idiopathic thrombocytopenic purpura (ITP)
- Multifocal motor neuropathy (MMN)
- Chronic inflammatory demyelinating neuropathy (CIDP)
- Dermatomyositis
How many off-label uses are there for IVIG?
~150
Why is there a shortage in IVIG?
Recent high demand in the fields of haematology & neurology
What is Kawasaki’s disease?
Vasculitis of unkown aetiology, causing necrosis of medium-sized vessel walls
In which age group does Kawasaki’s disease primarily occur?
Children <5
What are the symptoms of Kawasaki’s disease? (4)
- High fever
- Red eyes
- Strawberry tongue
- Swollen lymph nodes
What is a severe complication of Kawasaki’s disease?
Coronary artery aneurysms
What is the treatment of Kawasaki’s disease? (2)
- First: high dose acetyl salicylic acid to suppress inflammation
- Followed by high-dose IVIG
What is immune thrombocytopenic purpura (ITP)?
Thrombocytopenia due to antibodies against thrombocytes
What is the aetiology of immune thrombocytopenic purpura (ITP)?
Unknown
What are the symptoms of immune thrombocytopenic purpura (ITP)? (3)
- Bruising/purpura
- Nose bleeding
- Spontaneous haemorrhages
What are severe complications of immune thrombocytopenic purpura (ITP)? (3)
- Intracerebral haemorrhage
- Gastrointestinal bleedings
- Other internal bleedings
What is the therapy of immune thrombocytopenic purpura (ITP)?
Start with high dose corticosteroids, if insufficient: high dose IVIG
What is Guillain-Barré syndrome (GBS)?
Acute inflammatory demyelinating polyneuropathy affecting peripheral nerves
What are the symptoms of Guillain-Barré syndrome (GBS)?
Paralysis of feet, hands and or/trunk
What is a life-threatening complication of Guillain-Barré syndrome (GBS)?
Paralysis of breathing muscles
How many % of Guillain-Barré syndrome (GBS) patients require artificial ventilation?
25%
What is the aetiology of Guillain-Barré syndrome (GBS)?
Antibodies against bacterial pathogens cross-react to myelin sheath of periheral nerves
What is the treatment of Guillain-Barré syndrome (GBS)?
High dose IVIG
Why are there large differences in efficacy of IVIG in Guillain-Barré syndrome (GBS) patients?
Large inter-patient variation in IVIG titres due to catabolism
What are lower levels of IVIG in serum in Guillain-Barré syndrome (GBS) correlated with?
Worse recovery
Why is a second round of IVIG not recommended for Guillain-Barré syndrome (GBS) patients?
Does not lead to faster recovery, but does cause more side effects
How can endogenous IgG be distinguished from IVIG?
Using allotypes of antibodies
What is an antibody allotype?
Differences due to SNPs in the constant domain of antibodies
What are the two parts of an antibody that can have anti-inflammatory actions?
- F(ab)2
- Fc
What are the F(ab)2-dependent anti-inflammatory modes of action of IVIG? (2)
- Neutralization of antibodies, cytokines, soluble receptors, membrane-bound receptors & toxins
- Cell depletion
What are the Fc-dependent anti-inflammatory modes of action of IVIG? (5)
- Saturation of FcRn
- Inhibition of complement
- Blocking of activating FcγR
- Modulation of immune cell activation
- Expansion of regulatory T-cells
How does the FcγRI differ from the other FcγRs?
FcγRI is the only high-affinity receptor -> monomeric immunoglobulins are able to bind to and activate this receptor
How does the FcγRIIB differ from the other FcγRs?
FcγRIIIB is the only inhibitory FcγR
How can IVIG block activating FcγRs?
By saturating the FcγRs, pathogenic antibodies can no longer bind these receptors
Which cell types are susceptible to blocking of their FcγRs by the Fc-domain of IVIG? (3)
- Macrophages
- NK-cells
- Neutrophils
In which disease has the blocking of FcγRs by IVIG been shown?
ITP
How was FcγR blocking by IVIG Fc-domain shown in ITP mouse models?
Mice treated with anti-thrombocyte antibodyes, and co-treated with:
-Nothing -> thrombocyte depletion
-IVIG -> partial prevention of thrombocyte depletion
-IVIG F(ab)2 -> thrmbocyte depletion
So: only IVIG with an Fc-domain can prevent thrombocyte depletion
What is an important factor for the capacity of IVIG to block FcγRs?
Glycosylation
Which glycosylation of serum IgG causes a weak binding to FcγRs? What is the effect of this?
Which glycosylation of serum IgG causes a strong binding to FcγRs? What is the effect of this?
Gal-, Fuc+ = weak binding -> auto-immunity & inflammation
Gal+, Fuc- = strong binding -> immunomodulation
What is the advantage of Gal+, Fuc- antibodies?
Can strongly bind to FcγRs, displacing auto-antibodies
How can saturation of the FcRn have an immunomodulatory effect?
FcRn recycles auto-antibodies -> by saturating this receptor, catabolism of auto-antibodies is sped up
What is the mechanism of IgG catabolism by the FcRn? (3)
- Uptake in the endosome of endothelial cells, followed by lysosomal degradation of unbound IgG
- FcRn can bind IgG in endosomes at low pH
- FcRn is transported to the cell surface and releases IgG in pH-neutral environment
How can IVIG cause immunomodulation by macrophages?
By causing upregulation of the inhibitory FcγRIIB
What is the effect of upregulation of FcγRIIB on macrophages?
Decreased phagocytosis of opsonized cells
The majority of FcγRs on the cell surface are normally [activating/inhibitory]
Majority is activating
Which mechanism of action of FcγRIIB upregulation by IVIG was disocvered in mice?
- IVIG binds to macrophages in the spleen, inducing IL-33 production
- IL-33 induces IL-4 & IL-13 production in macrophages
- IL-4 upregulates FcγRIIIB on macrophages
To which lectin on macrophages in the spleen of mice does IVIG bind? What is the analogous lectin in humans?
Mice: SIGN-R1
Humans: DC-sign
True or false: IVIG can cause upregulation of the FcγRIIB in humans
False; this mechanism has been shown in mice, but not in humans -> it causes upregulation of FcγRIIIB (which is activating)
Which discovery makes it unlikely that the mechanism of action of IVIG in humans is caused by upregulation of the FcγRIIB on macrophages in the spleen?
IVIG also has effect in splenectomized individuals
How was the expansion of Tregs by IVIG discovered in mice?
Administration of IVIG in an EAE mouse-model for MS causes:
1. Less severe EAE
2. Higher % of Tregs in CD4+ subset
3. Effect of IVIG disappears when Tregs are depleted
What is the effect of IVIG on Tregs in humans?
- No increase in Treg numbers
- Increased Treg activity
- Increased Treg suppressive capacity
Which two factors point to increased Treg activity after IVIG administration in humans?
- HLA-DR expression increases
- FoxP3 expression increases
What are the hypotheses for the upregulation of Treg activity by IVIG? (4)
- IVIG induces production of IL-33 by macrophages -> Treg expansion
- IVIG binds to DC-inhibitory receptor -> co-stimulatory signals that induce Tregs
- IVIG induces PGE2 which induces Treg expansion
- IVIG is internalized by APCs and presented to T-cells in a non-activating/inflammatory environment (no costimulation) -> Tregs
What are the general advantages of IVIG as a treatment? (3)
- No acute adverse effects
- No long-term adverse effects
- Long half-life -> only 1 treatment per 3-6 weeks
What are the general disadvantages of IVIG as a treatment? (4)
- IV administration with long infusion times
- Variation between brands & lots of IVIG
- High costs
- Limited amount of safe, virus-free human plasma can lead to shortages
Which developments are underway to increase IVIG effectivity and/or reduce the needed amounts of IVIG? (3)
- Synthetic IVIG: trimerig IgG Fc blocks binding of pathogenic immune complexes to FcγR
- IVIG with modified glycosylation to control its effects
- Human IgG1 Fc/antibody that binds FcRn -> simulates FcRn blocking effect of IVIG
