IMMUNO: Primary Immunodeficiency Flashcards
List the categories of autoimmune disease.
Overactivation:
- Auto-inflammatory disease
- Autoimmune disease
- Allergic disease
Underactivation:
- Primary immunodeficiency
- Secondary immunodeficiency
How are immunodeficiencies classified?
- Primary - inherited - clinically important immunodeficienciesare rare (1:10,000 live births)
- Secondary - acquired - infection, malignancy, drugs, nutritional deficiencies (common)
- Physiological
- Neonates
- Pregnancy
- Older age
What clinical features are suggestive of immunodeficiency?
- Two major or one major and recurrent minor infections in one year
- Atypical organisms, unusual sites, poor response to treatment
- Primary immune deficiency in the family, presenting at young age, failure to thrive
What can primary immunodeficiency be split into?
- Innate system
- Adaptive system
List the cells and soluble components of the innate immune system.
- PMNs - neutrophils, eosinophils, basophils
- Monocytes and macrophages
- NK cells
- Dendritic cells
- Complement, APPs, cytokines and chemokines
Name two types of receptors present on neutrophils and two functions.
Receptors:
- Cytokine/chemokine receptors - homing to site of infection
- Genetically encoded receptors - PRRs (e.g. toll-like receptors or mannose receptors) which recognise PAMPs (e.g. sugars, DNA, RNA).
- Fc receptors - detection of immune complexes
Functions:
- Phagocytosis of pathogens
- Secretion of cytokines and chemokines
What is released by granulocytes?
Produced in BM and migrate quickly to site of injury and release enzymes, histamine, lipid mediators of inflammation from granules.
Where are these types of macrophages found?
- Kupffer cell
- Mesangial cell
- Osteoclast
- Sinusoidal lining cell
- Alveolar macrophage
- Microglia
- Histiocyte
- Langerhans cell
- Macrophage like synoviocytes
Liver
Kidney
Bone
Spleen
Lung
Neural tissue
Connective tissue
Skin
Joints
What are monomuclear cells?
Monocytes and macrophages - produced in BM and migrate to tissues where they differentiate from monocytes into macrophages and are capable of presenting processed antigen to T cells
Describe how the innate immune system contributes to overcoming infections.
- Pathogen in tissue
- Increased expression of adhesion molecules
- Neutrophils released and home to site of infection
- Phagocytosis by neutrophils
- Engulfment by macrophages and presentation to T cells
- Cell death and pus formation
Summary of phagocyte deficiency immunodeficiency.
What are the four types of phagocyte deficiency?
- Failure to produce neutrophils
- Defect of phagocyte migration
- Failure of oxidative killing mechanisms
- Cytokine deficiency
List 3 types of failure to produce neutrophils. State which are autosomal recessive/dominant.
- Reticular dysgenesis - AR severe SCID (most severe)
- Kostmann syndrome - AR severe congenital neutropenia
- Cyclic neutropenia - AD episodic neutropenia every 4-6 weeks
Types of mutations (don’t need to learn):
- AK2 (mitochondrial enzyme)
- HAX1
- ELA-2
Name a defect of phagocyte migration.
Leukocyte adhesion deficiency - deficiency of CD18 (beta2 integrin subunit) which means that the neutrophil cannot bind to ICAM-1 on endothelial cells via CD11a/CD18 (LFA-1) = NO EXIT FROM BLOODSTREAM
What are neutrophil levels in leukocyte adhesion deficiency?
Very high in bloodstream (because cannot exit into tissues)
No pus formation
Name a failure of oxdative killing mechanims in neutrophil-mediate immunodeficiency. What is the pathophysiology of this?
Chronic granulomatous disease
No respiratory burst due to deficiency of one or components of NADPH oxidase –> unable to generate ROS –> impaired killing –> neutrophils/macrophages accumulate causing excessive inflammation –> granuloma formation and lymphadenopathy/hepatosplenomegaly
Name and describe two investigations for chronic granulomatous disease.
First step is to activate the neutrophils which should have a respiratory burst and produce hydrogen peroxide, followed by…
Nitroblue terazolium (NBT) test - NBT is a dye which changes colour yellow to blue if it interacts with hydrogen peroxide
Dihydrorhodamine (DHR) flow cytometry test - DHR is oxidised to rhodamine which is fluorescent after hydrogen peroxide
Which types of infections are common in cytokine deficiency mediated phagocyte deficiency?
IL-12- IFNgamma network deficiency causes mycobactrial infection
Name a type of cytokine deficiency which can cause phagocyte-mediated immunodeficiency.
IL12, IL-12R, IFNgamma, IFNgamma-R deficiencies
IL12-IFNgamma is activated by infection:
- Activated macrophages produce IL-12
- IL-12 stimulates T cells to produce IFN-gamma
- IFN-gamma feeds back to neutrophils and macrophages to stimulate:
- TNF production
- NADPH oxidase activation and oxidatiev pathways
What are the clinical complications of phagocyte deficiency?
Recurrent infections –skin / mouth
- Bacterial infections
- Staphylococcus aureus
- Enteric bacteria
- Fungal infections
- Candida albicans
- Aspergillus fumigatus and flavus
- Mycobacterial infection
- Mycobacterium tuberculosis
- Atypical Mycobacteria
What is the management of pahgocyte deficinecy immunodeficiency?
Aggressive management of infection
- Infection prophylaxis - prophylactic antibiotics (septrin i.e. co-trimoxazole), anti-fungals (itraconazole)
- Treatment with oral/IV antibiotics
Definitive therapy
- HPSC transplant - replaces the defective population
- Specific treatments e.g. IFN-gamma therapy for CGD
What is the function of NK cells?
Migrate from blood into inflamed tissues
Have an inhibitory receptor which recognised HLA class I to prevent inappropriate activation
Have an activatory receptor including natural cytotoxicity receptors to recognise heparan sulfate proteoglycans
Malignant/virus infected cells fail to express HLA class I so NK cells cause their lysis via (1)cytotoxicity, (2)cytokine secretion, (3)contact dependent regulation
Name and decribe two types of NK deficiencies.
-
Classical NK deficiency
- Absence of NK cells within peripheral blood
- Abnormalities described in GATA2or MCM4genes in subtypes 1 and 2
-
Functional NK deficiency
- NK cells present but function is abnormal
- Abnormality described in FCGR3Agene in subtype 1
Which infections are most commonly associated with NK cell deficiencies?
- Intracellular virus infections e.g. HHV infections
- HPV - including malignancy (HPV associated cancers)
What is the management for NK cell deficiencies?
- Prophylactic antivirals e.g. acyclovir or gancyclovir
- Cytokines such as IFN-alpha to stimulate NK cytotoxic function
- HPSC transplantation if severe
Match these up.
- leukocyte adhesion deficiency
- CGD
- Kostmann syndrome
- IFN-gamma R deficiency
- Classical NK cell deficiency
Where is complement produced and how many components are there?
>20 tighly regulated, linked proteins produced in the liver
Draw the complement cascade.
What activates the classical pathway?
- Activated by formation of antibody-antigen immune complexes
- Contact results in change in antibody shape, exposing the binding site for C1
- C1 binds to the antibody site which causes activation of the vascade
Dependent upon activation of acquired immune response (antibody)
What are the components of the classical pathway?
C1, C2, C4 –> C3 —> C5-C9 (final common pathway) –> membrane attack complex
What activates the mannose binding lectin pathway? What is its advantage over classical?
- Activated by direct binding of MBL to microbial cell surface carbohydrates
- This stimulates the classical pathway C2 and C4 (NOT C1) –> C3 —> C5-9
Not dependent on the acquired immune response
What activates the alternate pathway? What factors are involved? Which is the control protein?
- Activated by bacterial cell wall components e.g. lipopoolysaccharise of gram negative bacteria, teichoic acid of gram positive bacteria.
- Involves factors B, D and properidin.
- Factor H is the control protein (usually -ve regulated to regulate spontaneous activation)
Not dependent on the acquired immune response.
What is the function of activation of C3?
Triggers formation of the membrane attack complex via C5-9
MAC causes membrane lesions
List 5 functions of complement.
- Increases vascular permeability and cell trafficking to site of inflammation
- Activates phagocytes
- Opsonisation of pathogens to promote phagocytosis
- Promotes clearance of immune complexes
- Punches holes in bacterial membranes
What bacterial infections are those with complement deficiency most susceptible to?
Especially those by encapsulated bacteria:
- Neisseria meningitides (esp in properidin and C5-9 deficiency)
- Haemophilus influenzae
- Streptococcus pneumoniae
What are the results of C1q and C2 deficiency?
Susceptibility to SLE because…
- failure of phagocytosis –> dead cells and nuclear debris
- failure to clear immune complexes –> immune complex deposition in blood vessels –> small vessel vasculitis
What are the results of C5-9 and properidin deficiency?
Susceptibility to Neisseria meningitides
What are the consequences of MBL pathway deficiency?
MBL2 mutations are common but NOT USUALLY ASSOCIATED WITH IMMUNODEFICIENCY
How does SLE contribute to immunodeficiency?
Persistent activation of the classical pathway leads to immune complex deposition and therefore low C3 and C4
NB: deficiency of C1q and C2 increases susceptibility to SLE
What is the name for auto-antibodies against components of the complement pathway?
Nephritic factors = auto-antibodies against components of the complement pathway
What are the effects of nephritic factors on the complement cascade?
Nephritic factors stabilise C3 convertases –> C3 activation and consumption
- Often associated with glomerulonephritis (classicaly membranoproliferative)
- Also associated with partial lipodystrophy (fat lost from upper body)
How can auto-immune disease lead to complement deficiency?
- SLE - leads to overconsumption of C3, C4
- Nephritic factors - anti-C3 convertase so C3 overactivation leads to low C3
NB: C3 and C4 are routinely measured in blood tests
What are two functional complement tests?
CH50 - tests for C1, C2, C4, C3, C5-9
AP50 - tests for C3, C5-9
Fill in the blanks for C3/4 levels and CH50 and AP50 test results for each complement deficiency.
- C1q deficiency leads to abnormal CH50 because classical pathway is not activated in the right way but normal AP50 because still activation alternate.*
- Properidin is involved in the alternate pathway.*
- C9 is part of classical and alternate as it is at the end.*
How do you manage patients with complement deficiencies?
- Vaccination - pneumovax, meningovax, HIB vaccines especially
- Prophylactic antibiotics
- Treat infections aggressively
- Screen family members
Match up the answers.
1 - 1
2 - 2
3 - 4
What is a primary lymphoid organ? Where are B and T cells formed and where do they mature?
Primary lymphoid organ - organs involved in lymphocyte development
B cells - develop and mature in BM
T cells - develop in BM and mature in thymus
What is the more severe form of SCID?
Reticular dysgenesis - mutation in the AK2 enzyme (adenylate kinase 2). HSC do not differentiate into myeloid/lymphoid lineages.
What are the consequences of reticular dysgenesis?
Fatal in early life unless corrcted with BM transplantation
There is failure of production of lymphocytes, neutrophils, monocytes/macrophages, platelets.
What is the most common SCID?
SCID because it is combined B and T cell deficiency.
X linked SCID - makes up 45% of all SCIDs
What is the mutation in X linked SCID?
Mutation of common gamma chain on chromosome Xq13.1 - if signalling in this chain is affected it affects downstream signalling via IL-2, IL-4, IL-7, IL-9, IL-15 and IL-2. Inability to respond to cytokines causes:
- early arrest of T and NK cell development and production,
- and immature B cells
What are the lymphocyte levels in X-linked SCID?
Phenotype
- Very low or absent T cell numbers
- Very low or absent NK cell numbers
- Normal or increased B cell numbers but low Igs
How common is ADA deficiency? What is the pathogenesis and phenotype?
- 5% of all SCID
* Adenosine Deaminase Deficiency - enzyme required for cell metabolism in lymphocytes
Phenotype
- Very low or absent T cell numbers
- Very low or absent B cell numbers
- Very low or absent NK cell numbers
What protects the neonate in the first 3 months of life in SCID?
What are the clinical features of SCID?
- Unwell by 3 months of age
- Infections of all types
- Failure to thrive
- Persistent diarrhoea
- Unusual skin disease - colonisation of infant’s empty bone marrow by maternal lymphocytes and graft versus host disease
- Family history of early infant death
What is the difference in function of CD4+ and CD8+ T cells?
Describe the process of central tolerance and selection in T cell maturation.
- Only T cells which have intermediate affinity for HLA are positively selected (10%) - those with low affinity for HLA are not selected, and high affinity are negatively selected to avoid autoreactivity.
- Those with intermediate affinity for HLA class I differentiate into CD8+, those with intermedate affinity for HLA class II differentiate into CD4+ cells
What are CD8+ T cells also called? What are their functions?
Cytotoxic cells
- Recognise peptides derved from INTRACELLULAR proteins in association with HLA class I
- Kill cells via perforin, granzymes and expression of Fas ligand
- Secrete cytokines e.g. IFNgamma, TNFalpha
Defence against tumours and viral infections
What are 3 functions of CD4+ ‘helper’ T cells?
- Recognise peptides derived from extracellular proteins presented on HLA class II molecules (HLA-DR, HLA-DP, HLA-DQ)
- Provide help for development of full B cell responses
- Povide help for development of some CD8+ T cell responses
(2 and 3 are immunorregulatory functions via cell:cell or cytokine interactions)
Briefly describe the polarising factors and function of these cells:
- Th1
- Th17
- Treg
- TFh
- Th2
- TPh
Which CD4+ cells are polarised by IL-4 and IL-6 and effector profile of IL-4/5/10/13?
Helper T cells
Which CD4+ cells are polarised by IL-6/1b/TNFa and have effector functions of IL-2/10/21?
TFh
Which CD4+ cells are polarised by IL-12 and IFNg and have effector functions of IL-2/10, IFNg and TNF?
Which cells are polarised by IL-6/TGFb and have effector functions of IL-17/21/22?
Th1
Th17
Which CD4+ cells are polarised by IL-23 and TGFb and have effector functions of IL-10, FOXP3 and CD25?
Treg
What is the mutation in DiGeorge syndrome? Is it inherited or sporadic?
22q11.2 delection syndrome - TBX1 may be responsible for some features but most cases are sporadic rather than inherited
Developmental defect of pharyngeal pouch
What are the features of 22q11.2 deletion syndrome?
- High forehead
- Low set, abnormally folded ears
- Cleft palate
- Hypocalcaemia
- Oesophageal atresia
- Underdeveloped thymus
- Complex congenital heart disease
Normal B cell numbers
Reduced number of T cells - homeostatic proliferation with age so immune function usually only mildly impaired and improves with age
What happens if MHC class II is not expressed on cells of the thymus? What is this condition called?
There is no formation of CD4+ T cells which recognise peptides from extracellular proteins in conjunction with MHC class II
–> Bare lymphocyte syndrome type 2
Which regulatory proteins contain mutations in bare lymphocyte syndrome type 2? What phenotype does this cause?
Regulatory factor X or Class II transactivator
–> absence of MHC II molecules
Phenotype:
- Deficiency of CD4+ cells
- Normal number of CD8+ cells
- Low or normal IgG and IgA due to lack of CD4+ T cell help in germinal centres
BLS type 1 is where MHC I is absent.
Why are IgA and IgG levels low in BLS type 2?
No CD4+ T cells which help with isotype switching to change IgM into IgA and IgG in the germinal centres
What are the clinical features of BLS?
- Unwell by 3 months
- Infections of all types
- Failure to thrive
- FH of early infant death
Name 4 types of defects of T cell effector function.
Defects in:
- cytokine production - IFN
- cytokine receptors - IL-12
- cytotoxicity
- T-B cell communication (CD40 ligand deficiency)
What are the clinical features of T lymphocyte deficiency?
- Viral infections e.g. CMV
- Fungal infections e.g. pneumocytsic, cryptosporidium
- Some bacterial infections esp intracellular organisms e.g. TB, salmonella
- Early malignancy
What are the main investigations for T cell deficiencies?
- Total white cell count and differential - remember that lymphocyte counts are normally much higher in children than in adults
- Lymphocyte subsets - quantify CD8 T cells, CD4 T cells as well as B cells and NK cells
- Immunoglobulins - if CD4 T cell deficient
- Functional tests of T cell activation and proliferation - useful if signalling or activation defects are suspected
- HIV test
Which markers can be used for B and T cell sorting FACS?
T cells - CD8 and CD4 marker OR CD3 (both)
B cells - CD20
Fill in the blanks.
What is the management of T cell immunodeficiency?
- Aggressive prophylaxis/treatment of infection
- Haematopoieitic stem cell transplantation - to replace abnormal populations in SCID; to replace abnormal cells -class II deficient APCs in BLS
- Enzyme replacement therapy - PEG-ADA for ADA SCID
- Gene therapy - stem cells treated ex-vivo with viral vectors containing missing components, transduced cells have survival advantage in vivo
- Thymic transplantation - to promote T cell differentiation in Di George syndrome - cultured donor thymic tissue transplanted to quadriceps muscle
Match these up.
1, 2
2, 4
3, 3
4, 1
Describe B cell development briefly. In what form do B cells leave the BM?
IgM B cells
How is central tolerance by B cells maintained?
No recognition of seld in BM means that B cells survive and leave BM (those that recognise self are negatively selected to avoid autoreactivity)
NB: NO INTERMEDIATES
What happens to B cell upon antigen encounter?
- Early IgM response - T cell independent whereby IgM memory cells and Ab secreting plasma cells are found
-
Germinal centre reaction in lymph node with CD4+ T cell help
- Dendritic cells prime CD4+ cells
- CD4+ cells help B cells differentate (via CD40L:CD40 interaction)
- B cell proliferation, somatic hypermutation, isotype switching to IgG, A, E
–> high affinity memory cell and plasma cell production.
What are Igs made up of?
2 heavy and 2 light chains
5 types - IgA, E, G, D, M (and subclasses of IgG and IgA)
Antigen is recognised by antigen binding region Fab (V)
Effector function determined by constant region Fc (stem)
Name 3 immune components/cells which antibodies interact with.
Complement
Phagocytes
NK cells
What is the name for condition in which there is failure for preB-cells to differentiate into B cells?
Bruton’s X-linked hypogammaglobulinaemia
What is the mutation in Bruton’s X linked agammaglobulinaemia? What is the phenotype and when does it manifest?
Abnormal B cell tyrosine kinase (BTK) gene
Absence of MATURE B cells and no IgG after 3 months (ONLY IN BOYS)
What are the clinical features of X linked agammaglobulinaemia?
- Boys (present in first few years of life)
- Recurrent bacterial infection - otitis media, sinusitis, pneumonia, osteomyelitis, septic arthritis, gastroenteritis
- Viral, fungal, parasitis infections - enteroviruses, pneumocystis
- Failure to thrive
Name a B cell maturation defect. What is the inheritance pattern?
Hyper IgM syndrome (X linked recessive)
What is the mutation in Hyper IgM syndrome? Where is this expressed: B or T cells?
Mutation in CD40 ligand gene (CD40L, CD154) so that CD4+ T cells cannot offer help to B cells in germinal centres
Encoded on Xq26, member of TNF-R family
DEFECT IS ON THE T CELL
What are the antibody levels in hyper IgM syndrome?
Undetectable IgA, IgE and IgG
Elevated serum IgM
(no germinal centre development and no isotype switching)
How does hyper IgM syndrome present clinically?
In boys as with Bruton’s
Recurrent bacterial infections BUT abnormality in T cell also predisposes to PCP, AI disease and malignancy
Failure to thrive
What is the phenotype of common variable immune deficiency? (CVID) What is the pathophysiology?
Defined by (1) low IgA, IgG and IgE (–> recurrent bacterial infections,) (2) poor response to immunisation, (3) absence of other immunodeficiency
COMMON and can present in childhood or adulthood with heterogenous genetic defects
Due to failure of full differentation/function of B lymphocytes
What are the clinical features of CVID?
Adults OR children affected
Recurrent bacterial infections - pneumonia, persistent sinusitis, gastroenteritis, often with severe end-organ damage
Pulmonary disease - interstitial lung disease, granulomatous interstitial lung disease (also LN, spleen), obstructive airways disease
Gastrointestinal disease - IBD like disease, sprue like illness, bacterial overgrowth
Autoimmune disease - AIHA or thrombocytopenia, RhA, pernicious anaemia, thyroiditis, vitiligo
Malignancy - NHL
How common is IgA deficiency? What is the cause?
Prevalence high with 1:600 affected but only 1/3 are symptomatic (recurrent resp infections)
Genetic component, cause yet unknown
Which bacterial infections, toxins and viral infections are most common in antibody deficiencies/CD4 T cell deficiency?
Bacterial - staphylococcal, streptococcal
Toxins - tetanus, diptheria
Viral - enterovirus
Which investigations are used for B cell deficiencies?
- Total WCC and differential - lymphocyte counts in general are much higher in children than in adults
- Lymphocyte subsets - to quantify B cells, CD4, CD8 and NK cells
- Serum Igs and protein electrophoresis - production of IgG is a surrogate marker for CD4 T helper cell function
- Functinal tests of B cell function - measure specific Ab reponses to known pathogens/immunisations e.g. tetanus, HIB, S pneumonia; if low then immunise and repeat measurement in 6-8 weeks.
What is shown here? What condition could this be?
Gamma band shows antibodies - this one above shows absence so this could be Bruton’s
Fill in the blanks.
How do you manage B cell immunodeficiency? Is HSCT curative?
- Aggressive prophylaxis / treatment of infection
- Immunoglobulin replacement if required - derived from pooled plasma from thousands of donors; contains IgG antibodies to a wide variety of common organisms, aim of maintaining trough IgG levels within the normal range; treatment is life-long
- Immunisation - for selective IgA deficiency, not otherwise effective because of defect in IgG antibody production
HSCT not required as you can keep replacing antibodies instead.
Match these up.
1, 2
2, 4
3, 3
4, 1
