UPDATED Immuno: Primary Immune Deficiencies 2 Flashcards
What is the largest innate cell population in the blood? and what is it regulated by?
NEUTROPHIL
Continuous production by bone marrow regulated by IL-17-G-CSF axis
Where are neutrophils found?
Found bone marrow, LN, lung and spleen
What 3 things do neutrophils do?
- Eliminate pathogens
- Phagocytosis, degranulation, NETosis
- Healing and repair tissue damage
- Modulates adaptive immune responses
- Promotes T cell independent antibody production
- Enhances or suppresses T cell function
Describe the structure of a neutrophil
What are the 2 types of defects in neutrophil function?
- Binding to endothelial cells: Leukocyte adhesion deficiency syndromes (LAD)
- Generation of reactive oxygen species: Chronic Granulomatous Disease (CGD)
What are the ranges of quantitative neutrophil defects?
- 1.0-1.5 x10^9/L Mild
- 0.5-1.0 x10^9/L Moderate
- 0.2-0-5 x10^9/L Severe
- <0.2 x 10^9/L Very severe
What are the 2 quantitative neutrophil deficiency syndromes?
- Chronic benign neutropenia
- Severe congenital neutropenia
What is Chronic benign neutropenia?
- Mild (usually) or moderate neutropenia
- Common in number of different ancestry groups (Africa, Middle East)
- Asymptomatic ( should not lead to further investigation)
What is severe congenital neutropenia?
- Several conditions involving defects in neutrophil maturation
- Different mutation in Neutrophil Elastase enzyme are commonly implicated
- Present within first 3 months of life
- Susceptible to oral, cutaneous Staphylococcal (aureus, epidermidis), G- enteric bacteria (Pseudomonas aeruginosa) and fungal (candida and aspergillus)
- Life threatening infections if not recognized and treated promptly
- Genetic defects which may also involve other organ systems and can pre-dispose to haematological malignancy (MDS and AML)
- G-CSF support and stem cell transplantation for high risk individuals
What is leukocyte adhesion deficiency? and what is it caused by?
Caused by failure of neutrophil migration
* due to deficiency of CD18 (β2 integrin subunit)
CD11a/CD18 (LFA-1) is expressed on neutrophils, binds to ligand (ICAM-1) on endothelial cells and so regulates neutrophil adhesion/transmigration
Lack of expression of adhesion molecules results in failure to exit from the bloodstream
* delayed separation of umbilical cord
* very high neutrophil counts in blood (20-100 x106/L)
* absence of pus formation
* Haematopoietic stem transplantation
What is chronic granulomatous disease and what is it caused by?
- Absent respiratory burst
- due to an inability to generate oxygen free radicals results in impaired killing, NETosis.
- caused by deficiency of one of components of NADPH oxidase
What is chronic granulomatous disease characterised by?
- Skin, lymph node, liver, bone, chest bacterial , fungal, TB and NTM infections
- Excessive inflammation
- Increased NF-κβ and IL-1β activation
- Macrophage infiltration and granuloma
- Gastro-intestinal and genitourinary inflammatory disease
What is the management of chronic granulomatous disease?
- Cotrimoxazole and itraconazole prophylaxis
- Adjunctive IFN-, Stem cell and gene therapy
What are some Investigation of neutrophil IEI syndromes?
- Immunoglobulins
- Lymphocyte subsets
- Bone marrow biopsy
- Neutrophil function assay
- Neutrophil oxidative burst
- Stimulate neutrophils and measure hydrogen peroxide
- DHR-123 assay: DHR-13 is oxidised to rhodamine which is strongly fluorescent, following interaction with hydrogen peroxide
- Genetic neutrophil panels
What is a complement pathway, and what does it do?
- Complement is a protein network
- Complement cascade proteins (C1 to C9)
- Complement regulatory protein (C1 inhibitor, Factors B,D, P, H I, CD46, CD55, CD59)
- Complement receptors (CR1-4)
- Complement function
- Induction of acute inflammatory responses (C3a, C5a)
- Opsonisation of pathogens (C3b)
- Removal of immune complexes (C1q-CR1)
- Control of Neisseria infection (C5-9)
- Regulation of B and T cell immune responses (C3d)
What can activate C3 thus activating the complement pathway?
- Antigen-IgG (Classical)
- Carbohydrates (MBL)
- Bacterial cell wall (alternate)
What are some complement protein deficiencies, and what can they cause?
What are some deficiencies of complement regulatory proteins and what do they cause?
What are some investigations of complement function?
- FBC
- Serum immunoglobulin
- Lymphocyte subsets
- C3 and C4
- Functional complement tests
- CH50 classical pathway
- AP50 alternative pathway
- Complement genetic test
What is the management of patients with complement cascade protein deficiencies?
- Vaccination
- Boost protection mediated by other arms of the immune system
- Tetravalent Meningococcal vaccine , Pneumovax and HIB vaccines
- Prophylactic antibiotics
- Treat infection aggressively
- Screening of family members
What are primary lymphoid organs?
Organs involved in lymphocyte development
What are the 2 primary lymphoid organs?
- Bone marrow
- Thymus
What does the bone marrow and thymus do as primary lympohoid organs?
Bone marrow
* Lymphoid progenitors progenitors
* Site of B cell development and maturation
* Negative selection B cell
Thymus
* Site of T cell lineage commitment
* Self-MHC-peptide positive section
* Negative selection
* CD4 CD8 and CD4 T regulatory cell development
* Most active in the foetal and neonatal period, involutes after puberty ? Active adults
Outline Lymphoid
Development
What is severe combined immune deficiency (SCID)?
Absence or dysfunction of T cells affecting both cellular and humoral immunity
SCID results from defects in the generation of lymphoid precursors in bone marrow
What is the molecular basis for SCID?
Mechanistic basis for SCID: more than 20 diseases
- Metabolic diseases which inhibit lymphocyte development
- Absent or impaired cytokine signal transduction pathways
- Defects in V (D)J recombination resulting in failure to generate antigen specific T and B cell receptor
- Failure to form functional T cell receptor complex (mutations in TCR signal transduction proteins)
- Abnormalities in stromal component of thymus
What are the features of SCID?
- Children: onset of disease less than 1 year, fatal if immune defect is not corrected with 2 years
- Multiple, recurrent opportunistic infections involving many organs
- Autosomal recessive or X-linked inheritance
- Complete penetrance
- Inherited from the parental genome
Describe the presentation of SCID?
- Unwell by 3 months of age
- Persistent viral, chest and GI infection (Para-influenza -3, adenovirus )
- Opportunistic infections (Pneumocystis jirovecii, CMV, )
- Live vaccine infection (BCG, rotavirus)
- Persistent or severe mucosal and/or skin candida infection
- Failure to thrive
- Unusual skin disease
- Graft versus host disease
- Bacterial infection rare
- Family history of early infant death
How is SCID diagnosed?
- Low lymphocyte count (counts are normally much higher in children than in adults
- CD3 T cell count < 300cells/uL
- T cell proliferation < 10% of control
- Low serum immunoglobulins
- Flow cytometry
- T- B+ SCID
- T-B-SCID
- Targeted gene panels
What is the management of SCID
- Stem cell transplantation
- HLA matched sibling
- HLA matched unrelated donor
- Haplo-identical donor
- Outcomes best
- Age less than 3.5 months
- No infection
- Matched sibling donor
- Survival from all donors equivalent of no infection present
- Early diagnosis improve outcomes
- No suitable donors: gene therapy
What is the role of gene therapy in SCID?
- Initial trials for X-Linked SCID led to restoration of T cell immunity but complicated by T cell leukaemia in 20% of recipients
- Development of safer viral vectors has reduced risk of T cell leukaemia
- Application of reduced conditioning to allow space in bone marrow for engraftment of gene transfected stem cell has allowed much better restoration of B cell function
What are some future directions in gene therapy for IEI?
- Application of gene therapy to other causes of IEI
- Gene therapy not a suitable option for a number of other PID (CGD, XLA)
- Use of use of gene editing in pre-clinical models to correct DNA defect using ZFN, TALENS and CRISPR/cas 9 technology
What is used to screen for SCID?
TREC analysis
How is TREC used for SCID screening?
- Generation of a T cell receptor is associated with formation of DNA extra-chromosomal ‘by-product’ called the T-cell receptor excision (TREC)
- Measurement of TREC in blood is a good biomarker of thymic function and can be used to identify low T cell counts in neonates
- Flow cytometry is then used to enumerate T cell counts in patients with low TREC counts and direct further investigation
- Results of TREC screen in the USA show
- SCID is more common than expected
- Improved outcomes following SCT
Outline some defects in T cell maturation/selection in thymus
DiGeorge syndrome -> thymic aplasia -> T cell deficient
What is DiGeorge syndrome (22q11.2 deletion syndrome)?
- Most common chromosomal deletion syndrome
- Occurs 1 in 1000 foetuses, 90% de novo deletions
- Developmental failure of pharyngeal arch (craniofacial structures, thymus, parathyroid glands aortic arch and cardiac outflow tract)
- Original description was clinical triad of immune deficiency hypoparathyroidism and congenital heart disease
- Now known to have heterogeneous presentation multiple additional congenital abnormalities (face, kidney), ENT, gastrointestinal, cognitive, behavioural and psychiatric features
How is DiGeorge syndrome diagnosed?
Chromosomal microarray
Outline DiGeorge syndrome and immune deficiency?
- 5% of children had reduced T cells number which usually resolve in early childhood
- Much smaller proportion of children present with SCID phenotype and thymic transplantation has emerged as a useful option
- Increased incidence of autoimmune disease (ITP) and humoral defects with age
Sino-pulmonary infection more often secondary to underlying structural upper airway disease with added subtle antibody defect (patient may benefit from antibiotic prophylaxis over winter)
What are secondary lymphoid tissues?
- Lymph nodes
- Spleen
- Mucosal lymphoid tissues
- Tonsils
- Adenoids
- Peyer’s patches
- Isolated lymphoid follicles
What are the functions of secondary lymphoid tissues/
- Site of T and B cell activation by APC
- Distinct functional subunits
- T cell area
- B cell area
- B cell area: germinal centres
- Positive selection for antigen specific B cells
- Some organs unique function
- Spleen removal aged red cells
What is selective IgA deficiency?
- Commonest primary antibody deficiency syndrome: incidence influenced by geography: 1 in 163 in Spain to 1: 14,840 in Japan
- Diagnosis: serum IgA less than 0.07g/L with normal serum immunoglobulins, vaccine responses and B and T cell counts
- 30% of individual are symptomatic
- Allergic disorders
- Sino-pulmonary and enteric infections
- Autoimmune disease (CD, ITP, SLE, AITD, and Type 1 DM)
- GI cancers
- Must be distinguished from IgA deficiency associated with IgG2 subclass and/or specific polysaccharide antibody deficiency
What is Common variable immune deficiency (CVID)?
Antibody deficiency syndrome characterised by
- Increased susceptibility to infection
- Autoimmune disease
- Granulomatous disease
- Lymphoproliferative disease
Describe CVID epidemiology?
- Commonest cause of primary antibody deficiency
- Prevalence 1 in 20,000 to 1 in 50,000 individuals
- Bimodal age for onset of symptoms
- 30% less than 10 years
- Adult onset: median age 35 years
- Average time between onset of symptoms and diagnosis is 5 years in the UK
Outline the CVID pathogenesis
- Heterogeneous group of conditions
- Defect in B cell function, characterised by failure to make protective antibodies to polysaccharide encapsulated pathogens
- Immune defect
- Intrinsic B cell defect in development, maturation or function
- Insufficient help from CD4 T cells
- Aetiology is largely unknown, polygenic disorder however in in a small proportion of patients (5-10%%) monogenic genetic mutation identified
What is the presentation of CVID (infections)?
- Recurrent bacterial sino-pulmonary infection with encapsulated bacteria such as Streptococcus pneumoniae and haemophilus influenzae type B
- Repeated chest and sinus may result in bronchiectasis, chronic sinusitis in 20-60% of patients
- Otiitis media and Haemophilus type b conjunctivitis
- Enteric infection with Campylobacter jejeuni and Giardia lamblia, small bowel bacteria overgrowth syndrome
- Skin: cellulitis, abscess, HSV and VZV infection
- Persistent, severe, recurrent respiratory viral (rhinovirus) and norovirus infections
- Normal life expectancy with IgG replacement therapy
CVID complex phenotype
- 20-30% of patients with CVID will experience an autoimmune/inflammatory disorder
- Autoimmune disorder in CVID patients (ITP, AIHA, thyroid disease)
- Autoinflammatory condition (CVID enteropathy, nodular regenerative hyperplasia and granulomatous hepatitis which can lead to portal hypertension and cirrhosis)
- Granulomatous interstitial lung disease: often with granulomatous infiltration in lymph nodes, spleen, skin, liver,
- Increased risks of B cell NHL and gastric cancer
- Monogenic CVID tend to more common associated with complex CVID phenotypes
- Reduced life expectancy: roughly 20% reduction over 20 years
How is CVID diagnosed?
- Age more than 4 years
- Reduction in serum IgG and IgA and/or IgM more than 2 SD below reference interval for healthy controls
- Poor vaccine responses to either carbohydrate (pneumovax) and/or protein antigen (tetanus)
- Exclusion of other causes of antibody deficiency (B Cell LPD and drugs induced syndromes)
What is the management of CVID?
- Standard management for complication of lung disease
- Physiotherapy
- Sputum surveillance
- Saline nebuliser and carbocysteine
- Standard antibiotic and airflow obstruction protocols
- Address co-morbidities (Sinus disease, GORD, OSA, Asthma)
- IgG replacement therapy
- Treatment of autoimmune and granulomatous complications of CVID
What is IgG replacement therapy?
- Only replaces IgG: not IgA and IgM
- Intravenous and subcutaneous preparations derived from plasma pools between 1,000 and 10,000 donors (European and from 2021 UK donors)
- IgG preparation will contain antibodies to pneumococcus, haemophilus tetanus, measles mumps and Hep A and Hep B
- Several different IgG products available
- All have similar efficacy
- Patient tolerability to different products vary
- ADR include fever, headache, myalgia, rash, rigors, anaphylaxis
- Supplies of different IgG products can be erratic
What is X-linked agammaglobulinaemia (XLA) [Bruton’s X-linked hypogammaglobulinaemia]? and what is it caused by?
- Presentation usually aged less than 5 years
- Mutation in BTK gene encoding Bruton Tyrosine Kinase
- Recurrent bacterial pyogenic infection involving ear, nose, throat, respiratory and gastrointestinal tract infection
- Microbiology: S. pneumoniae, H influenzae S aureus, and Pseudomonas spp:
- Virology: unique susceptibility to disseminated enteroviral infection if not on IgG replacement therapy
Defective B cell tyrosine kinase gene (BTK) -> Pre B cells cannot develop to mature B cells causing absence of mature B cells and no circulating Ig after ~ 3 months
- Recurrent infections during childhood
- Absent/scanty lymph nodes and tonsils (1° follicles and germinal centres absent)
What are some other features of XLA?
- Autoimmune and inflammatory disease not uncommon
- Usually absent all immunoglobulins isotype and marked reduction or absent B cells:
- Neutropenia can be a feature of XLA
- Family history of male relative on maternal side
- Standard management for bronchiectasis and chronic sinusitis with IgG replacement therapy
- Chronic or acute lung disease is the most common cause of death
Case 1 Current history: What investigations should be ordered?
39 year old female
Bronchiectasis associated with an unspecified ‘inflammatory bowel disorder’.
6-8 chest and 2-3 sinus infection a year for 3 years
Recurrent conjunctivitis over last 6 years
Shingles aged 31
Colonoscopy ‘Non specific colitis’ 2 years previously
Past medical history of psoriasis and hypothyroidism
Prominent family history of lymphoma, hypothyroidism, coeliac disease, pernicious anaemia and IgA deficiency affecting parents and siblings
Sputum cultures Pneumococcus and Haemophilus influenzae
FBC: Lymphocyte count 0.8 x109/L platelet count 105 x 109/L
IgG 3.8g/L IgA < 0.1g/L IgM 0.3g/L IgE < 0.5IU/ml
What are the variosu immunogolbuin level differences for various primary immune deficiencies?
Overall summary of primary immune deficiencies?
