basic science of b cell disorders - allergy
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Basic science of B cell disorders
Stuart Tangye
Human B-cell development and differentiation
Human B-cell development and differentiationMutations compromising B cell development
- agammaglobulinemia• BTK (XLA)
• Ig µ, Igα, Igβ• λ5
• BLNK• E47, IKAROS
(• RAG1/2)X X X
X X X X
X X
Kinetics of the Humoral Immune Response
B-Cell Activation in Lymphoid Tissues
1. Initiation of 1˚ response in the T cell zone
“Extrafollicular reaction”
Short lived cells
Kinetics of the Humoral Immune Response
“Extrafollicular reaction”
B-Cell Activation in Lymphoid Tissues2. Maturation of the B cell response: “Germinal centre” reaction
Periph blood, 2˚ lymph tissues, BM
Bone Marrow
Dark Zone- centroblasts - SHM- intense proliferation
Light Zone- centrocytes- hi-affinity clones receive survival
signals, express survival genes- Recycle to DZ, or exit
Outer Zone- differentiation of hi-affinity centrocytes into memory B or plasma cells
De Silva & Klein (2015). Nat Rev Immunol 15: 137
Kinetics of the Humoral Immune Response
“GC reaction”
Why mutate Ig V region genes?
• allows immune system to select B cells expressing Ag receptors (ie Ig) with increased/improved affinity for the immunising Ag/pathogen
• generates highly Ag-specific immune response
• provided B cells with a survival advantage
• facilitates more rapid elimination of infectious pathogen
Why switch Ig isotypes?
• isotype switching provides secreted Ig with distinct biological activities
- IgG : longer t1/2 than IgM; : binds FcγR to increase phagocytosis: activates complement pathway/system
- IgA : produced predominantly in the mucosa: often 1st line of defence against pathogens: dimeric
- IgE : binds IgεR to activate mast cells, basophils: important in anti-helminth responses
• necessary for adaptive Ab responses
IgM IgD IgG IgA
CSR & SHM: AID-dependent processes
Delkeret al., 2010. Nat Immunol. 10: 1147
GC and memory formation are T-cell dependent
• nude mice (greatly deteriorated thymus)• thymectomised mice• anti-CD4 mAb treated mice• αβ TCR gene deficient mice
ALL UNABLE TO MOUNT LONG LIVED Ab RESPONSES
Control mice
Thymectomised mice
Ant
ibod
y re
spon
se
But which molecules, interactions and cells are required?
Role of CD40 During a B-Cell Response
Van Kooten & Banchereau (1996). Adv. Immunol. 61: 1-77
IL-21 IL-21
IL-21
IL-21
What would happen if the CD40/CD40L interaction was prevented?
x
Van Kooten & Banchereau (1996). Adv. Immunol. 61: 1-77
x
x
x
IL-21 IL-21
IL-21
IL-21
Hyper-IgM Syndrome (Ig class switch recombination deficiencies)
• ↑ or normal IgM • ↓ IgG ↓ IgA ↓ IgE • Ie impaired CSR; reduced SHM • Extremely susceptible to recurrent bacterial and
opportunistic infections – Pneumocystis carinii pneumonia, – cryptosporidium– CMV
• No germinal centers (ie TD immune responses) • Lack of humoral memory • X-lined and autosomal forms
X-lined Hyper-IgM Syndrome (HIGM-1)
• ~50% of all cases of HIGM (TRAP = CD40L)
Defective GC formation in HIGM1Control HIGM
H&E
Ki67
CD23 (FDCs)
Facchetti et al., 1995. J Immunol. 154: 6624
Autosomal recessive HIGM: HIGM3
Engagement of CD40 activates NFκB
Puel et al. 2004. Curr. Opin. Immunol. 16: 34
Lack of T-cell help
Unable to receive or transmit T-cell help
Durandy & Honjo (2001). Curr Opin Immunol 13: 543
• reduced IgM memory B cells, no switched memory B cells
Hyper-IgM Syndrome
B-cell intrinsic HIGM: mutations in mediators of CSR and SHM
B-cell intrinsic HIGM: HIGM2• ↑ or normal IgM • ↓ IgG ↓ IgA ↓ IgE • impaired CSR (± SHM) • Hyperplastic lymph nodes/germinal centers • Intact T cell function g not susceptible to opportunistic infections • Often not recognised til 2nd or 3rd decade of life
Revy et al (2000). Cell 102: 565
B-cell intrinsic HIGM: HIGM2• ↑ or normal IgM • ↓ IgG ↓ IgA ↓ IgE • Impaired CSR (± SHM) • Hyperplastic lymph nodes/germinal centers • Intact T cell function g not susceptible to opportunistic infections • Often not recognised til 2nd or 3rd decade of life
Clinical/immunologic features of HIGM syndromes
Notarangelo et al., 2006. J Allergy Clin Immunol. 117: 855
CD40L is predominantly expressed by CD4+ T cells in the outer zone of GC’s (Tfh cells)
Hutloff et al (1999). Nature. 397: 263
…..as is ICOS Casamayor-Palleja et al (1995). J Exp Med. 181: 1293
CD40L Ki67 CD4
Inducible Co-Stimulator (ICOS)
Schwartz (2001). Nature. 409: 31
4/36 CVID patients
IL-21R/γc/JAK3/STAT3 signalling is necessary for humoral immunity in vivo in humans
STAT3JAK3
T follicular helper (TFH) cells• CD4+ CXCR5hi T cells that localise to B-cell follicles/germinal centres• express high levels of many molecules involved in T/B interaction/regulation
• provide help to B cells via production of specific cytokines
Ma et al. 2009. Immunol Cell Biol. 87: 590
X-HIGM ICOS CVID XLP
Correlation between TFH and memory B cells
Intrinsic and extrinsic regulators of human B-cell differentiation
B-cell differentiation: the role of co-receptors
Rolink & Melchers (2002). Curr Opin Immunol. 14: 266
CD19: B-cell co-receptorOpsonised Ag - ligates 2 receptors
CD19-deficient patients
CD19-deficient patients
- 6 patients total
- 4 unrelated families; different homozygous mutations
- recurrent infection, hypogamma, impaired recall responses to vaccine Ags
- Memory B cell deficiency
- normal GC formation, reduced SHM
- reduced B cell responses in vitro
- (2 other unrelated CD19 mutant pts been reported; initially diagnosed as B-cell deficient due to lack of CD19+ cells!)
Another case of CD19 deficiency?
Another case of CD19 deficiency?
- phenocopy of CD19-deficiency
CD21 deficiency
- hypogamma ± recurrent infections, reduced memory B cells, reduced response to polysacch Ag; ± defective B cell responses in vitro
- not as severe as CD19-deficiency
Rolink & Melchers (2002). Curr Opin Immunol. 14: 266
- reduced switched memory B cells
- low serum IgG
- impaired responses to TI Ag (ie PneumoVax) but not TD Ag
B-cell differentiation: the role of co-receptors
Novel gene mutations underlying CVID and humoral immune defects
Novel gene mutations underlying CVID and humoral immune defects
NFKB2 (p100)
NFKB1 (p50)
B-cell differentiation: the role of co-receptors
Rolink & Melchers (2002). Curr Opin Immunol. 14: 266
Intrinsic and extrinsic regulators of human B-cell differentiation