Updated version of synoptic practice

INTRODUCTION

What is CTLA-4?

Inhibitory immune checkpoint protein

located on surface of T cells and Tregs

Negatively regulates T-cell activation

What is the main role of CTLA-4?

• acts as an immune brake

• suppresses excessive immune activation

• prevents autoimmunity

Maintain immune homeostasis

Why is CTLA-4 important?

• maintains self-tolerance

• regulates immune responses

• prevents chronic inflammation

What happens in CTLA-4 deficiency?

• excessive T-cell activation

• impaired inhibitory signalling

• immune dysregulation

• autoimmune disease

• recurrent infections

GENETICS

What inheritance pattern occurs in CTLA4 mutations?

• autosomal dominant inheritance

• mutation passes through generations

• one mutated gene copy contributes to disease

What is a heterozygous mutation?

• one normal CTLA4 gene copy

• one mutated CTLA4 gene copy

What is haploinsufficiency?

• one healthy gene copy is insufficient

• reduced CTLA-4 protein expression/function occurs

How does reduced CTLA-4 expression affect immunity?

• impaired inhibitory signalling

• immune dysregulation

• abnormal immune activation

What mutation types were identified?

• missense mutations

• nonsense mutations

• splice-site mutations

What are missense mutations?

• alter amino acids within CTLA-4 protein

• impair protein function

What are nonsense mutations?

• produce shortened proteins

• caused by premature stop codons

What are splice-site mutations?

• alter RNA processing

• impair protein expression

What is incomplete penetrance?

• some mutation carriers remain asymptomatic

• disease severity varies between individuals

How were CTLA4 mutations identified?

• pedigree analysis

• PCR amplification

• DNA sequencing

NORMAL FUNCTION OF CTLA-4

• suppress excessive immune activation

• maintain immune balance

• reduce T-cell activation

What is CD28?

• co-stimulatory receptor

• activates T cells

How does CD28 activate T cells?

• binds CD80/CD86 ligands

• promotes co-stimulatory signalling

How does CTLA-4 regulate CD28 activity?

• competes with CD28 for CD80/CD86 binding

• reduces co-stimulatory signalling

• suppresses excessive immune responses

How can impaired CTLA-4 increase inflammation?

• increased CD28-driven signalling

• increased inflammatory cytokine production

• chronic inflammation develops

Why is peripheral tolerance important?

• prevents immune cells attacking healthy tissues

• reduces autoimmunity risk

What are FOXP3-positive Tregs?

• specialised regulatory T cells

• maintain immune tolerance

• suppress excessive immune activation

What are Tregs?

• regulatory T cells

• suppress excessive immune responses

• maintain immune tolerance

Why is CTLA-4 important for Tregs?

• helps suppress activated T cells

• maintains immune regulation

What happened to Tregs in the paper?

• Treg numbers increased

• suppressive function impaired

Why is impaired Treg function harmful?

• excessive immune activation occurs

• chronic inflammation develops

• autoimmunity risk increases

Why is excessive T-cell activation dangerous?

• damages healthy tissues

• causes inflammation

• promotes autoimmune disease

What is autoimmune disease?

• immune system attacks healthy tissues

• caused by loss of immune tolerance

What is immune dysregulation?

• loss of proper immune control

• abnormal immune responses occur

How do CTLA4 mutations cause immune dysregulation?

CTLA4 mutation
→ reduced CTLA-4 function
→ impaired Treg suppression
→ excessive T-cell activation
→ chronic inflammation
→ autoimmunity + infections

What is transendocytosis?

• CTLA-4 removes CD80/CD86 molecules

• reduces immune activation

What is impaired ligand binding?

• CTLA-4 cannot effectively bind CD80/CD86

• inhibitory signalling decreases

How does CTLA-4 deficiency affect B cells?

• disrupts B-cell homeostasis

• reduces antibody production

• increases infection susceptibility

What CVID-like symptoms occurred?

• hypogammaglobulinaemia

• recurrent respiratory infections

CLINICAL MANIFESTATIONS

What is hypogammaglobulinaemia?

• low antibody levels in blood

• increased infection susceptibility

Why do recurrent infections occur?

• reduced B-cell numbers

• impaired antibody production

• immune dysregulation

What is lymphoproliferation?

• abnormal lymphocyte accumulation

• excessive immune-cell growth

What clinical manifestations occurred?

• recurrent infections

• autoimmune disease

• chronic inflammation

• lymphoproliferation

What organ complications occurred?

• granulomatous lung disease

• inflammatory tissue infiltration

• autoimmune enteropathy

• tissue damage

Why is excessive immune activation harmful?

• activated immune cells continue attacking tissues

• chronic inflammation causes organ damage

What is the purpose of analytical biochemistry?

• diagnose disease

• detect mutations

• analyse immune abnormalities

Why was PCR used?

• amplify CTLA4 DNA

• identify mutations

Why was DNA sequencing used?

• identify mutation types

• confirm genetic abnormalities

What is flow cytometry?

• measures optical/fluorescent properties of cells

• analyses immune-cell populations

Why was flow cytometry used?

• analyse Treg populations

• measure CTLA-4 expression

• identify immune abnormalities

What did flow cytometry demonstrate?

• impaired Treg suppressive function

• abnormal immune-cell populations

What characteristics does flow cytometry measure?

• cell size

• granularity

• fluorescence markers

What did MRI and CT scans demonstrate?

• inflammatory lesions

• tissue infiltration

• lymphoproliferative disease

What is the aim of therapy in CTLA-4 deficiency?

• suppress excessive immune activation

• reduce inflammation

• restore immune homeostasis

What is abatacept?

• CTLA-4-Ig fusion protein

• mimics CTLA-4 function

How does abatacept work?

• binds CD80/CD86

• reduces CD28 co-stimulation

• suppresses excessive T-cell activation

• restores inhibitory signalling

Why is abatacept targeted therapy?

• directly targets CTLA-4 pathway

• restores immune regulation

Why are corticosteroids used?

• reduce inflammation

• suppress excessive immune responses

Why is immunoglobulin replacement therapy used?

• replaces antibodies

• treats hypogammaglobulinaemia

• improves infection protection

What is the purpose of immunosuppressive therapy?

• control autoimmune disease

• reduce immune overactivation

What severe treatment may be used in some cases?

• haematopoietic stem cell transplantation

• restores immune function

CONCLUSION

What is the overall conclusion of the paper?

CTLA4 mutations impair inhibitory signalling leading to defective Treg function, excessive T-cell activation, immune dysregulation, chronic inflammation, autoimmune disease and recurrent infections. Genetics, immunology, molecular biology and analytical biochemistry are all integrated in understanding CTLA4-associated disease.