Development of the Immune System

Question 1

What’s the peak age of serious bacterial infections?

What’s it called when Neonates lack specific immune responses?

What is the Innate immune system? What does it consist of?

What is the Adaptive immune system? What does it consist of?

Answer 1

• <5yrs
• DEVELOPMENTAL IMMUNODEFICIENCY
• Non-Antigen Specific - Barriers (Skin, Mucosa), Cells (Neutrophils, Macrophages, Monocytes), and Soluble components (Complements, Cytokines)
• Antigen-Specific - T/B Lymphocytes and Specific antigens

Question 2

FOETAL DEVELOPMENT:
What’s the 1ST stage? What occurs here? How long does it last?

What’s the 2ND stage? How long does it last?

What’s the 3RD stage? When does it occur?

What’s the 4TH stage? What occurs here?

Answer 2

• MESOBLASTIC - Haematopoietic cells in the Yolk sac
  o Primitive nucleated RBCs from week 3
  o Lasts 10 weeks
• HEPATIC - From week 6-8 till birth
• SPLENIC - Transiently occurs before myeloid phase
• MYELOID - Initiates in bone marrow from week 10-12

Question 3

ANATOMY:
What are the Primary Lymphoid Organs? What does each do?

What are the Secondary Lymphoid Organs? What does each do?

Answer 3

• • THYMUS - T cells learn their job here (maturation)
  • BONE MARROW - Site of Haematopoiesis
• • SPLEEN - Filters blood; removes old/damaged RBCs, and infectious agents to activate lymphocytes
  • LYMPH NODES - Filters out dead cells, antigens and other materials to present to lymphocytes

Question 4

INNATE IMMUNITY (NON-ANTIGEN SPECIFIC):
What type of cells are involved?
→ When do they begin developing?
→ What are these cells like?

What are the Soluble components involved?

Answer 4

• Granulocytes (Neutrophils, Macrophages, Monocytes)
  → Week 31
  → High in number, but less effective
• • Complement - Serum proteins that function as an enzymatic cascade, Reduced function in children
  • Cytokines - Less produced by Dendritic cells

Question 5

ADAPTIVE IMMUNITY (ANTIGEN-SPECIFIC):
T Lymphocytes:
Where are they produced, and where do they go?

What do they present on their surface?

What embryological structure does the Thymus form from?
→ When is it fully formed by?

B Lymphocytes:
What are they produced from? Where do they then go?

What do they express on their surface?
→ How does this differ with Immature B cells?

Why is it important for Neonates to receive Ig’s? Where do they get it from?

What does Secretory IgA do?

Answer 5

• Bone marrow → Thymus for Maturation → Secondary Lymphoid organs
• Unique antigen receptors
• 3rd Pharyngeal pouch
  → Week 20

• Primitive stem cells in Bone marrow → Secondary Lymphoid organs
• Immunoglobulins (Ig) of single-antigen specificity
  → Has many different Ig molecules on its surface for antigen binding and clonal selection
• They’re deficient in their own-generated Ig’s - Gets Maternal IgG via placenta and Secretory IgA via breast milk
• Inhibits the adherence of bacteria to mucosal surfaces

Question 6

What are Newborns more susceptible to?

How can they be protected from these susceptibilities?

UK Vaccination Schedule:
What is given at birth?

Which vaccines are given from 2 months?

What is then given at 12 months?

Answer 6

• Severe bacterial and viral infections
• • Early treatment with antibiotics/antivirals
  • Limit exposure to infection e.g. handwashing, avoid unnecessary procedures
  • Encourage breastfeeding
  • Maternal vaccination
  • Infant vaccination

• BCG (1 dose)
• • Diphtheria/Tetanus/Pertussis/Haemophilus influenzae b/Polio need 3 doses at 2, 3, 4 months
  • S. Pneumoniae/Rotavirus/N. Meningitidis B need 2 doses at 2 and 4 months
• 1st MMR dose and Booster doses