Heme/Immunology primer

• gestation 1 week: blood islets appear in yolk sac
• 4 weeks: more blood islets (these are pluripotent cells)
• 6-7 weeks: cells migrate to fetal liver for hematopoesis, and to a secondary site in the spleen
• 13 weeks: further migration to BM, thymus (t-cells); B cells are thought to differentiate in the BM. Prior to this, cells are pluripotent, naïve, non-educated lymphoid cells that are not immunocompetent. Hence, before 13 weeks, foreign antigens aren’t identified/destroyed.
• 22 weeks: by this time, there aren’t many hematopoetic cells left in liver

Host Defenses

Innate immunity is Non-specific

• Structural barriers (skin and its secretions)
• Phagocytes
• Complement

Adaptive immunity is antigen specific

• B-cell (humoral)
• T-cell (cell mediated)

Disorders of Phagocyte dysfunction (innate immunity)

1. Disorders of chemotaxis: Hyper IgE Syndrome
2. Adhesion Abnormalities: Leukocyte Adhesion Deficiency
3. Degranulation Abnormalities: Chediak-Higashi syndrome
4. Defects of Microbial Activity : Chronic granulomatous disease

Complement defects (innate immunity)

1. Initial defects: Association with autoimmune disorders
2. Terminal defects: Increased risk of infection
3. C1 Esterase Inhibitor