1. B Cell Development Kathleen E. Sullivan MD PhD Children’s Hospital of Philadelphia

2. Pro-B Pre-B1 Pre-B2 Immature B Mature B Plasma MHC II CD19 CD22 CD34 Ig  VpreB, 5 CD10 CD20 D-J VDJV-J light

3. Immature and Mature B cells Pre B cells must undergo positive selection of correct heavy chains expressed with VpreB and 5 Pre B cells must undergo positive selection of correct heavy chains expressed with VpreB and 5 Immature B cells exposed to antigen usually die (deletion of autoreactive B cells) Immature B cells exposed to antigen usually die (deletion of autoreactive B cells) Immature B cells develop into mature B cells in secondary lymphoid organs Immature B cells develop into mature B cells in secondary lymphoid organs Mature B cells exposed to antigen become activated Mature B cells exposed to antigen become activated

4. A few other ways to prevent autoreactivity Immature autoractive B cells can undergo receptor editing- “try again” Immature autoractive B cells can undergo receptor editing- “try again” Anergy: Seen with autoreactivity that is low affinity. Anergic B cells are excluded from the lymph node follicles and have a short life span Anergy: Seen with autoreactivity that is low affinity. Anergic B cells are excluded from the lymph node follicles and have a short life span Ignorance: Seen with weakly reactive B cells Ignorance: Seen with weakly reactive B cells

5. Germinal center development CD19 CD10 CD20 CD19 CD21CD22 CD20 CD22CD40CD38CD22 CD23sIgMCD77CD37 CD39CD40CD38 CD40Weak IgMCD40 CD76sIgM/A/G/E IgM/IgD Follicular B cellPrimary blastCentroblastCentrocyte Dark zone Light zone CD40:CD40L Somatic HM

6. Total B cells: CD19+ Total B cells: CD20+ Naive B cells: CD19+, IgD+, CD10+ (report triple +) Naive B cells: CD19+, IgD+, IgM+ (report triple +) Mature B cells: CD19+, CD20-, IgG+ (report as shown) Memory B cells: CD19+, CD27+, IgM+ (report triple +) Switched memory: CD19+, CD27+, IgM- ( as shown) B1 B cells: CD19+, CD5+ (report double +) HIGMII: CD19+, CD40+ (report double +) A few B cell markers used in flow cytometry