A productively rearranged heavy chain is expressed immediately during proB-preB transition as a membrane pre-B receptor
Surrogate light chains (λ5 and VpreB)
-Expressed transiently : production of λ5 mRNA stops as soon as pre-B cell receptor formed -pre-B receptor signaling via accessory chains stops heavy chain rearrangement
-Induces proliferation
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-Large pre-B cells divide several times (expand 30X to 60X)
-Resting small pre-B cells
-RAG re-expressed for L chain rearrangement
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-Single pre-B cell can generate different antigen specificities (B cell diversity)