Studies on chicken immunoglobulin gene moditication and attinity maturation

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Chicken bursal follicles and germinal centers enabled us to analyze the bursal and postbursal diversification of B-cells due to its easy isolation and the PCR amplification of immunoglobulin genes.Antigen-independent bursal B-cell diversification by gene conversions and point mutations generated crippling mutations at the high yield of 50% before hatching but the crippling mutation ratio was dramatically decreased by antigen-dependent positive selection after hatching.Postbursal B-cells migrating into single germinal centers are further diversified by gene conversion in the early phase of germinal center reaction and are subsequently subjected to point mutations and selection for oligoclonality which may represent an intermediate step of affinity maturation.We characterized two switch regions, Smu region of 5 kb long composed of TATGG and ACCAQ pentameric repeats and S gamma region of TATGG and GGCAG repeats and showed deletional switch recombinations between these two regions.