Studies on chicken immunoglobulin gene moditication and attinity maturation

鸡法氏囊卵泡和生发中心由于其易于分离和免疫球蛋白基因的PCR扩增，使我们能够分析b细胞的法氏囊和法氏囊后分化。不依赖抗原的法氏囊b细胞通过基因转换和点突变多样化，在孵化前产生致残突变，产量高达50%，但在孵化后通过抗原依赖的正选择，致残突变率显著降低。在生发中心反应的早期阶段，迁移到单个生发中心的囊后b细胞通过基因转换进一步多样化，随后遭受点突变和寡克隆选择，这可能是亲和成熟的中间步骤。我们发现了两个开关区，即由TATGG和ACCAQ五聚体重复序列组成的长5kb的Smu区和TATGG和GGCAG重复序列组成的S γ区，并在这两个区域之间显示了缺失的开关重组。

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.