Novel atypical nucleotide insertions specifically at V_H–D_H junction generate exceptionally long CDR3H in cattle antibodies

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• 作者：Madhuri Koti ; Galina Kataeva ; Azad Kumar Kaushik
• 关键词：CDR3H ; Antibody diversity ; Bovine D_H gene segment
• 刊名：Molecular Immunology
• 出版年：2010
• 出版时间：July 2010
• 年：2010
• 卷：47
• 期：11-12
• 页码：2119-2128
• 全文大小：2245 K

文摘

Some IgM cattle antibodies are amongst the largest known to exist in jawed vertebrates where CDR3H size may extend up to 61 amino acids. To understand the origin of such an exceptionally long CDR3H, bovine D_H gene locus was completely characterized from Holstein cattle that revealed the presence of a total of eight D_H genes, including D_HQ52, with a distinct organization in sub-clusters. However, a total of 10 D_H genes are identified at the polymorphic D-gene locus in cattle that are classified into four families, designated as BovD_HA, BovD_HB, BovD_HC and BovD_HD. In fetal B-cells, VDJ recombinations encoding long CDR3H (>50 codons) are directly encoded by the single germline V_H gl.110.20, the longest D_H2 and the J_H1 genes, apart from few N- and P-nucleotide additions at the junctions. Further, non J-proximal D_H7 gene is preferentially expressed in fetal B cells. The adult VDJ recombinations, however, are distinctly remarkable for ‘conserved short nucleotide sequence’ (‘CSNS’; 13–18 nucleotides), of non-V_H or D_H gene origin, inserted specifically at V_H–D_H junctions resulting in extension of CDR3H size up to 61 codons. Together with P-nucleotides, N-additions (1–9 nucleotides) are noted at both the V_H–D_H and D_H–J_H junctions. Such ‘CSNS’ insertions at V_H–D_H junction of adult VDJ recombinations encoding exceptionally long CDR3H provide novel mechanism of antibody diversification in cattle, not yet observed in other species. Further, analysis of V_H–D_H–J_H recombinations originating from fetal B-cells reveals the presence of substitution, deletion or addition mutations without prior exposure to external antigen. Thus, somatic hypermutations may contribute towards diversification of the developing nascent antibody repertoire in cattle. In conclusion, the outlined experiments provide novel antibody diversification mechanism via ‘CSNS’ insertions, specifically at the V_H–D_H junction, in generating exceptionally long CDR3H extending up to 61 codons in cattle antibodies.