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In mammals and the amphibian, Xenopus, isotypes of antibodies have been shown to be changed through class switch recombination within the IgH chain gene locus. Here, we identified switch (S) repetitive sequences in the 5′ introns of the Ig C_μ and C_γ genes of the chicken. The S_μ region is composed of two homologous regions, S_μ1 and S_μ2. The S_μ1 region is an upstream 3.7 kb sequence composed of 37 repeats of a consensus sequence containing tandem repeats of the decamer ACCAGTATGG. The S_μ2 region is a downstream 1.4 kb sequence consisting of simple tandem repeats of a decamer CCCAGTACAG. The S_γ region contains repeats of the decamer TATGGGGCAG. Analysis of chicken IgG-producing hybridomas revealed that the C_μ gene was deleted from the chromosome by the recombination occurring between the S_μ and S_γ regions. Recombination breakpoints at the C_μ gene of splenocytes from an immunized chicken were scattered around the S_μ region and two such breakpoints, the precise position of which were determined, were located within possible hairpin loop structures at the palindromic sequence of S_μ1. A primordial palindromic sequence from which the prevalent switch repeat motifs of mammals, chickens and amphibians may have diverged is presented.

In mammals and the amphibian, Xenopus, isotypes of antibodies have been shown to be changed through class switch recombination within the IgH chain gene locus. Here, we identified switch (S) repetitive sequences in the 5' introns of the Ig C(mu) and C(gamma) genes of the chicken. The S(mu) region is composed of two homologous regions, S(mu)1 and S(mu)2. The S(mu)1 region is an upstream 3.7 kb sequence composed of 37 repeats of a consensus sequence containing tandem repeats of the decamer ACCAGTATGG. The S(mu)2 region is a downstream 1.4 kb sequence consisting of simple tandem repeats of a decamer CCCAGTACAG. The S(gamma) region contains repeats of the decamer TATGGGGCAG. Analysis of chicken IgG-producing hybridomas revealed that the C(mu) gene was deleted from the chromosome by the recombination occurring between the S(mu) and S(gamma) regions. Recombination breakpoints at the C(mu) gene of splenocytes from an immunized chicken were scattered around the S(mu) region and two such breakpoints, the precise position of which were determined, were located within possible hairpin loop structures at the palindromic sequence of S(mu)1. A primordial palindromic sequence from which the prevalent switch repeat motifs of mammals, chickens and amphibians may have diverged is presented.

It has been believed that the peripheral lymphocytes in chickens proliferate by self‐renewing amplification of the preimmune repertoire generated in bursa. We amplified rearranged immunoglobulin variable (V) region genes from the single germinal centers induced by immunization. The sequence analysis of these genes revealed that most were derived from distinct B‐cell clones which expanded locally, generating somatic antibody mutants at a high rate. Somatic hypermutations included unlinked base changes and the linked base modifications interpreted as unidirectional transfer of sequences from V region pseudogenes. This finding demonstrates the ongoing post‐bursal diversification of B‐cells in splenic germinal centers by templated gene conversion as well as untemplated point mutations.

It has been believed that the peripheral lymphocytes in chickens proliferate by self‐renewing amplification of the preimmune repertoire generated in bursa. We amplified rearranged immunoglobulin variable (V) region genes from the single germinal centers induced by immunization. The sequence analysis of these genes revealed that most were derived from distinct B‐cell clones which expanded locally, generating somatic antibody mutants at a high rate. Somatic hypermutations included unlinked base changes and the linked base modifications interpreted as unidirectional transfer of sequences from V region pseudogenes. This finding demonstrates the ongoing post‐bursal diversification of B‐cells in splenic germinal centers by templated gene conversion as well as untemplated point mutations.

SummaryWhen the bursa of Fabricius was isolated from environmental stimuli across the bursal epielium by clipping the bursal duct on the 19th day of incubation, marked retardation was observed both in the bursal development and in the maturation of the immune reactivity. Neither necrotic changes nor involution in the bursa was, however, observed at any stage examined after clipping the bursal duct. Lymphopoiesis in the bursa and the immune reactivity of these chickens gradually increased with age, although they were constantly lower than those of controls. These results suggest that environmental stimuli across the bursal epithelium play an important role in the amplification mechanisms for B-cell differentiation in the bursa.Australian Journal of Experimental Biology and Medical Science (1980) 58, 289–296; doi:10.1038/icb.1980.28

The first methylmercury poisoning by consumption of fish arose in Minamata, Japan, in 1953. Methylmercury dispersed from Minamata to the Shiranui Sea until 1968. Mercury concentration in the hair of residents on the coast of the Shiranui Sea was 10 to 20 times higher than that in nonpolluted people in Kumamoto Prefecture in 1960. People on the coast of the Shiranui Sea have consumed fish containing low-dose methylmercury without a ban over decades until 1968. We studied the effect of long-term consumption of methylmercury on those people 10 years later after the end of methylmercury dispersion. Our epidemiological study clarified that people in a fishing village (Ooura) on the coast of the Shiranui Sea showed a significantly higher frequency of neurological signs characteristic of methylmercury poisoning (hypoesthesia, ataxia, impairment of hearing, visual change, and dysarthria) in comparison with people in a nonpolluted fishing village (Ichiburi), The neurological disorders mere still detected 10 years later in Ooura after the end of methylmercury dispersion from Minamata; hypoesthesia showed the highest frequency in Ooura, These results suggest that people on the coast of the Shiranui Sea were affected by long-term dietary exposure to methylmercury.