Switch region content of hybridomas: the two spleen cell Igh loci tend to rearrange to the same isotype

We have examined the switch region content of 25 hybridomas that secret antibodies of various isotypes with specificity for phosphocholine or glycoproteins of herpes simplex virus. These Southern hybridization experiments included probes for the murine JH region as well as probes for the mu, gamma 3, gamma 1, gamma 2b, gamma 2a, and alpha switch regions. For 22 of the hybridomas, the deletion model of the heavy chain switch fits the data well--all switch regions upstream of the rearranged (and expressed) switch regions are deleted and all switch regions downstream remain in the germline configuration. As exceptions to a simple deletion model of the switch recombination, we have observed two, and perhaps three, examples of switch region rearrangements downstream of an expressed heavy chain gene. The 25 hybridoma DNA samples include 28 rearranged gamma switch regions; the sizes of at least 25 of these rearranged fragments are consistent with recombination in the tandemly repeated sequences associated with gamma genes. For those hybridomas with two spleen cell-derived Igh loci, including three mu-expressers, three gamma 3-expressers, four gamma 1-expressers, and one gamma 2b-expresser, the two loci tend to be rearranged to the same switch region, suggesting that the heavy chain switch rearrangement is an isotype-specific event. The exceptions within this group include three hybridomas in which the switch seems to be incomplete--on one chromosome the JH complex is rearranged to the S gamma 3 region, while on the other it remains associated with the S mu region. A second group of hybridomas, which includes four gamma 3-expressers, have both gamma 3 and gamma 1 switch rearrangements. Each of these four hybridomas includes three rearranged JH segments, suggesting that they may be the result of an unusual differentiative pathway or a technical artifact. These experiments suggest that the heavy chain switch rearrangement in normal spleen cells is a deletion event that occurs within tandemly repeated elements. The rearrangement is mediated by factors with partial, or perhaps complete, isotype specificity.     

Mutations, duplication, and deletion of recombined switch regions suggest a role for DNA replication in the immunoglobulin heavy-chain switch.

The heavy-chain switch from immunoglobulin M (IgM) expression to IgA expression is mediated by a recombination event between segments of DNA called switch regions. The switch regions lie two to six kilobases upstream of the mu and alpha constant region coding segments. Switch recombination to IgA expression results in a recombinant mu-alpha switch region upstream of the expressed alpha constant region gene. We have characterized the products of switch recombination by a lymphoma cell line, I.29. Two sets of molecular clones represent the expected products of simple mu to alpha switches. Five members of a third set of molecular clones share the same recombination site in both the mu and the alpha switch regions, implying that the five molecular clones were derived from a single switch recombination event. Surprisingly, the five clones fall into two sets of sequences, which differ from each other by several point mutations and small deletions. Duplication of switch region sequences are also found in these five molecular clones. An explanation for these data is that switch recombination involves DNA synthesis, which results in nucleotide substitutions, small deletions, and duplications.     

Isolation of foamy virus from rhesus, African green and cynomolgus monkey Leukocytes.

Foamy virus (FV) was recovered regularly from the leukocyte of rhesus and cynomolgus monkeys and somewhat less often from African green monkey leukocytes. Virus was found in virtually all organs of experimentally infected rhesus monkeys. No illness or pathologic abnormalities were noted in these animals or in any of the naturally infected animals in spite of the prolonged period of viral persistence in various organs and tissues.     

鼠李糖乳杆菌LV108及其发酵乳免疫调节作用的比较

目的探讨鼠李糖乳杆菌LV108及其发酵乳对免疫抑制小鼠免疫功能的调节作用。方法将BALB/c小鼠随机分为5组,每组10只,即空白组(正常小鼠)、模型组(免疫抑制小鼠)、药物组(免疫抑制小鼠食物中添加左旋咪唑)、LV108菌悬液组(免疫抑制小鼠食物中添加LV108菌悬液)和LV108发酵乳组(免疫抑制小鼠食物中添加LV108发酵乳),除空白组外其余组构建免疫抑制小鼠模型。干预4周后,分别测定各组小鼠体质量和脏器指数,血清中白细胞介素2(IL2)、肿瘤坏死因子α(TNFα)和免疫球蛋白G(IgG)含量,血清溶血素含量、耳肿胀度和肝、脾巨噬细胞吞噬能力。结果相比模型组,LV108菌悬液组和LV108发酵乳组小鼠体质量增长速度、脏器指数、血清IL2与IgG水平、血清溶血值、耳肿胀度和巨噬细胞吞噬能力显著升高(均P<0.05);在脾脏指数、血清IL2与TNFα水平、血清溶血素含量和耳肿胀度免疫指标上,LV108菌悬液组与LV108发酵乳组之间比较差异具有统计学意义(均P<0.05)。结论LV108菌体及发酵乳对免疫抑制小鼠具备较全面的免疫调节作用,均可提高小鼠的自身免疫力;LV108发酵乳对小鼠的免疫调节作用强于LV108菌体。     

中国环境管理分区:方法与方案

我国生态环境可持续性及其影响因素的区域差异显著,各地区环境管理面临的主要挑战和需要优先解决的生态环境问题不同。进行环境管理分区,根据各地区生态环境特征及其影响因素的差异性,制定有针对性的环境管理政策,将有效促进我国区域生态环境的整体优化。采取定性和定量分析相结合的方法进行我国环境管理分区。首先,在我国3大自然区的基础上,根据我国的自然地理格局和已有的相关区划成果,把我国划分为4个环境管理大区,包括:南部季风区、北部季风区、西北干旱区和青藏高寒区。其次,通过建立的包含13个指标的环境管理分区指标体系,采用一维化欧式距离法分析各环境管理大区下相邻省级行政区环境特征的相似性,把环境特征相似性大的相邻地区划分到同一分区,得到以省级行政区为基本单元的我国环境管理分区方案。然后,结合地区间历史渊源和区域未来发展趋势分析,对基于相似性分析的初步分区方案进行调整,把我国划分为8个以省级行政区为基本单元环境管理区。最后,根据相关调整原则和方法,对以省级行政区为基本单元的分区方案的边界线进行调整,得到以地级行政区为基本单元的分区方案,把我国划分为东北地区、华北平原区、华北山地与高原区、东南沿海地区、长江流域中游地区、西南地区、西北干旱区和青藏高寒区8个环境管理区。     

DNA sequence of the murine gamma 1 switch segment reveals novel structural elements

Immunoglobulin heavy chain switch regions are segments of DNA considered to be important in mediating class switching in B lymphocytes. Whereas these segments vary in length among the different murine isotypes, their structural organization schemes are all based on the tandem repetition of unit sequences. We previously showed that the S gamma 1 segment unexpectedly contains sequence elements that differ significantly from its prevalent unit repeat (49mer). Here we extend this preliminary characterization by determining the complete nucleotide sequence of the cloned S gamma 1 segment from BALB/c DNA. We find that S gamma 1 consists of more than 120 tandemly repeated 49mers. In addition, we show that the previously identified non-49mer sequences are part of a direct repeat element about 350 bp in length (DR II), which exists in two copies at the 5' end of S gamma 1. We also show that another unrelated direct repeat element about 500 bp long (DR I) exists near the 5' and 3' ends of S gamma 1. Thus, the structure of the S gamma 1 segment might be may be abbreviated as 5'-DRII-(49mer)15-DRI-DRII-(49mer)n-DRI , where n is between 40 and 160. Our results of Southern hybridization experiments suggest that this basic structural scheme is maintained in eight different Igh haplotypes, although S gamma 1 segments in different Igh haplotypes include different numbers of 49mer elements. Other murine S gamma segments differ in size among various Igh loci, but to a lesser extent than S gamma 1. At the level of tandemly repeated sequences, S gamma 1, S gamma 3, and S gamma 2b represent three distinct, nonoverlapping sets of sequences.     

The immunoglobulin heavy chain switch: structural features of gamma 1 recombinant switch regions

The immunoglobulin heavy chain isotype switch is mediated by a DNA rearrangement involving specific genomic segments referred to as switch regions. Switch regions are composed of tandemly repeated simple sequences. The role of the tandemly repeated structure of switch regions in the switch recombination process is not understood. We mapped eight recombination sites--six in the gamma 1 and two in the gamma 3 tandem arrays. In addition, we obtained molecular clones representing three of the six gamma 1 rearrangements, and determined the nucleotide sequences of the recombination sites in each. In general, the rearrangements are confined to the tandem repeat units, and are not clustered in a particular portion of either the gamma 3 or gamma 1 switch region. Nucleotide sequence analysis of one of the recombinant clones, gamma M35, reveals evidence for a successive switch event wherein a recombination between S mu and S gamma 3 was followed by recombination 57 bp downstream with S gamma 1. gamma 1 sequence data from the molecular clones we obtained, together with similar data from other investigators regarding the gamma 1, gamma 2b, and gamma 2a switch regions, reveals that recombinations tend to occur at homologous positions of the respective gamma-unit repeats, adjacent to the elements AGCT and GGGG found in each. This finding suggests that the cutting and religation step of the recombination process is mediated by a recombinase common to the four gamma-isotypes.     

Lipid vesicle interaction with EMT-6 tumor cells and effect on subsequent cell growth

Artificial lipid vesicles of varying composition were incubated with EMT-6 tumor cells, after which the transfer of vesicle lipids to the cells and their growth $\text{in}\text{vitro}$ were determined. Vesicles composed of phosphatidylcholine, cholesterol, and gangliosides could transfer phosphatidylcholine and cholesterol to the cells, but this transfer had no effect on the subsequent growth of the cells. However, preincubation of the cells with vesicles containing sterylamine or phosphatidylserine did inhibit the subsequent growth of the cells in a tissue culture assay system. It might be possible to deliver to certain cells growth inhibitory compounds carried in lipid vesicles.     

Correlation of Bacterial Lipid Composition with Antibiotic Resistance

The correlation of bacterial lipid composition with antibiotic resistance was investigated with particular emphasis on those organisms in which resistance may be related to membrane or envelope structure or function, as in resistance to tetracyclines and polymyxin. Chloroform-methanol-extractable lipids, phosphatidyl ethanolamine fractions, and both fatty acids of these lipid fractions and total fatty acids were studied by using thin-layer chromatography, gas chromatography, and infrared spectroscopy. Consistent quantitative differences were found between the fatty acid compositions of sensitive and resistant strains. Most notable was the fact that, in gram-negative organisms, resistant strains showed decreases in cyclopropane acids as compared with sensitive strains. These changes were found to be inherent in the strains and not due to growth stage or culture age. No significant qualitative differences were noted. In contrast, no such variation in fatty acid content was observed in penicillin-sensitive and resistant strains of gram-positive cocci. As significant alterations of fatty acid composition were noted in gram-negative strains resistant to antibiotics, we suggest that resistance is correlated to membrane or envelope lipid composition.