Gene conversion-like sequence transfers in a mouse antibody transgene: antigen selection allows sensitive detection of V region interactions based on homology.

Gene conversion is important for antibody diversification in chickens, rabbits and cows. In mice, however, conversion events appear to be infrequent among endogenous antibody genes. DNA sequence transfer events that resemble gene conversions have been reported for a mouse H chain transgene (VVC(mu)) that contains two closely spaced homologous VDJ segments. Surprisingly, these reported VVC(mu) sequence transfers were found frequently among mouse B cells responding to immunization. Transgene sequence transfers could be occurring at high frequency in responding VVC(mu) B cells or could be occurring at lower frequency with subsequent amplification by preferential antigen selection. To distinguish these possibilities, we have analyzed a second transgene (InVVC(mu)) that is identical to VVC(mu) except that the two VDJ regions have been exchanged in position. We find that transgene sequence transfers are much less frequent among responding B cells in InVVC(mu) mice, demonstrating the importance of selection in the frequent transgene conversions observed in VVC(mu) mice. These results suggest that mice, like other species, can use gene conversion to diversify antibodies. Such diversification events are apparently infrequent, however, and might only be detected among endogenous Ig genes with a favorable arrangement of V genes and an antigenic stimulation that selects cells with conversions. For both VVC(mu) and InVVC(mu) mice, conversion-like sequence transfers are strongly correlated with somatic hypermutation. Based on these results, we hypothesize that, in mice, gene conversions represent infrequent alternative reactions of a homology-based DNA repair process that is central in the somatic hypermutational mechanism.     

A B220(-), CD19(-) population of B cells in the peripheral blood of quasimonoclonal mice

We describe a new population of non-naive B cells in the peripheral blood of quasimonoclonal (QM) mice. Surface Ig of switched isotypes is expressed, but not B220 nor CD19. These cells are larger and denser than naive B cells but smaller than blasts or plasma cells; they do not stain with syndecan, a marker for plasma cells. Telomerase, which is usually expressed in B cell blasts, was not present in this population. We sorted the switched, idiotype-positive, B220(-) B cells from the peripheral blood of QM mice and sequenced Ig H chain and lambda L chain cDNA. There were many point mutations but no V gene replacements, gene conversions or other type of diversifications. As they express switched isotypes and have mutated their Ig genes, cells in the B220(-), CD19(-) population must have been in an immune response and we suggest that it includes the memory B cell subset.     

HPA polymorphism in sub-Saharan African populations: Beninese, Cameroonians, Congolese, and Pygmies

The frequency of human platelet antigen-1 (HPA-1) to HPA-11w (excluding HPA-8w) and HPA-15 systems was studied in four sub-Saharan populations: Beninese, Congolese (Democratic Republic of Congo Kinshasa), Cameroonians, and Aka pygmies (Central African Republic). No report of HPA prevalence has previously been published concerning these populations which are characterized by the highest HPA-2b gene frequencies of any reported to date (Aka 0.393, Benin 0.292, Cameroon 0.237, and Congo 0.224) and at lesser degree HPA-5b (Aka 0.405, Congo 0.268, Cameroon 0.254, and Benin 0.182). This study is of great importance (i) particularly in the context of the diversity caused by the population migrations, we may observe today in our hospitals (ii) to confirm that the Pygmy population with distinctive frequencies (absence of the HPA-1b, HPA-2b, and HPA-5b highest frequencies) is an isolated population.     

HLA-B27 polymorphism in Mumbai, Western India

Human leucocyte antigen (HLA)-B27 encompasses an increasing number of subtypes that show diverse racial/ethnic prevalence in the world. One thousand-one-hundred and seventy unrelated individuals from Mumbai, Maharashtra, Western India were typed for HLA-B27 antigen by serological methods. HLA-B27 positivity was confirmed by polymerase chain reaction using sequence specific primers. High-resolution typing using sequence specific primers for HLA-B27 alleles (B*2701 - B*2721) was carried out in 70 HLA-B27-positive individuals. The frequency of B27 ranged between 1.48 and 9.6% among the caste groups studied. HLA-B27 subtyping identified B*2702 (1.43%), B*2704 (14.29%), B*2705 (70%), B*2707 (12.86%) and B*2718 (1.43%), respectively. The findings illustrate substantial genetic variation and heterogeneity within population groups from India. Extensive subtyping in other Indian caste groups will be necessary to resolve the evolutionary implications of HLA-B27 subtypes and their relationship to disease association in the Indian context.     

V3 sequence analysis and biological characterization of HIV-1 isolates from asymptomatic and early symptomatic Tanzanian individuals

The aim of this study was to determine HIV-1 V3 sequences, in vitro biological characteristics and co-receptor usage of virus isolates from Tanzania. Virus was isolated from 14 of 17 samples investigated. Four of the isolates induced syncytia in MT-2 cells and used the CXCR4 co-receptor, while the remaining 10 isolates used the CCR5 co-receptor characteristic of non-MT-2 tropic viruses. One of the four MT-2 tropic isolates also used the CCR5 and CCR3 co-receptors. Proviral DNA was detected in all 14 isolates and PCR products were subjected to DNA sequencing. Unambiguous V3 amino acid sequences were obtained from 11 amplificates. Phylogenetic analysis indicated that these sequences were divergent and clustered in HIV-1 subtypes A, C or D. Sequences from the viruses that induced syncytia in MT-2 cells presented characteristic V3 phenotype-associated amino acids. Results of co-receptor analysis are in concordance with the isolate phenotype as determined by replication and induction of syncytia in MT-2 cells. The considerable diversity illustrated by a limited number of isolates from Tanzania is in accordance with reports from other regions of Africa.     

Diversity of Hepatitis G Virus within a Single Infected Individual

The extent of population diversity among GB virus C (GBV-C)/hepatitis G virus (HGV) within a persistently infected individual (Iw) was investigated by sequence analysis of multiple clones generated from polymerase chain reaction (PCR)-amplified products of cDNA analogous to fragments of 5 non-coding region (5NC), envelope region 1/2 (E1/E2) and non-structural region 3 (NS3) of viral genome. Although nucleotide substitutions were more common in coding regions than in the 5NC region, there was no region corresponding to the hypervariable region of hepatitis C virus in the E1/E2 region. Transition substitution exceeded transversion by 7 to 12-fold, and 79.4% of substitutions were synonymous. This bias against substitutions producing amino acid replacements and the use of Pfu DNA polymerase with an error rate 10 times lower than the observed frequency of substitution, suggests that most substitutions were not artefactual. This data suggests that individual genomes of HGV within an infected individual may differ from each other at 0.23–0.84% nucleotide position and at 0.42–0.61% amino acid position.     

Forensic characteristics and phylogenetic analysis of 23 Y-STR loci in the Miao population from Guizhou province,southwest China

Background: Investigation of haplotype/allele frequency data of Y-STR loci in ethnically diverse populations is essential for forensic reference database construction and genetic application. However, the population genetic characteristics of the Chinese Miao minority from Guizhou Province remain uncharacterised.

Aim: To assess forensic characteristics for 23 Y-Chromosomal STR loci in Guizhou Miao and explore population genetic relationships with geographically neighbouring populations.

Subjects and methods: Twenty-three Y-Chromosomal STRs were genotyped using the Powerplex^® Y23 system in 103 unrelated Chinese Miao males from Guizhou Province, southwest China. Haplotypes and forensic parameters were obtained. Population relationships of Guizhou Miao with others were revealed using AMOVA and an MDS plot.

Results: A total of 96 haplotypes were identified with overall haplotype diversity (HD) and discrimination capacity (DC) of 0.9985 and 0.9320, respectively. Genetic differentiation was observed with most of the comparison populations, prominently for Guizhou Shui.

Conclusion: The 23 Y-STR loci were highly polymorphic and discriminating in the Guizhou Miao population and could be used for forensic practice and population genetic studies. Population relationship analysis revealed Guizhou Miao had a close genetic relationship with geographically close Guizhou Gelao, as well as Han majorities derived from different regions.     

Optimal Household Water Access Fosters the Attainment of Minimum Dietary Diversity among Children Aged 6–23 Months in Malawi

Along with sanitation and hygiene, water is a well-known driver of child undernutrition. However, a more direct role of household (HH) water access in shaping dietary diversity remains unexplored. We assessed the association between HH water access and achievement of minimum dietary diversity (MDD) among young children. We utilized nationally-representative cross-sectional data from the 2015/16 Malawi Demographic and Health Survey, which included 4727 mother–child dyads, respectively, (26.8 ± 6.8 years, range 15–49 years) and (13.9 ± 4.9 months, range 6–23 months). HH water access was categorized as (1) basic or no access, (2) intermediate, or (3) optimal. MDD was defined as feeding a child, during the previous day, at least four of the food groups defined by the World Health Organization. Only 27.7% of the children achieved MDD standards; most of the children who achieved MDD were from HHs with optimal water access (58.4%, p < 0.001). However, only 5.9% of the mother–child dyads were from HHs with optimal water access. After adjusting for covariates, children from HHs with optimal water access had higher odds of achieving MDD than those from HHs with basic or no water access (aOR = 1.74, CI = 1.24–2.46). Our results highlight the need to incorporate water-based strategies into national nutritional policies to increase dietary diversity among Malawian infants and young children.     

PCT与SDI比值对重症细菌性肺炎患者短期预后的预测价值

 目的 探讨血清降钙素原(PCT)与肺泡灌洗液辛普森菌群多样性指数(SDI)比值对重症监护病房(ICU)内细菌性肺炎患者短期预后的预测价值。方法 回顾性调查扬州大学附属医院ICU 2019年10月—2021年7月选择肺泡灌洗液宏基因组二代测序(mNGS)技术的56例细菌性肺炎患者病历资料,依据其入ICU 24 h内急性生理学与慢性健康状况评分Ⅱ(APACHE-Ⅱ)分为非危重症组21例和危重症组35例。以细菌性肺炎造成死亡为终点事件,记录28天转归,并将患者分为生存组38例和死亡组18例。对各组患者的SDI、PCT、C-反应蛋白(CRP)、PCT/SDI、CRP/SDI进行比较分析。结果 与非危重症组比较,危重症组患者血清PCT/SDI、PCT水平均升高,且呼吸机辅助通气时间更长,28天病死率更高(均P＜0.05);与存活组比较,死亡组患者SDI较低,PCT/SDI、PCT水平均较高(均P＜0.05);SDI与呼吸机辅助通气时间呈负相关(r值为-0.655,P＜0.001),PCT水平、PCT/SDI与呼吸机辅助通气时间呈正相关(r值分别为0.660、0.734,均P＜0.001)。受试者工作特征曲线(ROC曲线)显示,PCT/SDI预测患者28天死亡的ROC曲线下面积(AUC)为0.851,其次为PCT+SDI (0.845)、PCT (0.808)、SDI (0.785)、CRP/SDI (0.731),PCT/SDI的最佳截断值为11.56时预判患者28天死亡的灵敏度为89.5%,特异度为66.7%。Cox回归分析显示,PCT/SDI值高(HR=1.562,95%CI：1.271~1.920,P=0.031)、PCT水平高(HR=1.106,95%CI：1.021~1.198,P=0.024)是ICU细菌性肺炎患者死亡的独立危险因素。结论 PCT/SDI、PCT、PCT+SDI、SDI、CRP/SDI均可作为ICU细菌性肺炎患者短期预后的评估指标。与其他指标相比,PCT/SDI预测患者短期预后更有价值。