Activation of rat B lymphocytes. II. Functional and structural changes in "aged" rat B lymphocytes

Anti-mu, anti-gamma, and anti-delta antibodies induce proliferation of splenic B lymphocytes from young Lewis rats, measured by 3H-TdR uptake. In contrast, splenic B cells of aged Lewis rats respond poorly or not at all to these reagents. T lymphocytes or interleukin 2 (IL-2) of young or aged rats augment the uptake of 3H-TdR in cultures of "young" B cells responding to anti-Ig reagents or LPS and DxS, but have no significant effect on the responses of "old" B cells. Analysis of spleen cells of young and aged rats in a fluorescence-activated cell sorter indicates the density of mu, gamma, and delta isotypes is reduced in "old" B cells, and that B cells of aged rats are significantly larger than those of young rats. These results delineate anatomic and structural changes in B lymphocytes of aged rats.     

Antigen-initiated B lymphocyte differentiation. XIV. Nonspecific effects of antigen stimulation cause proliferation in the "pre-progenitor" subset of primary B cells.

The effect of specific and nonspecific stimuli on the cycle status of subsets of primary B lymphocytes was assessed by preinjecting donor CBA mice 1 to 2 days previously with various substances, and then incubating the isolated spleen cells with high specific activity 3H-TdR before assay. AFC-progenitor activity was assessed as a response to NIP-POL antigen, either by adoptive transfer to irradiated recipients or by cell culture. Previous studies showed these assays reflected the activity of different subsets of B cells, termed "pre-progenitors" (adoptive assay) and "direct progenitors" (culture assay). Most functional primary B cells, whether assayed in culture or by adoptive transfer, were not initially in rapid cell cycle in normal adult mice. However, nonspecific stimulation for 1 day caused NIP-specific adoptive transfer IgM AFC-progenitors to enter rapid cell cycle. This effect was independent of T cells and not related to the antigenicity of the stimulus: particulate peritoneal irritants were the most effective stimulants. In contrast to adoptive transfer results. AFC-progenitors assayed in cell culture were unaffected by nonspecific stimuli, but were activated into cell cycle by specific antigen.     

新型冠状病毒南非B.1.351变异株的分离与分子特征分析

2020年12月广州市第八人民医院收治了 1例南非输入性COVID-19病例,经检测为SARS-CoV-2核酸阳性的实验室确诊病例.本研究使用Vero-E6细胞,对该病例咽拭子样本进行病毒分离,逐日观察,咽拭子接种的细胞管3d开始出现细胞融合样细胞病变(Cytopathic effect,CPE),5d出现完全CPE后再进行第二代接种,2d出现病变,提取核酸进行鉴定,为SARS-CoV-2阳性.第2代复传的SARS-CoV-2病毒株TCID50测定结果为5.5log TCID50/0.1mL～5.8log TCID50/0.1mL.对分离毒株经采用三代测序成功获得全基因组序列,进化分析结果为与参考毒株Wuhan/Hu-1/2019相比共发生30个碱基的变异、18个氨基酸的突变和18个碱基的缺失,比对结果显示分离到的毒株为SARS-CoV-2南非B.1.351变异株.     

A "Reverse burst" active site titration procedure for human carbonic anhydrase B.

Between pH 7 and pH 10.5, p-nitrophenyl $\text{p}$-sulfamyl benzoate (PNP-SAB) binds very strongly to human carbonic anhydrase B (dissociation constant on the order of 10^?9 M or less at pH 7.5), but is not hydrolyzed by the enzyme. Because the binding is essentially stoichiometric under readily accessible conditions, this ester may be used as an active site titrant, by measuring the rapid hydrolysis of excess unbound PNP-SAB catalyzed by an added nucleophile (“reverse burst”).     

RAPD早期鉴定平邑甜茶与B9的杂交群体

应用RAPD技术寻找平邑甜茶与B9的差异引物,用于早期筛选以平邑甜茶为母本B9为父本的杂交群体。在用于筛选的72个引物中找到符合要求的4个随机引物共7个特异位点,用这4个随机引物筛选杂交群体的25株个体,鉴定出5个杂交个体：307、308、319、322、324。     

Cell differentiation in the presence of cytochalasin B: studies on the "switch" to IgG secretion after polyclonal B cell activation.

Mouse spleen cells were cultured with lipopolysaccharide in conditions that activate both IgM and IgG secretion. Addition of cytochalasin B (CB), an inhibitor of cytokinesis, lead to a high degree of polynucleation, with little effect on Ig secretion. Using cytoplasmic staining with fluorochrome conjugated antisera, we determined the numbers of IgG-containing cells that also contained IgM in their cytoplasm. Such double staining cells were relatively more frequent at early times of the cultures, but at all times single producing cells were in the majority. Addition of CB over the period when the IgG producing cells first appear, lead to a marked increased frequency of double staining, polynucleated cells. This characteristic was stable over a period of at least 42 hr, suggesting that each double staining cell actively synthesized both isotypes. When CB was added after IgG production had started, little increase in the numbers of double staining cells were observed, although polynucleation remained extensive. These data confirm previous findings that the lineage of one cell can produce both IgM and IgG. Furthermore, the results suggest that cells in the process of switching from IgM to IgG go through an asymmetric division leading to one IgM-producing and one IgG-producing daughter cell.