Selective suppression of the murine autologous mixed lymphocyte reaction by physiological concentrations of hydrocortisone: effects on cell-surface Ia antigens

Strong, adult (Type II) autologous mixed lymphocyte reactions (AMLR) were observed in cultures of lymphoid cells from both A.TH and A.TL mice. These were suppressed by more than 90% in the continuous presence of 7.5 × 10^?8M hydrocortisone-21-sodium succinate. This concentration of hormone had minimal effects on the allogeneic mixed lymphocyte response (MLR) and the mitogenic response to concanavalin A (Con A). Higher concentrations suppressed all three responses. Treatment of autologous cell mixtures for the first 30 hr with 7.5 × 10^?8M hydrocortisone resulted in a 78% suppression of the AMLR. This was not associated with a detectable decrease in the quantity of Ia antigens on the stimulator-cell surface, as evaluated by the susceptibility of treated cells to antibody dependent, complement-mediated lysis, using [A.TH × B.10M]F₁ anti-A.TL antiserum. Hence, this suppression did not appear to result from an alteration of the antigens putatively associated with stimulation of the AMLR. Separate pretreatment of stimulator and responder cells with 7.5 × 10^?8M hydrocortisone followed by culturing with appropriate companion cells had no major effect on the AMLR. Therefore, low-dose hydrocortisone did not appear to selectively eliminate or permanently inactivate subpopulations of responder or stimulator cells. Rather, it appeared to regulate active cellular processes that are initiated by the coculturing of these cells and are required for the early stages of autologous lymphocyte activation.     

Effects of abscisic acid on CAM in Portulacaria afra

Water stress induces Crassulacean acid metabolism (CAM) in Portulacaria afra as manifested by day stomatal closure, organic acid fluctuation, and night CO₂ uptake. We now have evidence that abscisic acid treatment of leaves causes partial stomatal closure that is accompanied by the induction of CAM in a manner similar to water stress. There appears to be an inverse relationship between exogenous CO₂ uptake and decarboxylation of organic acids in that organic acids remain high during the day providing stomata are open. When stomata close, there is consumption of organic acids by decarboxylation. The hypothesis is that stomatal opening controls CAM in this species.This material is based upon work supported by the Science and Education Administration of the USDA under Competitive Grant No. 5901-0410-8-0018-0.     

Nitrogen fixation, denitrification, and pleomorphic growth in a highly pigmented Spirillum lipoferum.

A strain of Spirillum lipoferum with intense red pigmentation was isolated from the roots of Cynodon dactylon "Coastal." This isolate vigorously reduced acetylene when grown in N-free, Na-malate, semisolid agar, and it was identical to S. lipoferum strain SP7 by standard taxonomic tests. Both S. lipoferum SP7 and the C. dactylon root isolate displayed the unique features of being denitrifiers as well as N2 fixers. The N2-dependent growth curve was biphasic: cells in younger cultures showed the characteristic spiral shape and motility, but those in older cultures developed larger, nonmotile, cystlike forms. Nitrogenase activity seemed associated only with younger spiral forms. The red pigment may be a b- or c-type cytochrome. The strong red color, which this strain develops, could be used as a marker in evaluating soil inoculation experiments.     

Studies of the mechanisms for the induction of in vivo tumor immunity. VI. Induction of specific and nonspecific cell-mediated immunity in tumor-bearing hosts and its correlation with transplantation tumor immunity

Studies were performed to determine the development of cell-mediated cytotoxic response at tumor site in C57BL/6 mice bearing progressively growing FBL-3 ascites leukemia. The effectors isolated from tumor ascites are found to be highly cytotoxic for leukemic target cells. The levels of cytotoxicity obtained with effectors isolated from tumor site are generally higher than those obtained with immune mice. This cytotoxicity is both specific and nonspecific. The specific cytotoxicity against tumor-associated antigen is mainly mediated by T cells and the nonspecific cytotoxicity against unrelated tumor cells is mediated largely by macrophages. The T-cell-enriched preparation did not give significant natural killer activity. When testing the ability of these effectors to produce in vivo immunity against the challenge of FBL-3, it was found that only T cells could confer the transplantation-type immunity, but the immunity was transient. The macrophage-enriched preparation isolated from tumor ascites failed to give in vivo protection. These findings indicate that in FBL-3 system, mice with progressively growing tumors are able to develop immune response against tumor cells. However, this immunity is probably interfered with by a suppressor factor(s) or suppressor cells which restrict their activity to eliminate the tumor cells effectively.     

畜禽遗传资源冷冻保存中的取样方法探讨

本文基于遗传学和数理统计原理,提出了运用冷冻生殖细胞的方法长期保存畜禽遗传资源时,冷冻生殖细胞的4种取样方法,并推证了其误差公式和最低保存数量的估计公式。最后通过实例对公式的实际应用作了说明和讨论分析。     

黄腐酸增强小麦抗旱能力的生理生化机制初探

叶面喷施黄腐酸可显著提高小麦幼苗的保水能力,表现为降低叶面蒸腾强度,增加气孔扩散阻力,提高幼苗的生物量,在干旱条件下尤为明显。喷施黄腐酸可使干旱条件下叶片内脯氨酸含量提高近一倍,并在水分充足时,也能使叶片脯氨酸含量增加78%。     

我国汉族人群的乙二醛酶Ⅰ遗传多态性

用琼脂糖平板凝胶电泳技术分析了我国六个城市的汉族共1238人的红细胞乙二醛酶I的遗传多态性。每个汉族人群的受检人数和GLO1*1基因频率分别为:郑州200人(0.1023),哈尔滨195人(0.1103),呼和浩特210人(0.1259),贵阳204人(0.1373),兰州210人(0.1476),西安199人(0.1508)。中国不同地区汉族人群之间的GLOI基因频率分布存在显著性差异,但这种差异明显小于中国不同少数民族之间的差异。     

应用地理信息系统模拟森林景观动态的研究

根据地理信息系统的结构,通过数据文件的转换,把它与森林动态模型有机地结合起来,可实现对森林景观动态的模拟和预测。这种模拟方法的数据输入灵活,运行速度快,尤其是它可以获得一些以各种图表的形式输出的模拟结果。本文用文字和框图详细描述了地理信息系统的组成与结构,及森林动态模型的选择与运行方式,并以长白山森林景观为例,叙述了这种模拟方法的整个过程。