Suppressive effect of human natural killer cells on pokeweed mitogen-induced B cell differentiation

The suppressive effect of human natural killer (NK) cells on B cell differentiation induced by pokeweed mitogen (PWM) was investigated. By using Percoll discontinuous density gradient centrifugation, peripheral blood nonphagocytic and nonadherent mononuclear cells were divided into low and high density fractions for which NK cells (Large granular lymphocytes, LGL) and T cells were enriched, respectively. These fractionated mononuclear cells were co-cultured with purified autologous B cells in the presence of PWM, and were examined for their helper and suppressor activities on differentiation of B cells to immunoglobulin-(IgM and IgG) producing cells by a highly sensitive reversed hemolytic plaque assay. The T cell-enriched high density fractions provided help for B cell differentiation to levels higher than that of unfractionated mononuclear cells. On the other hand, the NK-enriched low density fractions did not show helper activity, and when added to the culture of B cells plus helper T cells, they markedly suppressed B cell differentiation. This suppressive activity, as well as the NK cytotoxicity of the NK-enriched fractions, was abrogated by treatment of the cells with monoclonal antibody against human NK cells (HNK-1), but not against T cells (OKT3) in the presence of complement. NK cells also suppressed PWM-driven B cell differentiation in the presence of T4+ (helper/inducer T) but not T8+ (cytotoxic/suppressor T) cells; however, they showed no inhibition of soluble factor-induced B cell differentiation assayed in the absence of helper T cells. It is thus concluded that human peripheral blood NK cells exhibit an ability to suppress PWM-driven B cell differentiation, possibly by acting through the effect on helper T cells but not directly on B cells.     

Oxidized and reduced nicotinamide adenine dinucleotide phosphate levels of plants hardened and unhardened against chilling injury

Pea plants (Pisum sativum L. var. Alaska) subjected to low temperature (5°) in the light acquired resistance against chilling injury.

Unhardened plants maintained high NADP and low NADPH levels during illumination at 25° but hardened plants had low NADP and high NADPH levels in the light. When the unhardened plants were transferred to the dark room at 25°, their NADPH levels decreased immediately. On the other hand, hardened plants maintained a high NADPH level for a few hours even in the dark.

     

Studies on sea-snake venoms. Crystallization of erabutoxins a and b from Laticauda semifasciata venom

1. The toxic principles in the venom of the sea-snake Laticauda semifasciata were separated into two components by CM-cellulose chromatography and obtained in crystalline forms. They were named ;erabutoxins a and b'. 2. The homogeneity of each toxin was shown by rechromatography, by disk electrophoresis, by ultracentrifuging, by toxicity measurements before and after repeated crystallizations and by N-terminal analysis. 3. They had molecular weights of about 7000. Both of them contained 61 (or 62) amino acid residues/molecule. The only difference between erabutoxins a and b was that one of the aspartic acid (or asparagine) residues in erabutoxin a was replaced by a histidine residue in erabutoxin b. 4. Both of the toxins had LD(50) values of 0.15mug./g. body wt. for mice and 0.07mug./g. for rats. It was shown with frog-muscle preparations that they acted on postsynaptic membrane to block neuromuscular transmission.     

Quantitative analysis of serum IL-6 and its correlation with increased levels of serum IL-2R in HIV-induced diseases

We have devised a luminescence sandwich ELISA for the quantification of IL-6 in both sera and cell culture supernatants, which had a detection limit of 100 fg/ml of test sample. By using the luminescence sandwich-ELISA, low but measurable levels of IL-6 (9.5 pg/ml on average) were found in the sera from normal individuals. The serum levels of IL-6 were elevated in HIV-seropositive asymptomatic carriers (55.5 pg/ml on average), and the IL-6 levels were correlated with the degree of HIV-induced disease progression (AIDS-related complex 106.8 pg/ml on average and (AIDS 283 pg/ml). IL-6 immunoreactivity in the sera of AIDS patients eluted at a 25,000 m.w. major peak, which was biologically active and heat-stable, and a 500,000 m.w. minor peak in size-exclusion HPLC. Interestingly, a significant correlation was observed between the serum IL-6 levels and soluble IL-2R levels. In vitro, HIV infection of PHA-activated PBMC led to enhanced release of IL-6 into the culture supernatants. Moreover, soluble IL-2R release was markedly increased by adding exogenous IL-6, whereas it was decreased by adding the neutralizing anti-IL-6 mAb to the cultures. These results demonstrate that increased IL-6 levels are significantly associated with sIL-2R levels, and suggest a cause of the increased levels of this receptor in patients with HIV infection. Furthermore, both serum IL-6 and serum IL-2R levels in HIV infection reflect the stage of the HIV-induced disease.     

Differential regulation of the low affinity Fc receptor for IgE (Fc epsilon R2/CD23) and the IL-2 receptor (Tac/p55) on eosinophilic leukemia cell line (EoL-1 and EoL-3)

Two types of activation Ag, low affinity FcR for IgE (Fc epsilon R2)/CD23 and IL-2R (Tac/p55), were expressed and differently regulated on human eosinophilic leukemia cell lines (EoL-1 and EoL-3). Because the binding of IgE on EoL-3 cells was completely inhibited by H107 (anti-Fc epsilon R2/CD23 mAb) but not by irrelevant mAb, essentially all the low affinity Fc epsilon R2 on EoL-3 seemed to be the Fc epsilon R2/CD23 molecules. Both IL-4 and IFN-gamma enhanced the surface expression of Fc epsilon R2, whereas IL-1, IL-2, and IL-5 showed no effects, as determined by surface staining with anti-Fc epsilon R2 antibody (H107). In contrast to Fc epsilon R2 up-regulation, IL-4 and IFN-gamma showed a differential effect on the regulation of IL-2R (Tac/p55). Whereas IFN-gamma up-regulated the receptor expression of IL-2R/Tac, IL-4 did not. The result suggests that these lymphokines are involved in the different aspects of the activation pathway of the eosinophils. The possible role of Fc epsilon R2 and IL-2R on the function of eosinophils in allergic reaction is discussed.