Primary production and respiration of the phytoplankton in the Blue and White Niles at Khartoum

Phytoplankton production and respiration in the Blue Nile and White Nile at Khartoum were measured during the period November 1969–January 1971 using the light and dark bottle technique. Maximum rates of production coincided with periods of maximum phytoplankton densities. In the Blue Nile gross production varied between 0.00 gCm^–3d^–1 during the flood season and 2.19 gCm^–3d^–1 (0.49 mgO₂l^–1h^–1) during November 1969. In the White Nile the range was from 0.41 gCm^–3d^–1 (0.09 MgO₂l^–1h^–1) in May to 3.74 gCm^–3d^–1 (0.83 MgO₂l^–1h^–1) in November. The maximum rates of respiration in the Blue Nile and White Nile were 0.10 and 0.63 MgO₂l^–1h^–1 respectively. The ratios net:gross production were generally higher in the White Nile than in the Blue Nile.     

Lectin-induced modulation of the antibody response to type III pneumococcal polysaccharide

Several lectins were tested for their capacity to alter the antibody response to type III pneumococcal polysaccharide (SSS-III). The antibody response was enhanced by concanavalin A (Con A), phytohemagglutinin (PHA), as well as lectins from Phytolacca americana (Pa-2), Pisum sativum (PSA), and Lens culinaris (LCH), when these lectins were given 2 days after immunization with SSS-III; however, suppression was obtained when Con A and Pa-2 were given at the time of immunization. By contrast the lectins from Vicia villosa (VVL) and Bauhinia purpurea (BPA) did not alter the antibody response. Since the lectins PSA and LCH bind to the same monosaccharide as Con A, whereas the other lectins bind to different monosaccharides, these findings indicate that there is no relationship between nominal monosaccharide specificity and the capacity to modulate the antibody response. Substantial increases in the magnitude of the IgG₁ antibody response was noted after the administration of Con A whereas profound enhancement of IgG_2a antibody response was noted after PHA was given.     

Studies on the mechanism of the human natural killer cell lethal hit: a new method for rapid physical isolation of lethally hit K562 targets and inhibition of cytolysis by reduced temperature or trypsin

A new method was developed which allows for rapid (2 min) physical isolation of viable K562 target cells after being programmed to lyse (lethally hit) by purified human natural killer (NK) cells (LGL). To achieve this K562 cells which were obtained from the 34-36% interface of discontinuous Percoll gradients and purified human NK cells (LGL) which were obtained from the (43-45% Percoll) interface were employed. Using a Ca2+ pulse method and the separation of NK-K562 conjugates with EDTA and rapid centrifugation on Percoll gradients at 4 degrees C we could physically isolate the lethally hit K562 cells from the LGL allowing the study of the events leading to their subsequent lysis. Lysis of "purified" lethally hit K562 cells occurred in the absence of Ca2+ or Mg2+ and was blocked by reduced temperature (4 degrees C), or by the protease enzyme trypsin. When lethally hit targets were held at 4 degrees C (to block lysis) then rewarmed to 37 degrees C lysis ensued but with a rate slower than that of control cells not held at 4 degrees C. These data support the concept that transfer of protease-sensitive and possibly temperature-dependent structures from the NK cell to the target is a requisite step in NK cytolysis.     

T-cell-mediated regression of "spontaneous" and of Epstein-Barr virus-induced B-cell transformation in vitro: studies with cyclosporin A

The regression of Epstein-Barr (EB) virus-transformed B-cell outgrowth which is seen in experimentally-infected cultures of blood mononuclear (UM) cells from healthy seropositive donors can be abolished in medium containing the T-cell-suppressive agent cyclosporin A (CSA) at concentrations of 0.05 microgram/ml and above. CSA mediates its effect within the first 4 days post-infection of the UM cells and this prevents subsequent in vitro generation of the EB virus-specific cytotoxic-T-cell response which normally brings about regression. Regression can be fully restored by supplementing the CSA-treated culture with interleukin 2 (IL-2)-containing culture supernatants or indeed with purified IL-2 itself, suggesting that CSA mediates its effect in this system through inhibiting the endogenous production of IL-2 which is required to amplify the virus-specific cytotoxic response. "Spontaneous transformation" to EB virus genome-positive lymphoblastoid cell lines in noninfected cultures of UM cells from healthy seropositive donors, though rare in normal medium, is enhanced to such a degree in the presence of CSA that, for many donors, the phenomenon becomes titratable against input cell dose across the 2.0 X 10(6)-2.5 X 10(5) cells/culture range. Cell mixing experiments suggest that the spontaneously transformed cell lines which arise with such efficiency under these conditions do so not by direct in vitro outgrowth of progenitor cells transformed by the virus in vivo, but by a two-step mechanism involving virus release and secondary infection in vitro.     

Unsuccessful induction of low-zone tolerance to bovine serum albumin injected into the subarachnoid space

Introduction of T-dependent antigens into the subarachnoid space (isas) resulted in higher systemic antibody responses in mice than injections into the peritoneal cavity (ip) or other sites commonly used for immunization. Antibody production in isas immunized mice was not increased by treatment with cyclophosphamide (Cy) at doses known to abolish T-suppressor-cell activity, but such treatment increased antibody production in ip immunized mice toward the higher level which was observed in the isas immunized animals. Suppressor cell-dependent low zone tolerance (LZT) to TNP-BSA could not be induced by isas injections of deaggregated BSA (d-BSA). Conversely, mice which were unresponsive to ip injected d-BSA showed consistent systemic antibody responses when the antigen was injected isas. These observations indicate that immune responses initiated within the CNS are associated with relatively ineffective induction of systemic suppressor cell activity.     

Differential effects of positive and negative proliferative stimuli on murine cytolytic and helper T-cell clones

Studies were performed to determine whether substances could be identified which exhibited differential regulatory effects--either positive or negative--on the growth of murine alloreactive cytolytic (Tc) and helper (Th) cloned T-cell lines. The following lines of evidence suggested that Tc and Th proliferate in response to the same growth factor (GF). (1) When GF-containing fluids from cultures of phorbol myristic acetate (PMA)-activated EL4 thymoma were fractionated by a variety of biochemical techniques. Tc and Th eluted together. (2) Absorption of GF-containing supernatants with either cloned Tc or cloned Th depleted GF activity for each to a similar extent, and GF eluted from either Tc or Th to which it had adsorbed supported the proliferation of Tc and Th equally well. (3) Lectin-depleted supernatants from cultures of concanavalin A (Con A)-activated Th stimulated the proliferation of Th as well as Tc. (4) Recombinant human interleukin (IL-2) supported the growth of Tc and Th with equal efficiency. On the other hand, the following observations indicated that Tc and Th differed in their responses to inhibitors of GF-driven proliferation. (1) Con A at greater than or equal to 0.3 micrograms/ml inhibited the GF-driven proliferation of each of three Th lines but not either of two Tc lines. To the contrary, Con A enhanced GF-dependent proliferation of Tc. (2) Like Con A, allogeneic splenocytes selectively depressed GF-driven proliferation of Th but not Tc. (3) A substance generated during the acid elution of GF from cells, possibly a modified fetal calf serum component, greatly reduced the GF-driven proliferation of Tc but not Th. These results suggest that differential control of the proliferation of Tc and Th in cellular immune responses may be achieved via negative regulatory signals and raise the possibility that substances which can selectively depress the proliferation of specific T-cell subsets might be found which would be of therapeutic value.     

Immunological aspects of retinoids in humans. II. Retinoic acid enhances induction of hemolytic plaque-forming cells

The effects of retinoic acid (RA) on the induction of antibody-producing cells from human tonsillar lymphocytes sensitized to sheep erythrocytes (SRBC) have been evaluated. Our results indicated that 10(-5) to 10(-7) M RA caused up to a three-fold increase in the number of plaque-forming cells (PFC) and a qualitative increase in the size of the plaques during the induction of PFC in 5- to 7-day cultures. Enhancement also occurred when tonsil cells were preincubated with RA for 24 hr and then washed, or when RA was added any time in the first 4 days after initiation of the culture. When T- and B-cell fractions were pretreated with RA for 24 hr, washed, and recombined with SRBC, RA-induced augmentation of PFC occurred only in conjunction with RA treatment of the B-cell fraction. Pretreatment of the T-cell fraction had no effect on PFC induction or on the RA-enhanced response when the B-cell fraction was simultaneously treated with RA. Other experiments suggested that RA did not modulate PFC induction by influencing regulatory functions of adherent accessory cells. Our study demonstrates that RA can enhance human antibody responses and shows that this effect is not caused by increased activity of T cells or adherent accessory cells, but is instead the result of a direct effect of RA on B-cell populations.     

Effects of glucagon on the redox states of cytochromes in mitochondria in situ in perfused rat liver

The effects of glucagon on the respiratory function of mitochondria in situ were investigated in isolated perfused rat liver. Glucagon at the concentrations higher than 20 pM and cyclic AMP (75 microM) stimulated hepatic respiration, and shifted the redox state of pyridine nucleotide (NADH/NAD) in mitochondria in situ to a more reduced state as judged by organ fluorometry and beta-hydroxybutyrate/acetoacetate ratio. The organ spectrophotometric study revealed that glucagon and cyclic AMP induced the reduction of redox states of cytochromes a(a3), b and c+c1. Atractyloside (4 micrograms/ml) abolished the effects of glucagon on these parameters and gluconeogenesis from lactate. These observations suggest that glucagon increases the availability of substrates for mitochondrial respiration, and this alteration in mitochondrial function is crucial in enhancing gluconeogenesis.     

Forward mutation assay of V79 cells to 6-thioguanine resistance in a soft agar technique that eliminates effects of metabolic co-operation

A technique involving culture in soft agar was used for the assay of forward mutation of V79 cells to 6-thioguanine (6TG) resistance. The main reason for the use of soft agar was to prevent reduction in recovery of mutants depending on the cell density plated for mutation selection, which is the chief problem in the liquid method, and which results mainly from metabolic co-operation due to cell-to-cell contact.V79 cells grew well in fortified soft agar medium (DMEM + 20% FBS) showing cloning efficiencies (>80%) as high as in liquid culture. Therefore, V79/HGPRT mutagenesis could be assayed quantitatively in soft agar culture.The frequency of 6TG-resistant colonies in agar selective medium increased linearly with increase in concentration of EMS. Toxicity and mutagenic responses were greater in soft agar than in liquid culture.In cultures of untreated and EMS-treated cells, more than 95% of the 6TG-resistant colonies isolated were aminopterin-sensitive.Use of soft agar for selection prevented the reduction in the number of mutants with increase in the size of incula on plating up to 1?2 × 10⁶ cells per 9-cm dish: in liquid culture, even with a lower plating number (2 × 10⁵ cells per 9-cm dish), a notable reduction in numbers of mutants was observed. This character was re-examined in a reconstruction experiment. The results show that, when up to 2 × 10⁶ cells were plated per 9-cm dish, 6TG-resistant cells were almost completely recovered from the soft agar medium, whereas only 10% were recovered from liquid culture.     

125I] 3-quinuclidinyl 4-iodobenzilate: a high affinity, high specific activity radioligand for the M1 and M2-acetylcholine receptors

We have prepared a radioiodinated ligand which binds with high affinity to the muscarinic acetylcholine receptor (m-AChR). A derivative of 3-quinuclidinyl benzilate, [125I] labeled (R) 1-aza-bicyclo(2.2.2)oct-3-yl (R,S)-alpha-hydroxy-alpha-(4-[125I]iodophenyl)phenyl acetate (4- IQNB ) exhibits an affinity for the m-AChR from corpus striatum higher than that of (R) [3H] QNB. Additionally, [125I] 4- IQNB exhibits receptor selectivity for the M1 receptor since the affinity for the receptor from dog and rat heart is lower than that using dog or rat corpus striatum.