Factors influencing the rate of electron transport in different respiratory pathways of bacteria

The rate of electron transfer by a respiratory pathway as dependent on pH, temperature, concentration of cyanide and concentration of azide was followed in washed non-growing cells ofCitrobacter. Three respiratory pathways leading to three terminal electron acceptors, i.e. oxygen, tetrathionate and nitrate, were investigated. It was found that these pathways mutually differ in their response to pH, temperature, cyanide and azide and conditions favouring inhibition or stimulation of one electron transport pathway relatively to the other two pathways were established.     

Analysis of hybrid H-2D and L antigens with reciprocally mismatched aminoterminal domains: functional T cell recognition requires preservation of fine structural determinants

Studies of immune recognition of hybrid class I antigens expressed on transfected cells have revealed an apparent general requirement that the N(alpha 1) and C1(alpha 2) domains be derived from the same gene in order to preserve recognition by virus-specific H-2-restricted and allospecific T cells. One exception has been the hybrid DL antigen in which the N domain of H-2Ld has been replaced by that of H-2Dd. Cells bearing this molecule serve as targets for some virus and allospecific CTL. Because cells expressing the reciprocal hybrid LD (N domain of H-2Dd replaced by that of H-2Ld) antigen have not been available, it has not been possible to evaluate whether this exception stemmed from the relatedness of H-2Ld and H-2Dd or whether the DL antigen fortuitously preserved some function of the parent molecule as a rare exception. To assess this question, and to evaluate the contribution of the N and C1 domains of H-2Ld and H-2Dd to serologic and T cell recognition, we have constructed the reciprocal chimeric gene pLD (the N exon of H-2Ld substituted for that of H-2Dd), introduced this into mouse L cells by DNA-mediated gene transfer, and analyzed the expressed product biochemically, serologically, and functionally. Transformant L cells expressing either LD or DL antigens were both reactive with a number of anti-H-2Ld or anti-H-2Dd N/C1-specific monoclonal antibodies, indicating the preservation in the hybrid molecules of determinants controlled by discrete domains. Mab binding was generally greater with cells expressing hybrid DL antigen than with those transformants expressing LD molecules. Moreover, the amount of beta 2M associated with DL antigens was more than that associated with LD. Cells expressing hybrid DL antigens were recognized as targets by bulk and cloned allospecific anti-H-2Dd and anti-H-2Ld CTL, whereas cells expressing LD molecules were not recognized by any of the T cells tested. VSV-specific H-2Ld-restricted CTL failed to lyse VSV-infected targets expressing either DL or LD. These results indicate that T cell reactivity of cells expressing the DL hybrid antigen is an exception to the observed general requirement for class I antigens to possess matched N and C1 domains for functional T cell recognition by T cells restricted to parental antigens.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of CNS-active drugs on TRH-induced prolactin release

The effects of several central acting drugs upon thyrotropin-releasing hormone (TRH)-induced increases in prolactin (PRL) release were compared in estrogen-primed male rats. Administration of the serotonin antagonist, p-chlorophenylalanine, or the opiate antagonist, naltrexone, did not alter TRH-induced release of PRL. Pre-treatment with either the dopamine agonist, piribedil, or the cholinergic agonist, pilocarpine, resulted in significantly reduced TRH-induced PRL release. Pilocarpine did not inhibit the TRH-induced increase in PRL release when rats were first pre-treated with the dopamine receptor blocker, haloperidol. These results indicate that the dopaminergic and cholinergic systems can modify TRH-induced release of PRL in vivo.     

Genetic variation within and among lion tamarins

The golden lion tamarin Leontopithecus rosalia rosalia, one of the rarest and most endangered of New World primates, has been the focus of an intensive research and conservation effort for two decades. During that period, managed breeding from 44 founders has brought the captive population to over 400 individuals, a number that equals or exceeds the estimated number of free-ranging golden lion tamarins. The extent of genetic variation among golden lion tamarins was estimated with an electrophoretic survey of 47 allozyme loci from 67 captive and 73 free-ranging individuals. The amount of variation was low, compared to 15 other primate species, with 4% of the loci being polymorphic (P), and with an average heterozygosity H estimate of 0.01 in these callitrichids. Electrophoretic analyses of captive and free-ranging animals (N = 31) of two allopatric morphotypes, Leontopithecus rosalia chrysopygus and L. r. chrysomelas, were similar to the L. r. rosalia findings insofar as they also revealed limited genetic polymorphism. Computation of the Nei-genetic distance measurements showed that the three morphotypes were genetically very similar, although discernible differentiation had occurred at two loci. These data are consistent with the occurrence of recent reproductive isolations of these subspecies.     

Reduced ability of naloxone to stimulate LH and testosterone release in aging male rats; possible relation to increase in hypothalamic met5-enkephalin

Blood luteinizing hormone (LH) and testosterone levels are lower in old than in young male rats. The specific opiate antagonist, naloxone, previously shown to increase serum LH in mature male rats, exhibited relatively little ability to raise serum LH and testosterone levels in old (18–20 mo) as compared to young (4–5 mo) male rats. The brain opiate, met⁵-enkephalin, which depresses LH, was found to be significantly higher in the hypothalamus of old than of young male rats. These observations suggest that hypothalamic opiates may be partially responsible for the lower serum LH and testosterone levels in old male rats, and for reduced release of these hormones in response to naloxone administration.     

A host of hypercholesterolaemic homozygotes in South Africa.

From 1972 to 1979 34 patients with homozygous familial hypercholesterolaemia were seen in one clinic in Johannesburg. All were Afrikaners and most lived in Transvaal Province. Their epidemiological, genetic, clinical, and biochemical characteristics were studied. The course of the disease varied considerably among the 34 patients, with no fewer than six surviving into their fourth or fifth decades. In some patients arterial atheroma was severe while cutaneotendinous xanthomas were slight and vice versa. Coronary heart disease was common but peripheral and cerebral arterial disease was rare. Another prominent finding was high concentrations of low-density lipoprotein cholesterol coupled with low high-density lipoprotein cholesterol values. The prevalences of homozygotes and heterozygotes with familial hypercholesterolaemia in Transvaal Afrikaners, calculated from this group of patients, were 1 in 30,000 and 1 in 100 respectively. These figures are the highest ever reported and may help to explain why South African whites have the highest death rate from coronary heart disease in the Western world.     

Antigen-presenting cells that induce anti-H-2K T-cell responses: Differences in stimulator-cell requirements for induction of proliferation and cell-mediated lympholysis

Splenic T or B cells, which have been depleted of adherent cells by passage through Sephadex G10 columns, fail to stimulate allogeneic lymph-node cells (LN) in primary mixed lymphocyte reactions (MLR) both when the stimulating antigens are H-2 plus Ia and H-2K only. This failure cannot be ascribed to lack of viability of G10-passed cells, since by dye exclusion they are 95 percent viable and can be induced to proliferate in vitro by exposure to LPS or allogeneic cells. Stimulation of MLR activity could be restored by addition of small numbers of plastic-adherent spleen cells (SAC) which had to be syngeneic with the G10-passed stimulator cells. Further, SAC alone without G10-passed cells induced MLR activity which was, on a cell-for-cell basis, 40 times more effective than that induced by unfractionated spleen cells. If the SAC were first depleted of Ia⁺ cells, no stimulation was obtained. This result was observed both in cases where responder and stimulator strains differed across the entireH-2-gene complex and in a mutant-wild type combination (CBA and H-2^km1) in which the difference between the two strains has been mapped to theK region only. These results indicate that Ia⁺ SAC contain a subset(s) of cells which are responsible for stimulation in MLR, regardless of whether the alloantigenic differences involve either Ia or H-2K. In contrast to the inability of G10-passed splenic cells to stimulate MLR activity, these cells were able to stimulate CTL from cytotoxic T lymphocyte precursors (CTL.P) in combinations where the antigenic differences between responder and stimulator were at the entireH-2 complex or atH-2K only. However, SAC were more potent stimulators of cell-mediated lympholysis (CML) activity on a cell-for-cell basis. Thus, either CTL.P can be stimulated by nonadherent spleen cells or they are specifically sensitive to a small subpopulation of contaminating cells that cannot readily be removed by G10 passage.     

The Q7 alpha 3 domain alters T cell recognition of class I antigens.

In this study we have analyzed the role of the alpha 3 domain of class I molecules in T cell recognition. Using the laboratory engineered molecules LLQQ (alpha 1/alpha 2 from Ld, alpha 3, and phosphatidyl inositol (PI) linked C terminus from Q7) and LLQL (alpha 1/alpha 2 from Ld, alpha 3 from Q7, transmembrane (TM) and cytoplasmic domains from Ld) we show that these molecules are not recognized by primary Ld-specific CTL. The cell membrane expression of both Ld and LLQL are upregulated by co-culture with an exogenously supplied murine cytomegalovirus-derived peptide indicating that the Q7 alpha 3 domain does not interfere with binding of Ag to alpha 1/alpha 2. However, only peptide pulsed Ld but not LLQL target cells are recognized by Ld-restricted-peptide specific CTL. In contrast to the above results, LLQL and LLQQ molecules can be recognized by bulk alloreactive anti-Ld CTL and 2/3 of CTL clones derived from in vivo primed mice. The fact that these secondary CTL recognize LLQQ indicates that a PI linkage is permissive for presentation of class I epitopes to alloreactive CTL. These secondary CTL are resistant to blocking at the effector stage by mAb against CD8 and express relatively low levels of membrane CD8 molecules compared to CTL from unprimed mice. Further, culture of unprimed CTL precursors in the presence of CD8 mAb also allows for the generation of CD8-independent CTL that recognize LLQL. Taken together, these data indicate that the alpha 3 domain of Q7 (Qa-2) prevents CD8-dependent CTL from recognizing Ld, regardless of whether the class I molecule is attached to the cell surface by a PI moiety or as a membrane spanning protein domain. We hypothesize that this defect in recognition is most likely due to an inability of CD8 to interact efficiently with the Q7 alpha 3 domain and could account for why Q7 molecules do not serve as restricting elements for virus and minor H-Ag-specific CTL.     

Two roles for CD4 cells in the control of the generation of cytotoxic T lymphocytes.

The generation of CTL against Qa-1 Ag in C57BL/6 (B6) (Qa-1b) and B6.Tlaa (Qa-1a) congenic strains requires in vivo priming with the Qa-1 alloantigen together with a helper Ag, such as H-Y. The primed precursors obtained from these female mice generate Qa-1-specific CTL activity upon culture in vitro. Although the presence of the H-Y helper Ag is not required for the in vitro sensitization, no response occurs in the absence of CD4 cells. Addition of unprimed B6.Tlaa CD4 cells from Qa-1 incompatible radiation bone marrow chimeras (B6.Tlaa----B6), that are presumably tolerant to Qa-1b, provide helper activity for Qa-1b-specific CTL. This indicates that although CD4 cells are obligatory for the Qa-1 response, they need not be specific for alloantigens on the APC to generate helper activity in in vitro cultures. Addition of unirradiated B6 CD8-depleted spleen cells to CD4-depleted B6.Tlaa anti-B6 cultures in the presence of either B6.Tlaa CD4 cells or rIL-2 prevents the generation of Qa-1 specific CTL. This inhibition is not due to an anti-idiotypic Ts cell since B6.Tlaa----B6 chimeric cells do not suppress an anti-Qa-1b response. Rather, this finding is consistent with that of a veto cell mechanism. To determine whether CD4 cells themselves exhibit veto activity, highly purified CD4 populations were tested for their ability to inhibit the generation of Qa-1-specific CTL. CD4 cells precultured for 2 to 3 days with Con A and rIL-2 specifically inhibit CTL activity whereas resting cells do not, similar to that noted for CD8 veto cells. The relative efficiency of activated CD4 cells is greater than that of resting NK cells but is less than that of activated CD8 or NK cells. Thus, CD4 cells not only provide helper activity for CTL precursors, but also act as veto cells to prevent the generation of CTL activity.     

Specificity of a retinoic acid response element in the phosphoenolpyruvate carboxykinase gene promoter: consequences of both retinoic acid and thyroid hormone receptor binding.

The ability of a retinoic acid (RA) response element (RARE) in the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter to mediate effects of either RA or thyroid hormone (T3) on gene expression was studied. Fusion gene constructs consisting of PEPCK promoter sequences ligated to the chloramphenicol acetyltransferase (CAT) reporter gene were used for this analysis. While T3 induced CAT expression to a small degree (about twofold) when such constructs were transiently transfected into H4IIE rat hepatoma cells, along with an expression vector encoding the alpha subtype of the T3 receptor (TR), this effect was mediated by promoter sequences distinct from the PEPCK RARE. Although TRs were capable of binding the PEPCK RARE in the form of putative monomers, dimers, and heterodimers with RA receptors (RARs), this element failed to mediate any positive effect of T3 on gene expression. In contrast, the PEPCK RARE mediated six- to eightfold induction of CAT expression by RA. When TRs were coexpressed along with RARs in transfected H4IIE cells, this RA induction was substantially blunted in a T3-independent manner. This inhibitory effect may be due to the binding of nonfunctional TRs or TR-RAR heterodimers to the PEPCK RARE. A model is proposed to explain the previously observed in vivo effects of T3 on PEPCK gene expression.