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991.
Michael F. Cole Sean P. Fitzsimmons Michael J. Sheridan Yong Xu 《Microbiology and immunology》1995,39(8):591-598
The levels, specificity and avidities of serum IgM and IgG antibodies reactive with Actinobacillus actinomycetemcomitans (Aa) serotypes a, b and c were determined in periodontally healthy (PH) children and compared with subjects with localized juvenile periodontitis (LJP). All PH children exhibited IgM and IgG Aa-reactive antibodies whether or not Aa was detected subgingivally but the antibodies were not specific for Aa. In contrast, LJP sera contained high concentrations of IgM and IgG antibodies reactive with Aa that were largely specific for this bacterium. IgM and IgG antibodies in both PH and LJP subjects were of low avidity. With one exception, the avidities of IgG anti-Aa antibodies were significantly greater than those of IgM antibodies in both PH and LJP subjects. However, although the LJP subjects had as much as 115-fold more Aa-reactive IgG antibody than did the PH subjects the avidities of their IgG antibodies were no greater than those of the PH group. The induction by the host of low-avidity antibodies, that are ineffective in immune elimination, may be a reason why commensal bacteria persist at mucosal surfaces and why persons with LJP fail to eliminate Aa from their periodontal pockets. 相似文献
992.
Chi-Keong Ong Sean Nee Andrew Rambaut Hans-Ulrich Bernard Paul H. Harvey 《Journal of molecular evolution》1997,44(2):199-206
Using gene genealogies constructed from gene sequence data, we show that both the mucosal and cutaneous papillomaviruses
(PV)—supergroups A and B—appear to have been transmitted through susceptible populations faster than exponentially. The data
and methods involved (1) examining the PV database for phylogenetic signal in an L1 open reading frame (ORF) fragment and
an E1 ORF segment, (2) demonstrating that the same two fragments have evolved in a way consistent with a molecular clock,
and (3) applying methods of phylogenetic tree analysis that test different scenarios for the dynamics of viral transmission
within populations. The results indicate increases in PV populations of both supergroups A and B in the recent past. This
form of the increases, which fit a null model of population growth with an exponent increasing in time, is compatible with
the fact that human populations have grown at a faster than exponential rate, thus increasing the numbers of susceptible hosts
for HPVs. There are, however, indications that the population of supergroup A has now stopped increasing in size.
Received: 4 June 1996 / Accepted: 12 August 1996 相似文献
993.
Northern elephant seal pups ( Mirounga angustirostris ) use several physiological mechanisms to conserve water during their 8- 12-wk postweaning fast. Urine was analyzed from five animals and plasma from four of those animals was sampled serially throughout the postweaning period to quantify changes in urine concentrating ability and electrolyte homeostasis at various stages of the fast (Early = 1-4 wk, Mid = 4-7 wk, Late = 7-10 wk). Plasma osmolarities stayed relatively constant at 301.6 f 13.1 mOsm/kg. Urine osmolarities ranged from 1,053.5 ± 78.6 mOsm/kg (Early), to 1,585.0 ± 136.7 mOsm/kg after eight weeks, dropping to 1,214.3 ± 349.6 mOsm/kg (Late). Urine concentrations for Na+ and K+ early in the fast were 55.0 ± 14.6 mM and 180.8 ± 48.6 mM, respectively, declining to 8.2 ± 3.3 mM and 91.4 ± 29.0 mM later. Plasma vasopressin concentrations ranged from 34.8 ± 18.2 pg/ml (Early) to 4.8 ± 1.3 pg/ml (Late). The pups appear to conserve their body water by producing a concentrated urine, thus reducing urinary water loss. The significance of the antidiuretic role of vasopressin in the conservation of body water in these pups could not be conclusively determined from the results. 相似文献
994.
Sean C. Thomas 《Global Change Biology》2005,11(2):197-202
Globally increasing atmospheric CO2 concentrations are known to affect many aspects of plant physiology and development; however, little attention has been given to leaf and canopy optical properties. Three tropical trees in the Leguminosae, an important canopy tree family in many tropical forests, responded similarly to an experimental doubling of CO2 partial pressure with a 9–23% increase in spectral leaf reflectance to light in the visible (400–700 nm) waveband. Decreased leaf chlorophyll content under elevated CO2 may explain part of the observed increase in reflectance. However, analyses that statistically corrected for chlorophyll content effects on reflectance still indicated a significant CO2 effect. This results, in conjunction with the spectral pattern of the response, suggests that the primary mechanism is increased optical masking of chlorophyll under elevated CO2. The magnitude of the increase in leaf reflectance is sufficient to suggest that increased canopy reflectance of tropical forests (and possibly other terrestrial ecosystems) may be an important negative feedback in the response of global net radiative climate forcing to increasing atmospheric CO2. 相似文献
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997.
Yvonne Aratyn-Schaus Francesco S. Pasqualini Hongyan Yuan Megan L. McCain George J.C. Ye Sean P. Sheehy Patrick H. Campbell Kevin Kit Parker 《The Journal of cell biology》2016,212(4):389-397
The efficacy of cardiac cell therapy depends on the integration of existing and newly formed cardiomyocytes. Here, we developed a minimal in vitro model of this interface by engineering two cell microtissues (μtissues) containing mouse cardiomyocytes, representing spared myocardium after injury, and cardiomyocytes generated from embryonic and induced pluripotent stem cells, to model newly formed cells. We demonstrated that weaker stem cell–derived myocytes coupled with stronger myocytes to support synchronous contraction, but this arrangement required focal adhesion-like structures near the cell–cell junction that degrade force transmission between cells. Moreover, we developed a computational model of μtissue mechanics to demonstrate that a reduction in isometric tension is sufficient to impair force transmission across the cell–cell boundary. Together, our in vitro and in silico results suggest that mechanotransductive mechanisms may contribute to the modest functional benefits observed in cell-therapy studies by regulating the amount of contractile force effectively transmitted at the junction between newly formed and spared myocytes. 相似文献
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999.
Christina M. Sloan-Heggen Amanda O. Bierer A. Eliot Shearer Diana L. Kolbe Carla J. Nishimura Kathy L. Frees Sean S. Ephraim Seiji B. Shibata Kevin T. Booth Colleen A. Campbell Paul T. Ranum Amy E. Weaver E. Ann Black-Ziegelbein Donghong Wang Hela Azaiez Richard J. H. Smith 《Human genetics》2016,135(4):441-450
1000.