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1221. Possible demographic consequences of AIDS in developing countries.
Simple mathematical models of the transmission dynamics of HIV that incorporate demographic and epidemiological processes to assess the potential impact of AIDS on human population growth and structure in developing countries suggest that AIDS is capable of changing population growth rates from positive to negative values over timescales of a few decades. The disease is predicted to have little if any impact on the dependency ratio of a population, defined as the number of children below age 15 years and elderly people over 64 years, divided by the number of adults between 15 to 64 years.
1222. Peptide growth factors are multifunctional.
The actions of many peptide growth factors include both stimulation and inhibition of cell proliferation, as well as effects unrelated to the control of cell growth. One peptide can have both stimulatory and inhibitory activity in a single cell, depending on the context of the other signal molecules present.
1223. T-cell receptor V beta use predicts reactivity and tolerance to Mlsa-encoded antigens.
作者: H R MacDonald.;R Schneider.;R K Lees.;R C Howe.;H Acha-Orbea.;H Festenstein.;R M Zinkernagel.;H Hengartner.
来源: Nature. 1988年332卷6159期40-5页
T lymphocytes reactive with the product of the Mlsa-allele of the minor lymphocyte stimulating (Mls) locus use a predominant T-cell receptor beta-chain variable gene segment (V beta 6). Such V beta 6-bearing T cells are selectively eliminated in the thymus of Mlsa-bearing mice, consistent with a model in which tolerance to self antigens is achieved by clonal deletion.
1224. Self-tolerance eliminates T cells specific for Mls-modified products of the major histocompatibility complex.
In mice the product of the Mlsa locus is an unusual antigen capable of interaction with certain products of the major histocompatibility locus (MHC) to form a ligand for a large portion of the T-cell alpha/beta receptor repertoire, including nearly all receptors that use V beta 8.1. The presence of Mlsa/MHC during T-cell development results in the deletion of T cells that express V beta 8.1, documenting the importance of clonal deletion in establishing tolerance to self antigens.
1233. A human retinoic acid receptor which belongs to the family of nuclear receptors.
A cDNA encoding a protein that binds retinoic acid with high affinity has been cloned. The protein is homologous to the receptors for steroid hormones, thyroid hormones and vitamin D3, and appears to be a retinoic acid-inducible trans-acting enhancer factor, suggesting that the molecular mechanisms of the effect of retinoids (vitamin A) on embryonic development, differentiation and tumour cell growth are similar to those described for other members of this nuclear receptor family.
1239. Functional inactivation of genes by dominant negative mutations.
Molecular biologists are increasingly faced with the problem of assigning a function to genes that have been cloned. A new approach to this problem involves the manipulation of the cloned gene to create what are known as 'dominant negative' mutations. These encode mutant polypeptides that when overexpressed disrupt the activity of the wild-type gene. There are many precedents for this kind of behaviour in the literature--some oncogenes might be examples of naturally occurring dominant negative mutations.
1240. A new T-cell receptor gene located within the alpha locus and expressed early in T-cell differentiation.
A new T-cell receptor gene lies just 5' to the J alpha C alpha coding regions. Its placement in this location suggests a novel mechanism for the regulation of expression of one T-cell receptor polypeptide to another during ontogeny. Rearrangement of this locus occurs very early in thymic differentiation and its RNA expression parallels that of the gamma-chain in thymic subpopulations, making this a possible candidate for the recently described delta-chain of the T-cell receptor.
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