SKINS*

If viable suspensions of normal homologous lymphoid ceils are inoculated into the skins of tmsensitized guinea pigs (1), hamsters (2), rabbits (3, 4), men (5), or chickens (6, 7), they may provoke slowly developing cutaneous inflammatory reactions. If homologous ceils, lymphoid or otherwise, are injected into the skins of specifically presensitized hosts of these species, somewhat similar reactions, usually referred to as "direct reactions", are elicited (2--4, 8); but their onset is more rapid. Both of these cutaneous reactivities are believed to be manifestations of hypersensitivity to cellular transplantation antigens. The first type of reaction results from an in situ sensitization on the part of the inoculated immunologicaUy competent cells against the alien antigens of their host. The second type of reaction expresses the host's sensitivity to the inoculated foreign ceils. This paper describes quantitative studies designed to define the various cutaneous reactivities incitable in hamsters ' skins by inoculation of various types of cellular inocula under different immunogenetic conditions, and to elucidate their etiology. Materials and Methods The hamsters (Mesocrivetus auratus) used belonged to three different isogenic strains, MHA, CB, and LSH, and their Fx hybrids. MHA's are albino, while CB and LSH animals ar

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Potential Inhibitory Role of the Hypoxia-Inducible Transcription Factor Mash-2 (Mammalian Achaete-Scute

The human placenta has a remarkable capacity to aromatize C 19-steroids, produced by the fetal adrenals, to estrogens. This reaction is catalyzed by aromatase P450 (P450arom), encoded by the CYP19 gene. In placenta, CYP19 gene expression is restricted to the syncytiotrophoblast layer. Cytotrophoblasts isolated from human placenta, when placed in monolayer culture in 20 % O 2, spontaneously fuse to form syncytiotrophoblast. These morphological changes are associated with a marked induction of aromatase activity and CYP19 gene expression. When cytotrophoblasts are cultured in an atmosphere containing 2 % O 2, they manifest increased rates of DNA synthesis and fail to fuse and form syncytiotrophoblast. The objective of the present study was to utilize cytotrophoblasts isolated from midterm human placenta to analyze the effects of O 2 on CYP19 gene expression and the molecular mechanisms that mediate these effects. We observed that when trophoblast cells were maintained in 2 % O 2, there was only a modest induction of CYP19 expression as a function of time in culture, and aromatase activity was barely detectable. However, when cytotrophoblasts that had been maintained in 2 % O 2 for 3 days were placed in a 20 % O 2 environment, there was a rapid onset of cell fusion and induction of P450arom mRNA and aromatase activity. In addition, mRNAs for the helix-loop-helix factors Mash-2 (mammalian achaete-scute homologous protein-2) and Id