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In order to evaluate the importance of gestational age and the dose-incidence relationship by gamma radiation, pregnant ICR mice at gestational days from 2.5 to 15.5 days post-coitus (p.c.) were exposed to a single dose of 2.0 Gy and also at day 11.5 after conception, which was the most sensitive stage for the induction of major congenital malformations. The animals were sacrificed on day 18 of gestation and the fetuses were examined for mortality, growth retardation, changes in head size and other morphological abnormalities. The only demonstrable effect of irradiation during the pre-implantation period was an increase in prenatal mortality. Resorptions were maximal on exposure at day 2.5 after conception. The pre-implantation irradiated embryos which survived did not show any major fetal abnormalities. A small head, growth retardation, a cleft palate, dilatation of the cerebral ventricle, a renal pelvis, and abnormalities of the extremities and tail after exposure were prominent during the organogenesis period, especially on day 11.5 of gestation. As for the dose-incidence relationship, the incidence of a small head, growth-retarded fetuses, a cleft palate, dilatation of cerebral ventricle and abnormalities of the extremities in live fetuses rose as the radiation dose increased. The result indicated that the late period of organogenesis in the development of the brain, skull and extremities of a mouse was a particularly sensitive phase. The threshold doses of radiation that induced a cleft palate and dilatation of the cerebral ventricle, and abnormal extremities were between 1.0 and 2.0 Gy, and between 0.5 and 1.0 Gy, respectively.

We report on application offlow cytometnic and immunogold labeling techniques to purify and identify two types of munine epidermal dendnitic cells: Langerhans cells (LC) and Thy-1-positive dendnitic epidermal cells (Thy 14-dEC). After density centnifugation ofepidermal cell (EC) suspensions through Ficoll gradients, IA-positive LC and Thy P-dEC are labeled with monoclonal antibodies (fluorescein-conjugated anti-IA for LC and anti-Thy 1.2-biotin, followed by avidin-phycoerythnin, for Thy P-dEC). The fluorescence-activated cell sorter (FACS) is then used to obtain 95-98% pure populations of these dendnitic cells with a yield of 2-4 x 106 cells and a viability of8O-90%. A post-fixation, pre-embedding immunogold labeling technique using 15 nm and 40 nm

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