The distribution of the major histocompatibility complex (MHC) antigens in the unfixed human testicle was studied by indirect immunofluorescence. Three murine monoclonal antibodies to the common determinants of class I MHC antigens (human leukocyte antigen [HLA]-ABC) and three against class II MHC antigens (HLA-D/DR antigens), respectively, were utilized. No class I MHC antigens were identified on developing testicular germ cells including spermatozoa, but interstitial cells between the seminiferous tubules (including Leydig cells) and blood vessel endothelium expressed the antigen. Class II MHC antigens were not found on any cells within the seminiferous tubules. However, the class II antigen was identified on dendritic-like cells between the seminiferous tubules and on vessel endothelium, although its expression was expectedly limited. These findings indicate that human testicular germ cells express minimal or no MHC antigens.

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The temporal schedule of DNA replication in heat-synchronized Tetrahymena was studied by autoradiographic and cytofluorometric methods . It was shown that some cells, which were synchronized by selection of individual dividing cells or by temporary thymidine starvation, incorporated [3 H]thymidine into macronuclei in a periodic fashion during the heat-shock treatment . It was concluded that supernumerary S periods occurred while cell division was blocked by high temperature . The proportion of cells which initiated supernumerary S periods was found to be dependent on the duration of the heat-shock treatment and on the cell cycle stage when the first heat shock was applied . Cytofluorometric measurements of Feulgen-stained macronuclei during the heat-shock treatment indicated that the DNA complement of these cells was substantially increased and probably duplicated during the course of each S period . Estimates of DNA content also suggested that the rate of DNA synthesis progressively declined during long heat-shock treatments . These results indicate that the mechanism which brings about heat-induced division synchrony is not an interruption of the process of DNA replication. Further experiments were concerned with the regulation of DNA synthesis during the first synchronized division cycle . It was shown that participation in DNA synthesis at this time increased as more cells were able to conclude the terminal S period during the preceding heat-shock treatment . It is suggested that a discrete period of time is necessary after the completion of DNA synthesis before another round of DNA synthesis can be initiated .

Anatomic study of placental dysfunction may benefit from the applications of new routine techniques. Immunohistochemical staining for human placental lactogen (HPL) was used in 3 cases illustrating different perinatal disorders. The amount of HPL labeling ranged from high in an acute anoxic death due to abruptio placentae, through decreased in a case of maternal hypertension, to low in severe intrauterine growth retardation. Such information complements standard clinical and pathologic studies. Ten percent buffered Formalin was superior to Bouin's fixative and alcoholic Formalin for the demonstration of HPL. Even after 4 days of refrigeration at 4 degrees C, all of the syncytiotrophoblastic tissue was labeled in sections of paraffin-embedded, Formalin-fixed normal placentas.