Incorporation of sulfate by the mouse thymus: its relation to secretion by medullary epithelial cells and to thymic lymphopoiesis

The thymus was examined in suckling mice during normal development and the involution and regeneration produced by injection of cortisol, in experiments designed to test the hypothesis that medullary epithelial cells secrete a ymphopoietic hormone responsible for controlling the magnitude of thymic lymphopoiesis. Cellular events were observed by light and electron microscopy. Lymphopoiesis was assessed, after injection of thymidine-(3)H, by counting the proportion of lymphocytes labeled in radioautographs of thymus. Cortical lymphopoiesis was distributed heterogeneously, being concentrated in the subcapsular region, but medullary lymphopoiesis was statistically homogeneous in distribution and similar in magnitude to the average level of cortical lymphopoiesis in suckling mice. Therefore counts of the labeling index in the medulla were used to estimate the size of the proliferating population of lymphocytes. Epithelial secretory activity was estimated by measuring the incorporation of (36)sulfate by the thymus, using gel filtration chromatography to isolate soluble macromolecular (35)sulfate-presumed on radioautographic evidence to represent the mucoid epithelial secretory product. Incorporated (35)sulfate accumulated rapidly for 4 hr, reached a peak at 12 hr, and had fallen to half that level by 24 hr after a single injection-as would be expected of a secretory product. During normal postnatal development the size of the proliferating population of lymphocytes and the magnitude of (35)sulfate incorporation increased in parallel. During acute involution induced by cortisol both parameters diminished greatly but rose to high levels during subsequent regeneration. Accordingly, lymphopoiesis and sulfate incorporation -as defined and measured in these experiments-correlated linearly over a wide range of variation, providing circumstantial evidence to support the hypothesis that medullary epithelial cells secrete a sulfated mucoid lymphopoietic hormone. This conclusion is discussed in terms of the roles of thymus and adrenal cortex in development of the lymphoid system and maturation of immunological competence.

Authoritarian attitudes and field dependence

This study sought to investigate further the dependency of authoritarian attitudes on field dependence by using a factor analytically derived measure of authoritarian attitudes, the F + D scale. 523 college Ss completed the F + D scale, and the high and low scorers were selected from the extreme ends of the male distribution of 264 Ss. 20 Ss in each extreme group were individually administered Jackson's Short Form of the Embedded Figures Test (EFT), a measure of field dependence. High F + D scorers required significantly more time to complete the EFT than did low F + D scorers. They also obtained significantly lower SCAT verbal and total scores than did low F + D scorers. These two sets of findings were interpreted as resulting from the contrasting cognitive styles of the two F + D groups. It was concluded that, as measured by the tests in this study, high F + D scorers were more field dependent and less intelligent than low F + D scorers.