The Autofluorescent Cells of the Rat Thymus Under Certain Experimental Conditions.

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Abstract
Summary Autofluorescent cells, having abundant lipoid granules, were previously found at the cortico-medullary junction in the thymi of 10-week-old rats. In this investigation, rats were treated variously to test possibilities concerning the undetermined nature of these cells. First, rats aged 5 weeks were adrenalectomized or orchiecto-mized and killed when aged 3 months. In their non-involuted thymi, the pattern of autofluorescent cells was as in the differentially involuted thymi of normal rats of the same age. This indicated that the development of these cells is not dependent on a process starting with thymic involution. Secondly, rats aged 3 weeks were placed on a fat-free diet until they reached 10 weeks. Their considerably involuted thymi contained as many autofluorescent cells as thymi of normal rats of the same age. This revealed the endogenous origin of the lipids of their granules as well as the fact that the formation of these cells is independent of thymic lympho-cytopoiesis and lympholysis, both phenomena having been considerably reduced by the inanition. Finally, rats aged 2 months were cortisone-treated or the thymus was irradiated. Thymic autofluorescent cells remained at the cortico-medullary junction while, in the cortex, macrophages were actively engulfing degenerating lymphocytes. This demonstrated that the thymic autofluorescent cells are not mobilizable macrophages. The author thanks Mrs. M. Koekebakker for her devoted technical help.