Aging and Cancerigenesis. II. Effect of Age on Phagocytic Activity of the Reticuloendothelial System and on Tumor Growth2

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Abstract
A possible correlation between aging, phagocytic capacity of the reticuloendothelial system and growth of Ehrlich ascites tumor was studied in female Swiss ICR/Ha mice. In untreated mice, the phagocytic index K for clearance of colloidal carbon was greater in young adults (3 months old) than in older (8 or 18 months old) animals. Zymosan treatment caused the most significant increase in phagocytic activity in 3-month-old mice and least in 18-month-old mice. Intraperitoneal transplants of Ehrlich ascites tumor resulted in the most rapid proliferation in 18-month-old mice; the 3-month-oid animals maintained the largest K during tumor growth. Ehrlich ascites grew in all 8- and 18-month-old mice treated with zymosan, but was rejected in 6 of 41 young adults similarly treated. In this experiment, K for 3-month-old mice peaked a second time before decreasing gradually to its base level, in contrast to the maintenance of a moderately high phagocytic index in mice treated similarly with zymosan but not inoculated with tumor. Carbon clearance for the 8- and 18-month-old mice resembled that seen previously with zymosan alone.
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