Effects of thymectomy on blood neutrophils phagocytic activity and phagocytic response in mice

The role of the thymus in maintenance of the basal phagocytosis of blood neutrophils and eliciting the phagocytic response, induced by i.v. Escherichia coli, was studied in 9 NMRI thymectomized and in 12 control mice. Thymectomy depresses the percentage of phagocyting neutrophils from 70.91 +/- 0.9 (mean +/- SEM) in controls, to 61.49 +/- 2.33 in the thymectomized rats. Phagocytic activity, as assessed by the number of bacteria engulfed by 100 neutrophils, was also lower in thymectomized mice (114.42 +/- 7.52) than in controls (163.71 +/- 4.53). A phagocytic response to i.v. Escherichia coli could nevertheless be noted in thymectomized mice, their phagocytic activity rising from the basal activity of 114.42 +/- 7.52 to 142.19 +/- 5.40 three hours after injection of Escherichia coli, while in control animals this activity rose from 163.71 +/- 4.53 to 216.46 +/- 12.91. These results may, at least partially, explain the recurrent infections and the septicemia occurring in children with Down's syndrome. It is suggested that the thymus, as an endocrine organ, may be involved in maintaining the basal phagocytic activity of blood neutrophils, while the phagocytic response is modulated by extrathymic mechanisms.