Accumulation of eosinophils and monocytes in lymphoid organs of chick-embryos. II. Effect of mitogenic stimulation.

The mitogen effect on migration of eosinophils and monocytes was studied in embryonic chickens. On the 13th embryonic day, chickens were injected with mitogens, such as concanavalin A (Con A), phytohemagglutinin-P (PHA-P), and lipopolysaccharide (LPS), into the allantoic cavity, and the mitogenic effect was estimated from the relative frequencies of eosinophils and monocytes by enumerating the number of oxidase positive cells (OPC) in the spleen, thymus, and bursa of Fabricius. Splenic frequencies of OPC increased in the embryos treated with mitogens. Similar influences were also detected in the thymic OPC. Higher responses were seen on the 18th embryonic day in the number of splenic OPC when embryos were treated with Con A or PHA-P than with LPS. These findings suggest that Con A and PHA-P are preferential OPC accumulation promoters. However, bursal frequencies of OPC in the cortex were low after mitogenic stimulations when compared with controls, although appreciable responses were detected in the bursal medulla after LPS stimulation. These results suggest that the migration pattern in the population of eosinophils and monocytes is affected not only by T cell mitogens but is also derived from LPS stimulation.