Distribution of eosinophils along and across successive segments of the rat digestive tract: a quantitative study

Density of eosinophils stained by substrateless DAB reaction was measured in the successive segments and the successive layers of rat digestive tract using a semiautomatic computerized image analysis system. The results were calculated in a dual way: per area of the entire layer and per area of its connective tissue compartment, in which the eosinophils were located (extremely small number of intraepithelial and intramuscular eosinophils was not included in the analysis). The density of eosinophils in the successive segments of the digestive tract seemed to depend primarily on the time of contact between the contents and the wall of the segment, being the highest in regions of food/content retention (fundus of the stomach, cecum) and the lowest in regions of rapid passage (esophagus, pylorus, duodenum). When eosinophil density in the successive layers was compared, its gradual decrease in the successive layers (villi>lamina propria>submucosa>muscularis) was observed in almost the entire small intestine and lower values in submucosa compared to mucosa were also evident in the stomach, duodenum and small intestine. It seems that there is a decreasing gradient of chemoattractants for eosinophils dependent of the distance from the lumen and the contents of the digestive tract. However, this decreasing pattern appeared only when the density was calculated for the area of the connective tissue compartment suggesting that this method of calculation more reliably reflects the distribution of eosinophils and should be used in future quantitative studies on tissue eosinophils.