METHODS

Preparation of cells. Male albino rats (200-400 g) of the Wistar strain were anesthetized with ether and exsanguinated. A section of midline abdominal skin was excised, and 8-10 ml of buffered isotonic salt solution (composition below) was injected through the abdominal wall. After gentle massage of the abdomen for 90 set, a suspension of peritoneal cells was aspirated through a midline incision. Additional salt solution (8-10 ml) was injected through the diaphragm into the pleural cavity, the thorax massaged for 90 set, and the midline incision extended through the sternum to allow removal of a suspension of pleural cells. Suspensions of pleural and peritoneal cells from 4-8 rats were pooled for each experiment. The cells were centrifuged at 200 X g for 10 min and resuspended in a medium (pH 6.8-7.0) containing 150 rnM NaCl, 2.7 mM KCl, 0.9 mM CaC12, 3 mM NazHPOd, 3.5 mM KH2P04, 5.6 rnM dextrose, and 0.1% human serum albumin(fraction V, Nutritional Biochemicals). In a few experiments suspensions of washed pleural and peritoneal cells were used. In most experiments, however, the mast cells were isolated by centrifugation through solutions of Ficoll (Pharmacia) by a modification(14) of a procedure described by UvnZs and Thon (33).