DDT and immunological responses. 3. Reduced anaphylaxis and mast cell population in rats fed DDT

Previous work showed that anaphylaxis, mast cell population, and tissue histamine content are reduced in guinea pigs given DDT injections. This study was intended to determine whether dietary intake of DDT causes similar effects. Rats immunized with diphtheria toxoid and fed diets containing DDT at 20 and 200 ppm levels for 31 days did not show effects on their serum antitoxin titers, but the numbers of metachromatically stained, histamine-containing mast cells in mesenteries were reduced: in the 20 ppm group by 46% and in the 200 ppm group by 61%. The severity of anaphylactic shock was also reduced in proportion to the DDT dietary levels, and, thus, the magnitude of mast cells. Apparently, daily dietary DDT intake above 2.2 mg DDT/kg of body weight alters the physiology of mast cells in the rat, and thus affects histamine-mediated reactions.