Distribution of gastointestinally absorbed⁵⁹Fe. (A) Control B6 (▧) and β2m^−/−(□) mice received a radioactive test dose solution of ferrous iron. At day 6, the mice were exsanguinated and their organs were dissected. The amount of radioactivity in selected organs was measured in a gamma counter. The data are presented as the mean specific activity (counts per minute per gram of wet weight of tissue) ± SD (n = 12; combined data from 2 experiments). Mean values in livers and spleens from β2m^−/− mice were significantly different from those of B6 mice (Student's t-test): P < .05. (B) Radioactivity recovered from livers, spleens, and blood versus iron retention in control B6 (•) and β2m^−/− (▵) mice from the same experiments. Iron retention was determined at day 6 in a whole-body counter. Individual values for each mouse are shown.