The absence of IL-4 does not lead to a loss of male offspring in B6 mice. (a) Schema of experiment: 6- to 8-week-old B6 or B6-4KO females were mated twice with B6-4KO males. The numbers of male and female pups born in each litter were recorded. Three months after the first mating, the mice were killed and their spleen cells were assayed in vitro for anti-H-Y and anti-alloantigen reactivity. (b) The experimental data: y-axis, fraction of males born per litter; x-axis, mother's strain. Nine of 11 B6 and 11 of 12 B6-4KO mothers are represented because the litters of the other mice were eaten at birth. Each symbol represents one litter born to a B6 (circle) or B6-4KO (triangle) mother. Grey symbols, first litters; black symbols, second litters. Arrows point to litters born to mothers H-Y-sensitized by pregnancy.