Decreased size and survival of weanling mice in litters of IL-5-/ -mice are a consequence of the IL-5 deficiency in nursing dams.

We have observed decreased size and increased mortality rates in interleukin 5 (IL-5)-deficient mice versus IL-5-heterozygous and wild-type mice and have sought to define these differences. IL-5-deficient mice nursed by IL-5 deficient mothers were notably underweight, with a high percentage of preweaning mortality. In contrast, IL-5-deficient mice nursed by IL-5-sufficient foster mothers from birth were well-developed and robust at weaning, with a relatively low percentage of preweaning mortality. Mammary tissues from IL-5-deficient females at various landmark stages throughout life were prepared for microscopic assessment. When compared with mammary tissue from normal mice, that from IL-5-deficient dams appeared to have fewer terminal end buds, less well-developed branching of the mammary ducts, and lower overall density of mammary gland structures. The molecular and cellular bases for the differences in mammary gland development in IL-5-deficient mice relative to wild-type animals remains unknown. Under consideration are the roles that IL-5 and eosinophil granulocytes (the primary cell responsive to IL-5) may have in mammary gland development.