Intestinal absorption of maternal leucocytes by newborn lambs.

Fluorescein isothiocyanate (FITC)-labelled maternal colostral or peripheral blood leucocytes appeared in the blood of newborn lambs following oral administration. A small population of autofluorescent cells was found in the blood of control lambs, but lambs receiving labelled leucocytes had significantly higher numbers of fluorescent cells in their blood. The peak appearance of labelled cells in the blood of newborn lambs occurred between 6 and 12 h after ingestion. Labelled cells were also absorbed by 3-day-old lambs. Cells from unrelated ewes were absorbed as well as cells from natural mothers.