Immunoglobulin-bearing lymphocytes: their demonstration in adult sheep and ontogeny in the sheep fetus.

A method for the preparation of lymphocytes from sheep blood is described. Lymphocytes from adult and fetal sheep have been examined by immunofluorescence for surface immunoglobulin (sIg) determinants. Young adults (1.5 years) had a mean of 23.2% sIg cells, older adults (8.75 years) a mean of 9.7% sIg cells. Pregnancy did not influence these values. The earliest lymphocytes with sIg in fetal lambs were demonstrable at 52 days (96 mm crown-rump length) and countable by 56 days (110 mm CRL) at 0.3% sIg. The percentage rose rapidly to 15.1% between 78 and 87 days, followed by a fall to 2.1% around 117 days with a second increase thereafter. The significance of this spontaneous appearance of fetal sIg cells is discussed.