Ontogeny of circulating B lymphocytes in neonatal calves

The ontogeny of lymphocytes bearing surface immunoglobulin (B lymphocytes) in the peripheral blood of neonatal and young calves was determined by fluorescent antibody techniques in calves from one day to 140 days old. The percentage of B lymphocytes in neonatal calves (less than one week) was approximately 5% of the total mononuclear cell population. B lymphocytes increased steadily in the peripheral blood of calves until 20 weeks of age when values stabilised (approximately 19%) and were similar to adult levels.