Ontogeny of human cell-mediated immunity: age-related variation of in vitro infantile lymphocyte transformation.

Thymidine uptake of unstimulated and of phytohemagglutinin (PHA)-, streptokinase-streptodornase (SK-SD)- and candida extract (candida)-stimulated lymphocytes of normal infants less than 20 months old was evaluated. Thymidine uptake of unstimulated and PHA-stimulated young infants' lymphocytes was avid, resembling that of newborn cells. Over periods of weeks to months, infantile lymphocytes demonstrated transition in unstimulated and PHA-induced thymidine uptake from response patterns like cord blood cells to ones more characteristic of adult lymphocytes. Candida- and SK-SD-induced thymidine uptake of lymphocytes from very young infants was likewise apparently quite avid, resembling cord blood cells. However, factoring out high unstimulated thymidine uptake by conversion of data to stimulation indexes clarified differing paces of acquisition of transformation responsiveness of the two naturally acquired infectious antigens. Specific lymphocytes reactivity to SK-SD was quite low in all groups of infants compared with candida-induced transformation, which in some infants acquired adult proportions.