Problem: The mixed lymphocyte reaction (MLR) between maternal and fetal lymphocytes as well as between adult children and their parents is imbalanced in bidirectional mixed lymphocyte cultures. The present investigation was aimed at examining which type of T cells has primary responsibility for this phenomenon.
Methods: Two-way mixed lymphocyte cultures between lymphocytes of five female and five male adults and five male and five female newborns against lymphocytes of their parents were performed. Unrelated adults served as the controls. Before and after 72 hr incubation the mixed leukocytes cultures (MLCs) were sorted by flow cytometry according to the surface markers CD4 and CD69 or CD8 and CD69. The single cell populations within the four resulting fractions were discriminated by fluoresence in situ hybridization (FiSH) using xy-DNA probes.
Results: Before incubation the share of CD8(+) CD69(+) cells in the MLCs between mothers and their newborn infants was significantly shifted toward the newborn cells (P < 0.01). After 72 hr incubation the CD8(+) CD69(+) ratio in the MLCs between mother and newborn cells and between adult children (male as well female) and their parents showed a significant shift of the CD8(+) CD69(+) cells toward the children's direction. All other MLCs showed a balanced cell population for all investigated cell types, both before and after incubation.
Conclusion: The imbalanced MLR between maternal and fetal lymphocytes and lymphocytes of adult children against their parents is mediated by a specific imbalance of the activation of CD8(+) but not of CD4(+) T cells.