Comparative suppressive effects of anti-allotype antibodies on spleen cells of immature and adult rabbits

The suppressive effects of anti-allotype antibody on splenic lymphocytes of adult (>3 months of age) and newborn (1-week-old) rabbits were compared in vitro. An approximately 10-fold lower concentration of anti-b4 sufficed to modulate completely membrane-bound b4 immunoglobulin (Ig) when newborn cells were pulse-treated for 2 or 24 hr than when adult cells were tested. In contrast to splenic lymphocytes from adults, which regenerated most of the original proportion of b4⁺ cells in culture following treatment with up to 300 μg of anti-b4 for 24 hr (4), immature lymphocytes were susceptible to irreversible modulation of membrane-bound Ig even when lower concentrations of anti-b4 were used. However, under conditions permitting reversible modulation of membrane b4, lymphocytes of newborns regenerated the membrane product more rapidly than did adult cells. Both mature and immature splenocytes were shown to be capable of some level of b4 synthesis even in the continuing presence of anti-b4. No evidence for susceptibility to complement-mediated killing of newborn spleen cells by anti-allotypic antibodies was obtained. The observations reported here support the concept that the greater sensitivity of B lymphocytes from the newborn to succumb to irreversible suppressive effects by anti-allotype antibody plays a significant role in the restriction for induction of allotype suppression to the perinatal period.