Developmental changes of components of the red cell immune system in the rabbit

Red cell immune adherence (RCIA) occurs not only in primates but also in nonprimates such as the rabbit. We utilized the rabbit as an animal model to study developmental changes in the immune functions of rabbit red cells. Significant differences between adult and newborn rabbits were found. RCIA-receptor activity of the newborn rabbits was significantly larger than that of adult rabbits (p less than 0.0005). Serum RCIA inhibiting factor, which completely prevented any detectable RCIA, was evident in about 40% of adult but not in any of the newborn rabbits (p less than 0.01). RCIA-inhibiting factor was also detectable in three out of eight pregnant rabbits but did not cross the placenta into the rabbit fetus. High concentrations (33%-100%) of most adult sera but not of newborn sera inhibited RCIA (p less than 0.001). It is suggested that, like the thymus, red cell immune function may reach its peak activity during early developmental periods. The red cell immune function may be essential for the removal of antigen-antibody complement complexes from the fetal circulation and may participate in the activation of T suppressor cells which adhere to autologous red cells.