Evidence for a mutual influence of idiotype-expressing donor cells and recipient lymphocytes in neonatal hosts

Nonirradiated recipients do not permit activation of transferred syngeneic lymphocytes. This transplantation barrier gives us insight into the mechanism of the regulatory circuits of the donor's and host's immune network. The present report demonstrates that this barrier depends on the state of differentiation of cells from both donor and host. We measured the expression of anti-alpha (1-3)dextran (Dex) correlated idiotypes by cells from responder BALB/c animals (allotype IgHa, Dex+, IdDex+) in nonresponder (IgHb, Dex-, IdDex-) congeneic mice. Adult IgHb recipients did not permit activation of either adult spleen or bone marrow cells (isogeneic barrier). Neonatal recipients showed functional tolerance towards adult spleen cells. By contrast, neonates neither permitted activation of adult B cell-depleted bone marrow cells, nor of neonatal immature spleen cells. The results show that the immature system of the neonate is permissive towards mature (adult) congeneic lymphocytes, but not towards immature cells from congeneic neonates or adult bone marrow. It appears that mature adult cell populations are dominant in the immature neonatal host. However, the time required by transferred immature cells to differentiate in the neonatal recipient concomitantly allow the latter to gain maturity and functionally reject the grafted cells.