Kinetic analysis of microchimerism induced by intrathymic injection of allogeneic splenocytes in mice

Allograft survival facilitated by intrathymic (i.t.) injection of allogenei c cells have shown that modifications of T-cell development induce specific tolerance. One hypothesis is that the resulting microchimerism may play a role in preparing the host immune system for the allograft. To investigate whether the deliberate introduction of allogeneic splenocytes into the thym us of adult mice allows the establishment of a lasting donor/recipient micr ochimerism, a full allogeneic mouse system (H-2 and Mis) with additional se x mismatch was used. Male cells injected into female mice were detected usi ng an optimized nested-polymerase chain reaction which specifically amplifi es the SRY gene with a sensitivity of 1/10(4). After i.t. injection, donor cells were observed early both in the lymph nodes and spleen (75 and 25% of mice, respectively). They were still present on day 6, although preferenti ally in the thymus (100% of mice) than in the lymph nodes (50% of mice) or in the spleen (22% of mice). After intraperitoneal (i.p.) or subcutaneous ( s.c.) injection, donor cells were early (2 h) but transiently detected in t he thymus, since on day 6 they were detected in 0 and 17% of mice after i.p . and s.c. injection, respectively. Kinetics of donor-cell detection was si milar both in the spleen and lymph nodes with a clear decrease in the perce ntage of mice with donor-cell detection between day 2 and day 6 (20 and 17% of positive mice for the spleen after i.p. and s.c. injections, respective ly - 20 and 33% of positive mice for the lymph nodes after i.p. and s.c. in jections, respectively). Our results clearly show that i.t. injection of al logeneic splenocytes induces a microchimerism which is both more lasting an d detected in a higher percentage of mice than by the i.p. and s.c, routes, both at the central (thymus) and peripheral (spleen) levels. (C) 2000 Else vier Science B.V. All rights reserved.