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INCREASED SENSITIVITY OF IN VIVO MARROW‐THYMUS INTERACTION ASSAYS IN MICE

Bone marrow-thymus reconstitution assays in lethally irradiated host mice can be increased in sensitivity by at least a factor of 10 by allowing a delay between bone marrow protection on the day of lethal irradiation and thymus cell injection plus antigen challenge. Compared to using no delay, a 4-day delay in CBA mice with sheep erythrocytes as antigen resulted in a 10–30-fold increase in antibody-forming cells (AFC)/spleen. There was no significant rise in AFC/spleen in bone marrow-protected controls not given thymus cells during this time. Both horse and sheep erythrocytes gave an increased response with a delay. Neonatally and adult thymectomized mice used as recipients also showed increased sensitivity with a delay. Double transfer experiments indicate that the effect of the delay probably is not proliferation of precursor cells.