The appearance of immunological competence at an early age in New Zealand black mice.

Adult and 5-day-old New Zealand Black (NZB) and Ju control strain mice were injected with sheep red blood cells. At various times after injection they were killed and the spleens, lymph nodes and thymus tested for haemolysin-producing cells. When the response was expressed as plaque-forming cells (PFC) per million viable cells, the response curve of the spleens of baby NZB mice was very similar to the response in the spleens of the adults, and the response in the lymph nodes of the babies was as high and more sustained than that of the adults. In Ju control strain baby mice of this age, the response in the spleen and the lymph nodes was both reduced and delayed compared with the adults. Neither strain gave a significant response in the thymus. The spleen and lymph nodes of adult NZB mice showed a response which was delayed but not reduced as compared with the adults of the Ju control strain, whereas in baby NZB mice the spleen and lymph nodes showed a response which was advanced and increased (particularly in the lymph nodes) compared with control strain babies (Ju, Swiss, C57B1, CBA). The NZB mice did not reach this level of responsiveness until they were 4–5 days old.