The detection of mature T‐ and B‐cells during development of the lymphoid tissues of the tammar wallaby (Macropus eugenii)

The distribution of T‐ and B‐cells in the developing lymphoid and immunohaematopoietic tissues of the tammar wallaby were investigated using antibodies to the mature cell surface markers, CD3, CD5 and CD79b. In the thymus, CD3‐ and CD5‐positive T‐cells were first observed at day 12 postpartum whilst rare B‐cells were first detected at day 23. Both T‐ and B‐lymphocytes were first stained on day 21 postpartum in the spleen and day 24 in lymph nodes. In one sample from a 7‐day‐old animal, rare CD79b‐positive (CD79b+) lymphocytes were observed in the gut‐associated lymphoid tissues. However, CD3+ cells were not apparent until day 12 and CD5+ cells were not detected until day 74 postpartum. No lymphocytes were detected in liver or bone marrow samples and no bronchus‐associated lymphoid tissues were observed. The pattern of development and the distribution of T‐ and B‐cells in the lymphoid and immunohaematopoietic tissues were similar to those observed in eutherian mammals and in limited studies of other metatherians. However, the detection of apparently mature T‐ and B‐cells in the thymus and gut‐associated lymphoid tissues (GALT) at the same postnatal age highlights the need for a more substantial study of the development of GALT. This is, at present, limited by availability of marsupial‐specific antibodies.