Analysis of the expression of immunoglobulins throughout lactation suggests two periods of immune transfer in the tammar wallaby (Macropus eugenii)

Marsupial young are born in an under-developed state without mature immune responses. Prior to the maturation of an immune system, marsupial young are heavily reliant upon immune factors secreted in the milk to defend them against potential microbial pathogens in the environment. In this study, we identified and characterized the immunoglobulin heavy chain constant regions, light chains, polymeric Ig receptor (pIgR), J chain, neonatal Fc receptor (alpha chain) (FcRn) and the chemokine CCL28 from the model marsupial species, the tammar wallaby (Macropus eugenii). Low levels of conservation were seen in motifs in Cα and Cγ associated with receptor binding and or transcytosis, and this may have potential implications for functionality. We evaluated the expression of immunoglobulin genes in the tammar mammary gland throughout lactation and found that two periods of increased expression of immunoglobulin genes occur. These two periods coincide with the birth of the young, and with its first emergence from the pouch. This increased expression may represent a strategy for maternal immunological protection of the pouch young.