Presence of IL-9 in paired samples of human colostrum and transitional milk

Background: Human colostrum and breast milk are known to contain high levels of cytokines, cytokine receptors, and chemokines. Objective: To investigate the presence and compare levels of soluble cytokines in paired samples of human colostrum and milk. Methods: Levels of 27 cytokines were measured in 9 paired samples of human colostrum (day 2 after delivery) and breast milk (day 4 or 5 after delivery) by using multiplex technology. Results: The majority of cytokines and chemokines investigated have been previously described in colostrum and/or breast milk. For the first time, we describe the presence of IL-9 in both human colostrum and milk. Of the 27 cytokines investigated, only IL-5 was absent in both colostrum and milk, whereas IL-1β, IL-2, IL-4, IL-15, IL-17, and MIP-1α were present in colostrum, but not in breast milk. In general, colostrum contained higher concentrations of cytokines with respect to human milk. Conclusion: Our data confirm and expand previous studies showing that human colostrum and breast milk are rich in cytokines and chemokines, including IL-9, which might contribute to the development of the immune system of the newborn.