<p>Interleukin-7 (IL-7) [<cite idref="PUB00002018"/>] is a cytokine that serves as a growth factor for early lymphoid cells of both B- and T-cell lineages. Interleukin-9 (IL-9) [<cite idref="PUB00003177"/>] is a cytokine that supports IL-2 independent and IL-4 independent growth of helper T-cells. </p><p>Interleukin-7 and -9 seems to be evolutionary related [<cite idref="PUB00015241"/>]. As a signature pattern, we selected a conserved region located in the C-terminal section of the protein. </p>