IL-7 is a hematopoietic growth factor that primarily affects early B and T cells. Produced by thymic stromal cells, spleen cells and keratinocytes, IL-7 can also co-stimulate the proliferation of mature T cells in combination with other factors, such as ConA and IL-2. Human and murine IL-7 are cross-species reactive. Recombinant Human IL-7 is a 17.5 kDa protein containing 153 amino acid residues.