Development, growth, and maintenance of hematopoietic cells in the fetal liver or lymphocytes in the thymus are regulated various kinds of cellular interaction molecules. To investigate these molecules, we developed novel co-culture methods, i.e, co-culturing fetal liver adherent cells and non-adherent cells. Applying this method, we established a novel mAb detecting CD13 molecule on the fetal liver adherent cells. CD13 is also acting on the development of fetal thymocytes. On the other hand, we identified that saposin, a molecule regulating sphingomyelin metabolism, is acting as a growth factor of immature thymocytes.
(1) A novel mAb, Ndk-10, inhibited the c-kit+ cell proliferation in the fetal liver. Amino acid sequence study revealed that the Ndk-10 reacts with CD 13.
(2) CD13 is also expressed in the early thymus and thymic medullary epithelial cells of adult mice. CD13 expression was enhanced by the addition of IL-4.
(3) Ndk-10 (anti-CD13) also inhibited c-kit+ cell proliferation in the fetal liver organ culture system.
(4) We purified immature thymocyte growth factor from Con-A stimulated splenocyte culture, and its partial amino acid sequence was found to be identical to that of saposin.