YOLK SAC-DERIVED MURINE MACROPHAGE CELL-LINE HAS A COUNTERPART DURINGES CELL-DIFFERENTIATION

Macrophages are phagocytic hematopoietic cells involved in several imm une processes, but they are also present early in mammalian developmen t and may participate in embryonic tissue remodeling. We have isolated and characterized a cell line, Py-YSA, from the mouse yolk sac. Py-YS A cells have several functional properties of macrophages, including u ptake of acetylated low density lipoprotein and phagocytic capability They express the murine macrophage markers F4/80 and Mac-1, and they e xpress RNA for the c-fms receptor Their expansion in culture requires fibroblast conditioned medium or exogenous monocyte-colony stimulating factor. Murine ES (embryonic stem) cell cultures that undergo in vitr o differentiation recapitulate yolk sac development, and during this p rocess cells arise that express both Mac-1 and F4/80 and morphological ly resemble the Py-YSA cells. The kinetics and distribution pattern of the Mac-1+ cells during a time course of ES cell differentiation sugg est that they originate in the blood islands, and that they subsequent ly leave the blood islands and disperse to tissue sites. Both F4/80 an d Mac-1 are first expressed in primary cultures from day 9.5 yolk sacs . The PS-YSA cultured cells thus resemble embryonic tissue macrophages by several criteria, and they share a marker profile with a cell type found in yolk sacs and differentiating ES cells. Py-YSA cells will be a useful reagent for further understanding: the role of embryonic tis sue macrophages in development. (C) 1997 Wiley-Liss, Inc.