A PORCINE TROPHOBLAST CELL-LINE THAT SECRETES GROWTH-FACTORS WHICH STIMULATE PORCINE MACROPHAGES

We have previously described experiments in both the mouse and the hum an indicating that cytokines capable of activating macrophages (colony -stimulating factor-1 [CSF-1], granulocyte-macrophage colony-stimulati ng factor [GM-CSF], and interleukin-3 [IL-3]) are produced by, and/or stimulatory of, trophoblast cells in these species. In contrast to the complex hemochorial placenta of the mouse and humans, the pig has a s imple diffuse type of placenta, designated as epitheliochorial. To det ermine whether similar phenomena might not apply to the porcine pregna ncy, we have isolated a cell line, designated Jag-1, from the trophobl astic tips of Day 14 porcine embryos. We report here that this cell li ne is cytokeratin-positive, vimentin-negative, and therefore of epider mal origin. It also shares various morphological characteristics with porcine trophoblast as demonstrated at both the light and electron mic roscopic levels. In addition, Jag-1 cells and primary trophoblast tiss ue from Day 14 blastocyst do not express classical major histocompatib ility (MHC) class I and class II antigens, a unique feature of trophob last in many species. To determine the ability of this cell line to pr oduce cytokines, we have developed an assay for porcine macrophage gro wth factors that utilizes uptake of tritiated thymidine. This assay re sponds positively to recombinant bovine GM-CSF and, more importantly, detects a similar activity in supernatants of the porcine trophoblast cell line and of Day 14 blastocysts. Thus porcine trophoblast cells, l ike their murine and human counterparts, produce and potentially inter act with lymphohematopoietic cytokines that are traditionally associat ed with macrophages.