PHENOTYPIC AND FUNCTIONAL-CHARACTERIZATION OF LONG-LIVED NK CELL-LINES OF DIFFERENT MATURATIONAL STATUS OBTAINED FROM MOUSE FETAL LIVER

Culture of day 14 mouse fetal liver (FL) cells in high dose IL-2, toge ther with appropriate combinations of IL-4 and PMA, resulted in the ge neration of cell lines, termed FL-A lines, that were phenotypically an d functionally indistinguishable from cultured adult splenic NK cell p opulations with the single important exception that no Ly49-expressing cells were present. By contrast, when FL cells were cultured in low-d ose IL-2 alone, a second population of slow-growing NK-like cells, ter med FL-B cells, emerged. These cells expressed the NK markers asialoGM 1, 10A7, 2B4, and Fc gamma RII/III but differed from FL-A and splenic NK cells in expressing IL-2R alpha and stem cell factor receptor (SCFR ) but no B220. Most lines derived in this manner had minimal or no cyt olytic activity and only very low levels of NK1.1. However, they could secrete substantial quantities of several lymphokines including IL-3, granulocyte-macrophage (CM)-CSF, TNF-alpha; and, most surprisingly, I L-2. A minority of FL-B lines, typified by line 903, displayed marked cytolytic activity, moderate levels of NK1.1, reduced production of IL -2, and the capacity for accelerated growth in high-dose IL-2. FL-B li nes generally expressed mRNA for CD3 gamma but not for other CD3 chain s, whereas FL-A and fetal thymic (FT) NK lines often expressed mRNA fo r all four CD3 chains. Despite many similarities to pro-T cells, FL-B cells showed no capacity to differentiate into mature T cells. Taken t ogether, our results suggest that NK lines of different maturity can b e obtained from fetal liver, with FL-B lines being the most immature, FL-A lines the most mature, and lines such as FL-B 903 representing an intermediate state of differentiation.