Comment: Response to an article by Hamilton et al. on 'Effects of colony stimulating factor-1 on human extravillous trophoblast growth and invasion'

Abstract

We wish to comment on the article by Hamilton et al. 1998. Table 1 shows the similarities and differences between the observations made in the two papers (Lewis et al. 1996, Hamilton et al. 1998) which have investigated the roles of colony-stimulating factor-1 (CSF-1) and its receptor (c-fms) in human extravillous cytotrophoblast (EVCT). Both types of EVCT show the components of a CSF-1/ c-fms autocrine loop, and it is clear that there is no role for CSF-1 in controlling EVCT invasion (Table 1). However, in primary cells (designated EVT), CSF-1 was a positive regulator of cell proliferation (Hamilton et al. 1998), whereas in immortalised TCL-1 cells (and in BeWo choriocarcinoma) CSF-1 appeared to be an inhibitor of such proliferation (Lewis et al. 1996). There are a number of factors which may contribute to this difference in the data obtained, but we must firstly point out that Hamilton et al. have not reported our previous data accurately. In the last paragraph of the discussion they state ‘‘. . . those cells (TCL-1 cells) also exhibited an autocrine CSF-1 loop which enhanced proliferation.’’ This is the opposite of what we reported (Lewis et al. 1996), that ‘‘Proliferation of TCL-1 cells . . . . was elevated in response to treatment with a CSF-1 neutralising antibody.’’ (abstract). We therefore suggested that CSF-1 may be a differentiation or maturation factor which suppresses the proliferation of trophoblasts (Aplin 1991). Possible explanations for the differences in effects of CSF-1 include the following: (1) EVT were obtained by culture of adherent cells and explants from minced first trimester villi (Hamilton et al. 1998), whereas TCL-1 were from chorionic membranes and immortalised with the SV40 large-T antigen (Lewis et al. 1996). There may be a change in trophoblast response to CSF-1 depending on gestational age, intrauterine location or, as described by Hamilton et al., the fact that TCL-1 were immortalised. (2) TCL-1 cells did not respond to CSF-1, and the levels of CSF-1 released were sufficient to saturate the c-fms receptor (Lewis et al. 1996). The release of CSF-1 from EVT cells was not quantified, but the response of the cells to CSF-1 in vitro suggested that the receptor would not be saturated. The quantity of CSF-1 needed (62·5 ng/ml, or 2750 nM) is higher than the accepted affinity of the c-fms receptor (230 nM). (3) The proliferation indices of the cells seem to differ markedly. In serum-free medium, EVT incorporated 400–1000 c.p.m./6 h (Hamilton et al. 1998). TCL-1 cells incorporated about 300 000 dpm/h (our unpublished data), a rate substantially greater. The EVT cells were examined on day 5 of culture, in contrast to TCL-1 cells