I conducted experiments with neutrophils isolated from bone marrow using density gradient centrifugation, referring to this literature (DOI: 10.1002/0471142735.im0320s110). You can either prepare separation solutions of different densities using percoll yourself or purchase 1119 and 1077 from sigma to isolate neutrophils. However, I have not isolated cells from the placenta. You can refer to some digestion methods, such as adding trypsin or collagenase 4 and DNase, to prepare a cell suspension first.

As noted above, isolation can be accomplished. A Percoll gradient should be considered following digestion, and my experience is with type 4 collagenase and DNase to digest organs. Proteases have the potential to strip membrane antigens, confusing subsequent flow cytometry analysis. Culture is a different challenge. PMNs are terminally differentiated and don't proliferate. Further, they have a short lifespan in vitro, from hours to a few days. The placenta has been shown to have myeloid progenitors, i.e., PMN precursors, which can be cultured. Any standard culture with growth factors for hematopoietic/myelopoietic progenitors would work. I would assume it would include GM or G-CSF, and any other cytokines could be included. SCF, FLt3L, IL3 etc. Question for another discussion.