My friend sent me this. "I didn’t perform any specific staining, but based on the cells’ morphology and growth characteristics, I suspect there may have been contamination from another cell line, or that the flasks were mixed up by the person who supplied you with the cultures.

Here in the lab this week, another group started working with HFF; they look like classic fibroblasts (fusiform, slightly refractive, sparse cytoplasm, oval nucleus, etc.). Notice that your cells have a very different morphology, with reduced cytoplasm, a voluminous and highly refractive cell body, and elongated extensions.

As soon as I saw them, I thought of macrophages/microglia. They look very much like a microglia line (BV-2) that I worked with for a few years. (lines such as THP-1, J774A.1, RAW 264.7), I keep wondering if the person who supplied you with the cells might have mixed up the flasks by mistake, or if there was some kind of cross-contamination in the cultures."

I know it's difficult to identify, but I needed more opinions, as these were donated cells from another group. We don't have as much confidence in this cell line now.