Hello everyone. I performed immunofluorescence staining to characterize MSCs that I isolated from the placenta. As expected, the results were CD90+, MHC-, and SOX2+. However, CD45, which should be negative, came out positive. The same thing happened in my previous isolation. Additionally, in another cell study, CD45 came out positive even though it should have been negative. Can CD45+ MSCs exist? Are we doing something wrong, or is the problem with the CD marker we are using? Thanks in advance.
In my experience, anything can exist, but the question is whether it exists outside the context of your experiment. CD45 is generally a good marker of immune cells, and so one shouldn't expect to find it on MSCs. So you need to think about what could make your cells CD45 positive if they aren't really CD45 positive:
1. Are you certain that your antibody is specific for CD45? Have other groups used this same antibody for staining of MSCs and shown that it doesn't bind?
2. What are you using to decide that your cells are positive? Do you have an isotype control with the same fluorophore that shows lower binding. Some antibodies/fluorophores will bind non-specifically to certain cell types, so you cannot say a cell is positive because the antibody doesn't bind as much to a different cell type.
3. Do you have CD45+ cells (immune cells) mixed in with your MSCs. A possibility (although perhaps unlikely) is that trogocytosis could then explain why your MSCs become CD45+. If two cells interact, there can be a transfer of membrane between the cells, which can lead to protein expression on a cell that does not itself express the mRNA for the protein.
4. Has anybody else looked at MSCs in the placenta? Perhaps you find a strange CD45+ MSC population there?
Hi, I recently encountered the same problem. I isolated TER119-CD45-CD31- MSCs through magnetic beads sorting for cell culturing. At passage 1-2, the cells were collected for flow characterization, and it turned out that most of the cultured cells were CD45+. Could MSC expression of CD45 be up-regulated upon culturing?
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