I switched institutions recently and saw that, in the new facility, the BD Fortessa gives two lymphocyte populations in SSC vs FSC. See the attached plot.
At the previous institution, I used very similar samples on a BD Fortessa and two BD Symphony but never saw something like it.
The cells are not different in viability and subsets such as T cells, B cells, or NK cells (CD3, CD19, CD56) are not enriched in one or the other population.
Therefore, I think that this could be a technical issue. It is very reproducible in different samples and across different measurements (spread out over two weeks, CST run inbetween etc.)
Has anyone seen this? How can we fix it?
/edit: these are human PBMC.
Freshly isolated (non-activated).
We see no changes against time.
The two populations don‘t differ in viability (we use a fixable viability dye).
The PBMC are fixed with BD Cytofix (4.2% PFA) for 20 min at 4 degrees.