Yes, it is autofluorescence of the RBCs....a common problem in this type of work. The heme group in red blood cells exhibits broad autofluorescence due to its porphyrin ring structure.

I've never found a solution to eliminating the autofluorescence. I tend to take pictures where minimal RBCs are present. I put an arrow to them in the figure indicating RBC autofluorescence in the text. This has always been accepted by reviewers.

One solution is not to use fluorescence, ex; peroxidase labelling technique

I have had good experience with removing red cell autofluorescence with the Vector TrueView Autofluorescence Quenching Kit or using Sudan black.

Vector TrueVIEW works pretty well, though the quenching time will probably be longer than the manufacturer recommends.