if you don't do any purification, RBC will mess up the assay. So, I believe you will remove RBC, then the dominant cells are granulocytes. You will use RNAseq? You need to be careful when performing whole blood transcriptome analysis as for different subjects, the components of different cell lineages can be different. You may need to use the reference blood lineage RNAseq data published in Nature last year.

I agree with JInsong Qiu. As there are very few factors which are exclusively produced by one specific subset, the only message you would obtain is that you have a response which is dominated by xyz and could be a result of increased production by....

I  am looking at  the whole blood microarray datasets available in open source like GEO or Array express and I am not performing any experiments. For the  considered datasets, they have used PAXgene Blood RNA Kit for RNA isolation and purification.I have read in few papers  where PAX gene efficiently  removes globin and other cell types and retain only leukocytes.Is it ok to consider ??