What kind of sample are you talking about? If it is a solid tissue, you could do IHC/IF. Stain the cells with antibodies directed against NK cell markers and then do microscopy.

Dear Julie Joseph...

Thanks for your interest..concerning blood sample...do you have a protocol?

It will depend of the markers you want to evaluate. Even with blood you could use a IHC assay as Julie suggest. Also you could consider western blot but I guess you will need to isolate the cellular membrane first. A other assay to consider is ELISA.

Dear Oliver Lucar..

Thanks for your valuable answer...concerning using ELISA..can you just give me some clues..regards

If working with blood, your options are limited. You could do blood smears and try Wright-Giemsa staining to look at NK cells. See the links below for the protocol and an example of a blood smear.

https://assets.thermofisher.com/TFS-Assets/APD/manuals/IS89013-Wright-Giemsa-Stain-Solutions.pdf

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If you don't need to count NK cells and only need to see the expression of NK cell markers, you could do Western Blots or ELISA as Olivier Lucar mentioned, but only if you have primary/secondary antibodies against the markers you are interested in. You could find protocols online on how to perform these two techniques.

Dear Julie Joseph...

Thanks for your answer..yes,my sample is blood...what is your suggestion for replacing blood sample with other specimen...?

If you want to go with Elisa you should first isolated NK cells from the blood. Then it will depend of what markers you want to evaluate

Could you please give details on what your objective is and what your experimental strategy is? This way, I can narrow down your options and suggest something that is suitable for you.

Dear julie Joseph..thanks for your interest... the proposal goal is to estimate NK cells in blood samples of patients with high internal DU concentration ..

OK. From your answer, seems you want to enumerate NK cells in circulation and so western blot and ELISA are out. Your only options would be flow cytometry or blood smears. Since you said you want an alternate to flow cytometry, you are left with preparing blood smears, staining them with Wright Giemsa and then microscopy.