I am having trouble following what is being counted here. Is it just cells that seem to be devoted to fighting off foreign threats? Or all cells in a system tha

I am having trouble following what is being counted here. Is it just cells that seem to be devoted to fighting off foreign threats? Or all cells in a system that has an immunity function? For example: it counts 'blood cells'. But does that count all blood cells, or just those that fight disease like white blood cells?