Sentence:  Homozygous and heterozygous * * f cells , * * f and homozygous and heterozygous * * f cells were <WSD>used</WSD> to test each sample ; however , in the interest of clarity and conciseness only the results obtained with homozygous * * f and homozygous * * f cells will be presented here . 
Meaning of the word marked with <WSD> tags:  put into service; make work or employ for a particular purpose or for its inherent or natural purpose