Upon activation , T lymphocytes accumulate high levels of the neuropeptide enkephalin which correlate with high levels of proenkephalin mRNA in the cells .
upon activation , t lymphocytes accumulate high levels of the neuropeptide enkephalin which correlate with high levels of proenkephalin mrna in the cells .
O O O B-cell_type I-cell_type O O O O O B-peptide I-peptide O O O O O O B-peptide O O O O O