Preproenkephalin, is a Th2 cytokine but is not required for Th2 differentiation in vitro

Preproenkephalin (PPNK) mRNA expression has been detected in many cells of the immune system, including monocytes and lymphocytes. In the present pape r. the expression of PPNK mRNA in purified CD4(+) Th1 and Th2 lymphocyte su bpopulations is investigated and correlated with the presence of the opioid neuropeptides leu- and met-enkephalin. We found that PPNK mRNA and met-enk ephalin were present at higher levels in the Th2 cultures compared with the Th1 cultures. Lymphocytes from PPNK-deficient mice were then used to look at the role of PPNK in Th2 lymphocyte differentiation. Lymphocytes from the se mice could be driven into a Th2 phenotype, suggesting that cultures cont aining IL-4 do not require PPNK for Th2 differentiation.