Human keratinocytes lack the components to produce leukotriene B-4

The cellular origin of leukotriene B-4 (LTB(4)), a potent pro-inflammatory molecule present in psoriatic lesions, has yet to be determined, In the present study, cultured human keratinocytes were evaluated for their ability to produce LTB(4). Keratinocytes stimulated under a variety of conditions did not produce detectable amounts of LTB(4), as measured by enzyme immunoassay and liquid chromatographic techniques, Prostaglandin E(2) and 15-hydroxyeicosatetraenoic acid were the only eicosanoids detected, The capacity of keratinocytes to synthesize 5-lipoxygenase (5-LO) products, or lack thereof, was further evaluated by preparing subcellular fractions and examining them for the presence of 5-LO activity and the proteins responsible for LTB(4) production. Using Western blot analysis, we detected no bands that migrated with the 78-kDa 5-LO enzyme, Subcellular fractions were also examined for the presence of the 5-LO-activating protein (FLAP). This protein, which is essential to 5-LO activity, could not be detected in any keratinocyte preparation examined. Consistent with the absence of proteins, the mRNAs for 5-LO and FLAP were undetectable by reverse transcriptase polymerase chain reaction analysis, These results demonstrate that human keratinocytes lack the crucial proteins necessary for LTB(4) production.