The antimicrobial peptide human -defensin-2 (hBD-2) produced by epidermal keratinocytes plays pivotal roles in antimicrobial defense, inflammatory dermatoses, and wound repair. hBD-2 induces histamine release from mast cells. We examined the in vitro effects of histamine on hBD-2 production in normal human keratinocytes. Histamine enhanced TNF-- or IFN--induced hBD-2 secretion and mRNA expression. Histamine alone enhanced transcriptional activities of NF-B and activator protein-1 (AP-1), and potentiated TNF--induced NF-B and AP-1 activities or IFN--induced NF-B and STAT1 activities. Antisense oligonucleotides against NF-B components p50, p65, AP-1 components c-Jun, c-Fos, or H1 antagonist pyrilamine suppressed hBD-2 production induced by histamine plus TNF- or IFN-. Antisense oligonucleotide against STAT1 only suppressed hBD-2 production induced by histamine plus IFN-. Histamine induced serine-phosphorylation of inhibitory NF-B (IB) alone or together with TNF- or IFN-. Histamine induced c-Fos mRNA expression alone or together with TNF- while did not further increase c-Jun mRNA levels enhanced by TNF-. Histamine induced serine-phosphorylation of STAT1 alone or together with IFN- while did not further enhance IFN--induced tyrosine-phosphorylation of STAT1. The histamine-induced serine-phosphorylation of STAT1 was suppressed by MEK inhibitor PD98059. These results suggest that histamine stimulates H1 receptor and potentiates TNF-- or IFN--induced hBD-2 production dependent on NF-B, AP-1, or STAT1 in human keratinocytes. Histamine may potentiate antimicrobial defense, skin inflammation, and wound repair via the induction of hBD-2.