Defensins are a family of microbicidal peptides abundant in the granul
es of mammalian neutrophils, in rabbit alveolar macrophages, and in hu
man and murine intestinal Paneth cells. We cloned and sequenced the ge
nes of three neutrophil-specific defensins. Human HNP-1 and HNP-3 are
nearly identical and rabbit NP-3a is closely related. The four known n
eutrophil-specific defensin genes are strikingly similar in the struct
ure and organization of their three exons and two introns, but the thr
ee defensin genes expressed in macrophages (MCP-1 and -2) or Paneth ce
lls (HD-5) are organized differently: HD-5 has only two exons, and MCP
-1 and -2 have a comparatively short first intron. The diverse genomic
organization of defensin genes may contribute to their cell-specific
expression.