Classification of antimicrobial peptides based on motifs in the amino acid sequence similar to that described by Boman . Antimicrobial peptides could also be grouped according to other principles. LL-37 and PR-39 belong to the cathelicidin family on the basis of their homologous propeptide. rTD-1=rhesus monkey θ-defensin 1; PR-39=cathelicidin from pig. Human β-defensin 3 (hBD-3) was identified by using bioinformatic screening procedures to search human chromosome 8p23 for the presence of sequence motifs typical of β-defensin (R Bals, unpublished data).