Cathelicidins are precursors of defense peptides of the
innate immunity and are widespread in mammals. Their structure
comprises a conserved prepropiece and an antimicrobial domain
that is structurally varied both intra- and inter-species. We
investigated the complexity of the cathelicidin family in horse by
a reverse transcription-PCR-based cloning strategy of myeloid
mRNA and by Southern and Western analyses. Three novel
cathelicidin sequences were deduced from bone marrow mRNA
and designated equine cathelicidins eCATH-1, eCATH-2 and
eCATH-3. Putative antimicrobial domains of 26, 27 and
40 residues with no significant sequence homology to other
peptides were inferred at the C-terminus of the sequences.
Southern analysis of genomic DNA using a probe based on the
cathelicidin-conserved propiece revealed a polymorphic DNA
region with several hybridization-positive fragments and suggested
the presence of additional genes. A null eCATH-1 allele
was also demonstrated with a frequency of 0.71 in the horse
population analyzed and low amounts of eCATH-1-specific
mRNA were found in myeloid cells of gene-positive animals. A
Western analysis using antibodies to synthetic eCATH peptides
revealed the presence of eCATH-2 and eCATH-3 propeptides,
but not of eCATH-1-related polypeptides, in horse neutrophil
granules and in the secretions of phorbol myristate acetatestimulated
neutrophils. These results thus suggest that eCATH-2
and eCATH-3 are functional genes, whereas eCATH-1 is unable
to encode a polypeptide.
