Rhesus monkey (Macaca mulatta) mucosal antimicrobial peptides are close homologues of human molecules

Abstract

One component of host defense at mucosal surfaces appears to be epithelium-derived antimicrobial peptides. Molecules of the defensin and cathelicidin families have been studied in several species, including human and mouse. We describe in this report the identification and characterization of rhesus monkey homologues of human mucosal antimicrobial peptides. Using reverse transcriptase PCR methodology, we cloned the cDNAs of rhesus monkey beta-defensin 1 and 2 (rhBD-1 and rhBD-2) and rhesus monkey LL-37/CAP-18 (rhLL-37/rhCAP-18). The predicted amino acid sequences showed a high degree of homology to the human molecules. The expression of the monkey antimicrobial peptides was analyzed using immunohistochemistry with three polyclonal antibodies to the human molecules. As in humans, rhesus monkey antimicrobial peptides are expressed in epithelia of various organs. The present study demonstrates that beta-defensins and cathelicidins of rhesus monkeys are close homologues to the human molecules and indicate that nonhuman primates represent valid model organisms to study innate immune functions.

FIG. 1

Comparison of the amino acid sequences of rhBD-1, rhBD-2, and rhLL37/rhCAP-18 with their human homologues. Rhesus monkey β-defensins reveal a high degree of similarity to the human molecules, and rhLL-37 is identical to LL-37, including the cathelin-like proregion (amino acids 31 to 131 of the LL-37 sequence). Conserved cysteines of the defensins are labeled by boxes.

FIG. 2

Immunohistochemical detection of rhesus monkey antimicrobial peptides in organs of the respiratory and gastrointestinal tract. In large airways (A, rhBD-1; B, rhBD-2; C, rhLL-37), all peptides were detected in ciliated epithelial cells. In distal lung (D, rhBD-1; E, rhBD-2; F, rhLL-37), type II pneumocytes revealed a positive signal for rhBD-2 (arrows), and alveolar macrophages were stained with antibodies to all three antimicrobial peptides. In the stomach, chief cells of the mucosa stained positive for all three peptides (G, rhBD-1; H, rhBD-2; I, rhLL-37); however, the staining pattern is specific for the peptides. Enterocytes of the small (J, rhBD-1) and large bowel (K, rhBD-1) were stained diffusely positive for the presence of the peptides. In the duodenum, cells located at the basal portion of crypts were intensely stained for rhBD-1 (J, arrow). In the subepithelial space of the intestinal mucosa, lymphocytes were stained intensely with the hBD-1 antibodies (K, arrow). A preimmune control section of colon showed no specific signal (L, rhBD-1 preimmune). The bar indicates 30 μm in panels A to F, 15 μm in panel G, and 60 μm in panels H to L. As chromogens, we used DAB (panels A to G, K, and L) or AEC (panels H, I, and J) (see Materials and Methods).

FIG. 3

Immunohistochemical detection of rhesus monkey antimicrobial peptides in kidney (A, rhBD-1; B, rhBD-1 preimmune; C, rhLL-37) and conjunctival tissue of the eye (D, rhBD-1; E, rhBD-2; F, rhLL-37). The bar indicates 120 μm in panels A to C and 30 μm in panels D to F. As chromogens, we used DAB (panels A, B, D, and F) or AEC to (panels C and E).