Mammalian antimicrobial proteins, such as defensins and
cathelicidin, have stimulating effects on host leukocytes.
Cathelin-related antimicrobial peptide (CRAMP), the orthologue of
human cathelicidin/LL-37, is the sole identified murine
cathelicidin. CRAMP has been shown to have both antimicrobial and
angiogenic activities. However, whether CRAMP, like human
cathelicidin/LL-37, also exhibits a direct effect on the migration
and function of leukocytes is not known. We have observed that
CRAMP, like LL-37, was chemotactic for human monocytes, neutrophils,
macrophages, and mouse peripheral blood leukocytes. CRAMP also
induced calcium mobilization and the activation of MAPK in
monocytes. CRAMP-induced calcium flux in monocytes was desensitized
by MMK-1, an agonistic ligand specific for formyl peptide
receptor-like-1 (FPRL1), and vice versa, suggesting the use of FPRL1
by CRAMP as a receptor. Furthermore, CRAMP induced the chemotaxis of
human embryonic kidney 293 cells transfected with either FPRL1 or
mouse formyl peptide receptor-2, the mouse homologue of FPRL1, but
not by untransfected parental human embryonic kidney 293 cells,
confirming the use of FPRL1/mouse formyl peptide receptor-2 by
CRAMP. Injection of CRAMP into mouse air pouches resulted in the
recruitment predominantly of neutrophils and monocytes, indicating
that CRAMP acts as a chemotactic factor in vivo. Finally,
simultaneous administration of OVA with CRAMP to mice promoted both
humoral and cellular Ag-specific immune responses. Thus, CRAMP
functions as both a chemoattractant for phagocytic leukocytes and an
enhancer of adaptive immune response.
Kurosaka et al. J Immunol. 2005 May 15;174(10):6257-65.
Stimulation and cross-desensitization of Ca2+ flux in monocytes by CRAMP. Ca2+ flux of fura 2-loaded human monocytes in response to MMK-1 (A) and CRAMP (B) was measured by recording the ratio of emission at 510 after simultaneous excitation at 340 and 380. Cross-desensitization of Ca2+ flux was determined by sequential addition of MMK-1 and CRAMP at the indicated concentrations and for the indicated time periods (C) or vice versa (D). Kurosaka K,, et al. J Immunol. 2005 May 15;174(10):6257-65.
CRAMP usage of FPRL1 or mFPR2 to mediate chemotaxis. The migration of FPRL1/HEK293 (A) and mFPR2/HEK293 (B) cells in response to CRAMP or W peptide (positive control) was examined, and the average cell migration (mean ± SD) of triplicate wells was determined. CRAMP did not induce the migration of parental HEK293 cells or HEK293 cells expressing several other chemokine receptors (data not shown).
Kurosaka et al. J Immunol. 2005 May 15;174(10):6257-65.
