Identification of collagen IV derived danger/alarm signals in insect immunity by nanoLC-FTICR MS.

The immune system can be stimulated by microbial molecules as well as by endogenously derived danger/alarm signals of host origin. Using the lepidopteran model insect Galleria mellonella, we recently discovered that fragments of collagen IV, resulting from hydrolysis by microbial metalloproteinases, represent danger/alarm signals in insects. Here, we characterized immune-stimulatory peptides generated by thermolysin-mediated degradation of collagen IV using nanospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) after separation by nanoscale liquid chromatography (nanoLC). The combination of FTICR MS analysis and de novo peptide sequencing resulted in the identification of 38 specific collagen IV fragments of which several peptides included the integrin-binding motif RGD/E known from numerous mammalian immune-related proteins. Custom-synthesized peptides corresponding either to the presently identified collagen peptide GIRGEHyp or to a well-known integrin-binding RGD peptide (GRGDS) were injected into G. mellonella to determine their immune-stimulatory activities in vivo. Both peptides stimulated immune cells and systemically the expression of lysozyme and a specific inhibitor of microbial metalloproteinases. Further examination using specific MAP kinase inhibitors indicated that MEK/ERK and p38 are involved in RGD/E-mediated immune-signaling pathways, whereas JNK seems to play only a minor role.