Cathelicidin LL-37 induces time-resolved release of LTB4 and TXA2 by human macrophages and triggers eicosanoid generation in vivo

In humans, LL-37 and eicosanoids are important mediators of inflammation and immune responses. Here we report that LL-37 promotes leukotriene B-4 (LTB4) and thromboxane A(2) (TXA(2)) generation by human monocyte-derived macrophages (HMDMs). LL-37 evokes calcium mobilization apparently via the P2X(7) receptor (P2X(7)R), activation of ERK1/2 and p38 MAPKs, as well as cytosolic phospholipase A(2) (cPLA(2)) and 5-lipoxygenase in HMDMs, leading to an early (1 h) release of LTB4. Similarly, TXA(2) production at an early time involved the same signaling sequence along an LL-37-P2X(7)R-cPLA(2)-cyclooxygenase-1 (COX-1) axis. However, at later (6-8 h) time points, internalized LL-37 up-regulates COX-2 expression, promoting TXA(2) production. Furthermore, intraperitoneal injection of mice with murine cathelicidin-related antimicrobial peptide (mCRAMP) induces significantly higher levels of LTB4 and TXA(2) in mouse ascites rich in macrophages. Conversely, cathelicidin-deficient (Cnlp(-/-)) mice produce much less LTB4 and TXB2 in vivo in response to TNF-alpha compared with control mice. We conclude that LL-37 elicits a biphasic release of eicosanoids in macrophages with early, Ca2+ -dependent formation of LTB4 and TXA(2) followed by a late peak of TXA(2), generated via induction of COX-2 by internalized LL-37, thus allowing eicosanoid production in a temporally controlled manner. Moreover, our findings provide evidence that LL-37 is an endogenous regulator of eicosanoid-dependent inflammatory responses in vivo.