Leukocyte integrin Mac-1 (CD11b/CD18, αMβ2, CR3) acts as a functional receptor for platelet factor 4

Abstract

Platelet factor 4 (PF4) is one of the most abundant cationic proteins secreted from α-granules of activated platelets. Based on its structure, PF4 was assigned to the CXC family of chemokines and has been shown to have numerous effects on myeloid leukocytes. However, the receptor for PF4 remains unknown. Here, we demonstrate that PF4 induces leukocyte responses through the integrin Mac-1 (αβ, CD11b/CD18). Human neutrophils, monocytes, U937 monocytic and HEK293 cells expressing Mac-1 strongly adhered to immobilized PF4 in a concentration-dependent manner. The cell adhesion was partially blocked by anti-Mac-1 mAb and inhibition was enhanced when anti-Mac-1 antibodies were combined with glycosaminoglycans, suggesting that cell-surface proteoglycans act cooperatively with Mac-1. PF4 also induced Mac-1-dependent migration of human neutrophils and murine WT, but not Mac-1-deficient macrophages. Coating of bacteria or latex beads with PF4 enhanced their phagocytosis by macrophages by ∼4-fold, and this process was blocked by different Mac-1 antagonists. Furthermore, PF4 potentiated phagocytosis by WT, but not Mac-1-deficient macrophages. As determined by biolayer interferometry, PF4 directly bound the αI-domain, the major ligand-binding region of Mac-1, and this interaction was governed by a of 1.3 ± 0.2 μm Using the PF4-derived peptide library, synthetic peptides duplicating the αI-domain recognition sequences and recombinant mutant PF4 fragments, the binding sites for αI-domain were identified in the PF4 segments Cys-Ser and Ala-Ser These results identify PF4 as a ligand for the integrin Mac-1 and suggest that many immune-modulating effects previously ascribed to PF4 are mediated through its interaction with Mac-1.

A single-cell transcriptional roadmap of the mouse and human lymph node lymphatic vasculature

“…fLECs and Marco-LECs, both macrophage-rich niches [16], share high expression of Csf1 (Figure 7), and fLECs express Platelet factor 4 ( Pf4 ) (also known as CXCL4) (Figures 4B and S4). CSF-1 and CXCL4 both regulate monocyte and macrophage functions [17; 43] and LEC-derived CSF-1 is required to maintain the LN macrophage niches [17]. As mentioned earlier, Bmp2 is specifically expressed by fLECs (Figures 4B, S4 and S5) that are also enriched for both Smad1 and Smad4 (Figures 4B and S4) suggesting a role for BMP-signaling in fLEC homeostasis.…”

β2 Integrins—Multi-Functional Leukocyte Receptors in Health and Disease

“…Therefore, β2 integrins enable a cell to adhere to the endothelium, and to extravasate blood vessels at inflamed sites [84]. As mentioned above, of all β2 integrins T cells express only LFA-1 [62], whereas myeloid cells (PMN, monocytes/macrophages and conventional DC) coexpress both LFA-1 and MAC-1 [63,64].…”

“…LFA-1 is rather ubiquitously expressed [62], whereas MAC-1 is predominantly apparent on myeloid cells, including PMN, monocytes/macrophages, and conventional dendritic cells (DC) [63]. In addition, it has been reported that MAC-1 is also present on the surface of NK (natural killer) cells and fractions of mast cells, B cells, CD8 + T cells, and CD4 + γδ T cells [64]. In mouse, CD11c/CD18 is rather specifically expressed by all DC populations, and accordingly serves as a well-accepted pan-DC marker [65].…”

Genome-Wide Association Studies for Immunoglobulins in Colostrum and Serum in Chinese Holstein

“…ITGAM gene encodes the integrin alpha M chain. The alpha M beta 2 integrin is important in the adherence of neutrophils and monocytes to stimulated endothelium, and also in the phagocytosis of complement coated particles and ITGAM as a ligand for the integrin Mac-1 and suggest that many immune-modulating effects previously ascribed to PF4 are mediated through its interaction with Mac-1 [53]. TGFB1I1 encodes a coactivator of the androgen receptor, a transcription factor which is activated by androgen and has a key role in male sexual differentiation.…”