Model for early neutrophil and late macrophage activation. Apoptotic cells are recognised and phagocytosed by their neighbouring epithelial cells or professional and semi-professional cells (curved black arrows). This recognition and/or phagocytosis might involve LBP, CD14, signalling down by means of the Toll-like receptor 4 (TLR4). Activation of this receptor could lead to secretion of the neutrophil-attracting chemokine GRO1/IL-8 (red arrow) and to the attraction of neutrophils to the area of trauma (yellow arrow). This is followed by secretion of the CD14+-monocyte-attracting chemokine BMAC (broken arrow), which could lead to monocyte infiltration on days 3 and 4 of involution (yellow arrow); monocytes would subsequently differentiate into macrophages.