To examine whether cell-cell interaction mediated the lung protection induced by d7EB cell transplantation, studies were performed in mice depleted of macrophage and monocyte populations using GdCl 3 in combination with anti-Gr1 and anti-NK1.1 antibodies injected i.v. 24 hours before CLP challenge. Mortality was higher in these mice after CLP, which could not be prevented by d7EB cell transplantation ( Figure 4C) . Thus, d7EB cell interaction with macrophage or monocytic cells is important in the mechanism of protection.