When pathogens invade the lungs, the inflammatory process causes fluid to accumulate in the affected alveoli. In a process called hepatization, capillaries dilate and neutrophils, red blood cells (RBCs), and fibrin fill the alveoli, causing the lung to appear red and granular. Next, blood flow decreases and leukocytes (white blood cells) and fibrin infiltrate the area and consolidate (solidify). As the infection resolves, the consolidated material dissolves and is ingested and removed by macrophages.