Composition of blood in a blood capillary. This illustration represents all the elements that make up blood. First of all, the elements of blood are bathed in plasma. The plasma is shown in transparency in yellow. There are erythrocytes, or red blood cells or red blood cells, and platelets, antibodies and white blood cells, actors in the immune reaction. The red blood cells represented in red are the element of the blood in greater number. While the other elements are less numerous. First of all the platelets are the smallest elements (in blue) scattered around the vessel. Antibodies are shown in yellow in the shape of a Y. Then the other elements in purple are white blood cells. A T lymphocyte is located in the center of the vessel in purple and green. While the large purple cell in the foreground, as well as the one that passes through the vessel wall are leukocytes. The first is a monocyte, the second that passes through the wall is a neutrophil. Finally, outside the vessel is a macrophage which phagocyte pathogenic antigens (in green). Macrophages arise from the differentiation of monocytes. They infiltrate tissue to a site of infection.