Now these antigens can either float around our blood, our lymph or our tissue. Or the antigens can be picked up by some other type of white blood cell. For example a dendritic cell or a macrophage. Now let's suppose our antigen is picked up by the macrophage. What the macrophage will do is it will display that antigen bound to a special type of protein complex on the membrane of the macrophage. And the protein complex is known as the major histocompatibility class two complex.