Macrophage and T cells Coloured scanning electron micrograph (SEM) showing the interaction between a macrophage (large cell) and a CD4+T cells, two components of the bodys immune system. Both are types of white blood cell. Macrophages are antigen-presenting cells (APCs). They present antigens (fragments on the surface of pathogens or foreign objects) to T lymphocytes, activating them. Each T lymphocyte recognises and binds to a specific antigen. Binding of the T cell to the antigen presented by the macrophage activates the T cell. This leads to its proliferation and the activation of other immune cells that eliminate the antigen. Specimen courtesy of Greg Towers and Lydia Newton, UCL. Magnification: x7000 when printed 10cm wide.