Lymph node. Light micrograph of a section through a lymph node, part of the immune system. The node contains T- and B-lymphocytes, white blood cells which can travel to sites of infection within the body. Lymph fluid flows through the nodes, and has micro-organisms filtered from it by phagocyte white blood cells. The rounded structures seen in the node are lymphoid follicles. The paler centres of the follicles are germinal centres, sites of B- lymphocyte proliferation. B-lymphocytes produce antibodies to fight infections. Magnification: x4 at 35m size.