White blood cell. Coloured scanning electron micrograph (SEM) of a normal T-lymphocyte or T- cell, a type of white blood cell. Characteristic of normal T-lymphocytes are the long microvilli projecting from the cell surface. T-lymphocytes are susceptible to infection by the Human Immunodeficiency Virus (HIV), the causative agent of Acquired Immune Deficiency Syndrome (AIDS). There are three major types of white blood cells: granulocytes, lymphocytes and monocytes. Together they are part of the immune system which protects the body against invasion by foreign organisms and they participate in producing antibodies. Magnification: x3,500 at 6x7cm size. x12,000 at 8x10"~LANDSCAPE"