White blood cells in a blood smear, illustration - stock illustration

Lymphocyte (right down), monocyte (left) and neutrophil (right up) white blood cells in a blood smear, computer illustration. Lymphocytes are involved in the production of antibodies and attacking virus-infected and tumour cells. White blood cells are part of the body's immune system. Monocytes are the largest white blood cell. They engulf and digest invading bacteria and cell debris. Neutrophils are the most abundant white blood cell. They engulf and digest invading bacteria. Lymphocytes are involved in the production of antibodies and attacking virus-infected and tumour cells.