deficit of white blood cells
A low white blood cell count can be caused by a range of different conditions, from diseases to bone marrow failure, according to the National Institutes of Health. It can also be caused by a vitamin deficiency, though not generally as a result of a B-12 deficiency.
White Blood Cells. There are four main components of blood: red blood cells, white blood cells, platelets and plasma. White blood cells protect your body from infections and foreign bodies. A low white blood cells count means your body has a harder time fighting viruses, bacteria and other foreign bodies.