There are five categories of white blood cells, and the two most important components are neutrophils and lymphocytes. The total white blood cell count will only be low if both of these cells become low at the same time. This can be seen in hyperfunction of the spleen, which destroys more blood cells, there will be a lower total white blood cell count and a lower neutrophil and lymphocyte count. Aplastic anemia, a disease of the blood system, can also lead to a decrease in the number of neutrophils and lymphocytes, or a decrease in the differentiation capacity of the primitive cells that produce neutrophils and lymphocytes, so that the total white blood cell count is also reduced. Some particularly serious infections can lead to a decrease in white blood cell count, but if the infection is controlled, the white blood cell count and neutrophil and lymphocyte counts can gradually return to normal. Long-term exposure to radiation or chemical toxins can also significantly lower the white blood cell count.