White blood cells 1: non-malignant disorders.

Disorders of white cells are very common in clinical practice. White-cell development and numbers are controlled by a mixture of external stimuli including cytokines, matrix proteins, and accessory cells. Several different white-cell lineages are recognised; each has a role in host defence. Both white-cell deficiency and overproduction can lead to disease. Some forms of inherited white-cell deficiency are potentially treatable with gene therapy.