Leukocytes as secretory organs of inflammation.

Polymorphonuclear leukocytes secrete substances that defend against foreign invaders by mechanisms that bear remarkable resemblances to those of exocrine and endocrine glands. Similarly, leukocyte secretions can also damage the very host they are intended to protect. Like other secretory cells, leukocytes also bear surface receptors to detect signals that initiate secretion. Clinical implications are detailed.