1 Department of Medicine, Children's Hospital Medical Center, and Department of Pediatrics, Harvard Medical School, Boston
The list of syndromes associated with diminished resistance to infection has grown bewilderingly long and complex in recent years. The busy pediatrician finds little consolation in the fact that knowledge gained from study of these specific defects has led to a more comprehensive understanding of normal immune mechanisms. Yet, this new insight has permitted a logical grouping of syndromes which can provide the physician with order and confidence in his diagnostic endeavors. One possible classification of immune deficiencies is offered here, primarily as a basis for some suggestions as to what should make a pediatrician suspect an immune defect and how he can test his suspicions. The reader is encouraged to substantiate the framework presented here with more detailed reviews.1-5
Mechanisms of resistance to infection may be separated into four major systems: physico-anatomical barriers, phagocytosis, humoral factors, and cellular immunity.
PHYSICO-ANATOMICAL BARRIERS
Defects of this "system" are often confined to one anatomical area or, at least, predispose to infections of a localized site. Cystic fibrosis, urethral stenosis, foreign bodies, eczema, skull fracture, and, occasionally, asthma are examples. Sickle cell disease, indwelling intravenous catheters, and prolonged broad-spectrum antibiotic therapy may induce generalized or localized infection. Diagnostic techniques applicable to this group are well known to pediatricians.
PHAGOCYTOSIS
The body clears bacterial invaders largely through the process of phagocytosis. Resistance to infection by fungi and viruses, on the other hand, depends primarily upon the integrity of the small lymphocyte, through a mechanism which is not yet understood. Thus, a patient with an abnormality of phagocytosis has little difficulty with fungal or viral infections if his lymphocytes are normal, but he is threatened by bacteria, especially those not easily killed by other defense mechanisms.