Serum from most normal persons contains specific antibodies which react with common bacterial species preparing their surfaces so that phagocytosis by leukocytes can take place. The Fab part of these antibodies reacts with immunologic specificity with antigens on the surface of bacteria. Another part of the immunoglobulin molecule termed the Fc portion is activated during the attachment of the Fab portion to bacteria and becomes a site for attachment of bacteria to receptors on the surface of phagocytic cells. This activity is greatly amplified by heat-labile serum factors.

Normally bacteria are rapidly killed by human polymorphonuclear leukocytes after engulfment occurs. However staphylococci and gram-negative species of bacteria survive in the leukocytes of patients with the syndrome "Chronic Granulomatous Disease of Childhood."

These patients have suffered recurrent severe infections with bacterial species that are part of the body's resident bacterial flora. By contrast these patients are not at increased risk to infection from such pyogenic bacterial species as group A streptococci or pneumococci. The leukocytes from patients with chronic granulomatous disease produce little hydrogen peroxide during phagocytosis. Catalase-producing staphylococci and gram-negative bacteria are not killed, but hydrogen peroxide-producing streptococci and pneumococci are killed. A normal metabolic response to phagocytosis as well as release of lysosonial factors are essential for the bactericidal activity of human polymorphonuclear leukocytes.

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