Opsonization

Both globulins exert their effect by depletion of circulating lymphocytes either by complement-dependent lysis or by phagocytosis after opsonization. However, antilymphocyte globulin (ALG) and antithymocyte globulin (ATG) are nonhuman polyclonal antibodies. To prevent sensitization application is restricted to a time period of several days only. 

IgM opsonizes indirectly by activating complement. This produces C3b, which is an opsonin. 

IgG Main antibody in the secondary response. Opsonizes bacteria, making them easier to phagocytose. Fixes complement, which enhances bacterial killing. Neutralizes bacterial toxins and viruses. Crosses the placenta. 

Microorganisms are more readily phagocytosed when coated with antibody (opsonized). This is due to the presence on the white blood cells of receptors for the Fc fragment ofIgM and IgG (discussed in Chapter 14). Avoidance of opsonization will clearly enhance the chances of survival of a particular pathogen. A substance called... 

It has the ability to cross the placenta and therefore provides a major line of defence against infection for the newborn. This can be reinforced by transfer ofcolostral IgG across the gut mucosa of the neonate. It diffuses readily into the extravascular spaces where it can act in the neutralization of bacterial toxins and can bind to microorganisms enhancing the process of phagocytosis (opsonization). This is due to the presence on the phagocytic cell surface of a receptor for Fc. 

SOZ Serum-opsonized zymosan SP Sulphapyridine SR Systemic reaction sr Sarcoplasmic reticulum SRBC Sheep red blood cells SRS Slow-reacting substance SRS-A Slow-reacting substance of anaphylaxis STZ Streptozotocin Sub P Substance P... 

Opsonization The process by which an antigen is altered so as to become more readily and more efficiently engulfed by phagocytes. 

Wang TT, Fellows PF, Leighton TJ et al (2004) Induction of opsonic antibodies to the gamma-D-glutamic acid capsule of Bacillus anthracis by immunization with a synthetic peptide-carrier protein conjugate. FEMS Immunol Med Microbiol 40 231-237... 

Runyon BA Patients with deficient ascitic fluid opsonic activity are predisposed to spontaneous bacterial peritonitis. Hepatology... 

Figure 8.9 Increased expression of IgG Fc receptors on phagocytes results in enhanced phagocytosis. These receptors will retain opsonized (i.e. antibody-coated) infectious agents at their surface by binding the Fc portion of the antibody. This facilitates subsequent phagocytosis...

Additional contributing factors include functional asplenia (and increased risk of bacterial infection), deficient opsonization, and coagulation abnormalities. 

A common characteristic of most CNS bacterial pathogens (e.g., H. influenzae, Escherichia coli, and N. meningitidis) is the presence of an extensive polysaccharide capsule that is resistant to neutrophil phagocytosis and complement opsonization. 

Humoral immunity is characterized by the production of antigen-specific antibodies that enhance phagocytosis and destruction of microorganisms through opsonization. Thus, deficiencies of humoral immunity (B lymphocytes) may lead to reduced antibody titers and are typically associated with acute gram-positive... 

Mevorach, D., 2000, Opsonization of apoptotic cells implications for uptake and autoimmunity, A , NY Acad. Sci. 926 226-235. 

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