PMID: 2091785Jan 1, 1990Paper

Complement components and receptors: deficiencies and disease associations

Immunology Series
W R Bartholomew, T C Shanahan

Abstract

The complement system, accessory to many immunological functions, consists of a number of interdependent components and receptors. Numerous in vitro approaches have elucidated the biological role of these components and receptors. However, it is the in vivo "natural" experiments that underscore their importance. The phagocytosis and subsequent digestion of pyogenic bacteria is significantly enhanced by the fixation of the third complement component to the bacterial cell wall. Equally important is the intact expression of a receptor (CR3) for the C3b cleavage fragment. Breakdown in this ligand-receptor interaction due to either C3 or CR3 deficiency leads to pyogenic infection. Interestingly, C3-deficient individuals do not demonstrate leukocytic infiltration at the site of infection. Undoubtedly, this is due to the lack of C5 convertase and failure to produce C5a. CR3-deficient individuals, on the other hand, do demonstrate leukocytosis since the third complement component is functional. C3 deficiency is not necessarily a primary lesion and may be secondary to factor I deficiency. In this case, the C3b fragment, along with factor B, acts as a C3 convertase. Inefficient inactivation of C3b, due to factor I deficiency, leads to th...Continue Reading

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