Spontaneous complement deficiencies give us clues to the biological functions of complement in humans (Table 2). Deficiency of C3 produces a predisposition to bacterial infection that can be lethal. Such patients also display a deficient repertoire of antibodies, possibly due to a lack of CR2-mediated lymphocyte events in the absence of C3b-mediated opsonization of new antigens. C3 deficiency occurs in several different ways: a genetic lack of C3 production, a secondary loss due to accelerated fluid-phase cleavage from an inborn deficiency of factor 1 or factor H, or acquisition of an autoantibody that causes C3 activation. Excess bacterial infections are seen in patients with granu-locyte deficiencies of CR3 and other adhesion molecules or with deficiencies of properdin. Immune complex diseases result from deficiencies of erythrocyte CR1 expression or of classical pathway proteins, as (in primates) the classical pathway produces immune complex clearance. Patients deficient in C8 or C9 display increased susceptibility to infection by Neisseria bacterial species.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.