Acquired deficiencies of the complement system
- M Kathryn Liszewski, PhD
M Kathryn Liszewski, PhD
- Assistant Professor of Medicine
- Washington University School of Medicine
- John P Atkinson, MD
John P Atkinson, MD
- Samuel B Grant Professor of Medicine
- Professor of Molecular Microbiology
- Chief, Division Rheumatology
- Washington University School of Medicine
Deficiencies in complement proteins may be inherited or acquired (secondary). Secondary causes of complement deficiency will be presented in this topic review. Inherited disorders of the complement system as well as a description of the complement pathways and the clinical evaluation of complement are presented separately. (See "Inherited disorders of the complement system" and "Complement pathways" and "Overview and clinical assessment of the complement system".)
Acquired deficiencies in complement proteins are more common than inherited complement disorders. Reductions in complement secondary to acquired disease processes are usually only partial and affect several complement components at once. As an example, approximately 50 percent of patients with systemic lupus erythematosus (SLE) will have reductions in C4 and C3, reflecting classical pathway activation.
These acquired complement deficiencies are most commonly encountered in diseases featuring autoantibodies. In many diseases, such as milder forms of SLE, augmented hepatic synthesis of components may be sufficient to maintain the levels in the normal range. The management of most disorders of the complement system featuring excessive activation focuses on the treatment of the underlying disorders.
MECHANISMS OF ACQUIRED COMPLEMENT DISORDERS
Acquired deficiencies in complement proteins may result from several mechanisms:
●Accelerated consumption by immune complexes (common)
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- MECHANISMS OF ACQUIRED COMPLEMENT DISORDERS
- INCREASED CONSUMPTION BY IMMUNE COMPLEXES
- Systemic lupus erythematosus
- Antiphospholipid syndrome
- Vasculitic syndromes
- Renal diseases
- - C3 nephritic factor
- - Dense deposit disease
- - C4 nephritic factor
- Autoimmune hemolytic anemia
- IgG4–positive multiorgan lymphoproliferative syndrome
- Viral infections
- Acquired angioedema
- REDUCED HEPATIC SYNTHESIS
- LOSS OF COMPLEMENT COMPONENTS IN THE URINE