Complement Deficiency
• C3 has the highest serum concentration. C9 has the lowest serum concentration and the lowest molecular weight. The one with the highest molecular weight is Clq.
• Insufficient number or function of the complements increases the tendency to infections. Properdin deficiency is X-linked; Other complement deficiencies are autosomal recessive.
Findings in complement deficiencies
1. Recurrent infections with extracellular pyogenic microorganisms (pneumococci, gonococci, meningococci, H. influenzae), severe and recurrent respiratory tract and skin infections are common.
2. High incidence of autoimmune disease (SLE).
3. Vasculitis is common.
4. Chronic nephritis (MPGN) is common.
5. Partial lipodystrophy may be seen.
Diagnosis of complement deficiencies
• For complement abnormalities, the total hemolytic complement activity test (CH50) is a good screening tool. CH50<5% is suggestive of deficiency.
• In Cl-C8 deficiencies, the CH50 level is 0 or close to 0. In C9 deficiency, CH50 is half of normal.
• Co-reduction of C4 and C3 indicates that the classical pathway is activated by immune-complexes.
• If C3 is low, C4 is normal, it indicates that the alternative pathway is activated.
• MPGN contains nephritic factor (NF). This NF activates the alternative complement pathway, resulting in decreased C3. Patients also have partial lipodystrophy.
CH50: The classic way
AP50: Indicates alternative pathway disturbance
• C19 failure: SLE or SLE-like syndrome, vasculitis and MPGN are common.
• C1r, C1s, C4, C2, C4 deficiencies: The incidence of autoimmune disease has increased.
• C5, 6, 7, 8, 9 deficiencies: Recurrent meningococcal meningitis is seen.
• C2 deficiency: Life-threatening pneumococcal sepsis is common.
• C3 deficiency: Severe and recurrent pneumococcal and meningococcal infections are seen.
• Plasma membrane control proteins: Factor 1/ Factor H, C4 binding protein, Properdin and C1 inhibitor.
• Membrane complement components: CR1, membrane cofactor protein and degradation accelerating factor (DAF). Paroxysmal nocturnal hemoglobinuria is seen in DAF and CD59 deficiency.
• In serosal complement control protein deficiency, the chemotactic activity of CSa and IL-8 cannot be inhibited, and this is seen in FMF.
• Factor H, I and protein B deficiency: familial (genetic) hemolytic uremic syndrome
• C2 deficiency: OR passes. SLE-like findings, Anti-DNA ( + ), MPGN and CRF are common findings.
Immune defects associated with lymphocytes
