Assessment of complement deficiencies
Complement deficiencies predispose to an increased susceptibility to infection, in particular caused by Neisseria meningitidis, and to a minor extent by Streptococcus pneumonia and Haemophils influenza (Table 1, ref 1). It is therefore of utmost importance to assess the presence of these deficiencies, especially when the patient has experienced recurrent infections. As numerous mutations have been described so far (WC), no molecular biological test can detect more than a few mutations and usually only one. In contrast, functional assays will assess both activity and presence of a number of complement proteins in a single assay and in fact, the pathway in which the defect lies can be detected. The earliest haemolytic assays, based on sheep or rabbit erythrocytes, respectively, were already able to distinguish classical from alternative deficiencies (WD).
However, these assays rely on a stable source of biological material and are interference-prone (WD). For this reason a quantitative method in ELISA format, such as the ones developed by Svar Life Science, should be preferred (Table WB). Using these kits, C4 and C2 deficiencies can be easily distinguished from C1 deficiencies. MBL and MASP 2 deficiencies can be detected as well (via the EDLP kit, Table WB).
Table WB. Complement deficiency and detection by complement activation ELISA (modified from WD)
|Complement component||Assay which will detect a deficiency via a low result|
|C1q, C1r, C1s||CH50, EDCP|
|C4, C2||CH50, EDCP+EDLP|
|C3, C5-C9||CH50+AP50 OR EDCP+EDAP|
CH50, classical pathway haemolytic assay; AP50, alternative pathway haemolytic assay; ED-CP, Svar Life Science classical pathway kit; ED-LP, Svar Life Science lectin pathway kit; ED-AP, Svar Life Science alternative pathway kit.
2. WC. Botto M, Kirschfink M, Macor P, Pickering MC, Würzner R, Tedesco F. Complement in human diseases: Lessons from complement deficiencies. Mol Immunol 2009;46:2774-2783.
3. WD. Mollnes TE, Jokiranta TS, Truedsson L, Nilsson B, Rodriguez de Cordoba S, Kirschfink M. Complement analysis in the 21st century. Mol Immunol 2007;44:3838-3849.