14th February 2024

Summary

This refers to a deficiency in any part of the complement cascade (C1 – C9). These are usually hereditary, but some are not clinically significant and do not lead to recurrent infections. There is, however, a strong association between complement deficiency, SLE and hereditary angioedema. Patients with deficiencies in the early components of the classical complement pathway, such as C1, C2 and C4, will get recurrence of infection with encapsulated bacteria, such as Strep. Pneumoniae and Haemophilus Influenza. A deficiency in components of the final common pathway, C5 – C9, causes an increased susceptibility to infections from Neisseria spp.

Image Source: Wikimedia Commons (2019). Complement pathway, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/0/0b/Complement_pathway.png  (Accessed: 9 January 2024).