Low levels of the innate immune system proteins MASP‐2 and MAp44 in patients with common variable immunodeficiency

Patients with common variable immunodeficiency (CVID) display low antibody levels and associated symptoms, including an increased risk of infections. The causes of CVID are uncertain and likely heterogeneous. The complement system protects against pathogens and plays essential roles in homeostasis and development. The influence of the complement system in CVID is not established. We investigated CVID patients and healthy individuals for plasma levels of the complement proteins: MASP‐1, MASP‐2, MASP‐3, MAp19 and MAp44. We also tested other patients with symptoms similar to the CVID patients. CVID patients had lower average MASP‐2 and MAp44 levels than healthy individuals (P < 0.01); the MASP‐2 level was 0.73‐fold lower, and the MAp44 level was 0.87‐fold lower. This was not observed in the other patient cohorts studied. Our findings in this exploratory study provide new insights into CVID and introduce a complement perspective for future investigations into the underlying mechanisms of the disease.