The Alternative Complement Pathway Is Activated Without a Corresponding Terminal Pathway Activation in Patients With Heart Failure.

Objective: Dysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF. Methods: We analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls. Results: Compared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years. Conclusion: Our findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway.

A systematic analysis of the complement pathways in patients with neuromyelitis optica indicates alteration but no activation during remission.

Neuromyelitis optica (NMO) is an autoimmune demyelinating inflammatory disorder, mediated by pathogenic autoantibodies against aquaporin 4 (AQP4), the main water channel of the central nervous system (CNS). NMO is characterized by local IgG deposition and complement activation within the CNS, but the three complement pathways have not been systematically investigated. We evaluated the overall activation of the classical, alternative, and MBL-lectin pathways in the peripheral blood of 25 patients with AQP4-seropositive NMO spectrum during remission and 113 healthy controls by three ways: (1) we measured the concentrations of native complement proteins of the three pathways [C1-inhibitor (C1-inh), C1q, C4, C3, C5, factor I, factor B, properdin]; (2) the concentrations of complement products suggesting in vivo activation (C1rC1sC1-inh, C3a, C3bBbP, and SC5b-9); and (3) the total activity of the three complement pathways. Additionally we measured levels of C1rC1sC1-inh, C3a, C3bBbP in cerebrospinal fluid (CSF) of 6 patients with relapsing NMO and of 18 patients with relapsing multiple sclerosis (MS). The serological studies indicated that total complement activity of the classical [median (interquartile range) 72 (61-82) vs. 65 (56-73) CH50/mL; p=0.0122] and of the lectin pathways [73 (59-111) vs. 49 (3-92)%; p=0.0078)] were elevated compared with the controls, whereas that of the alternative pathway was not significantly different. The levels of C3 [1.1 (0.9-1.3) vs. 1.4 (1.2-1.5)g/L; p<0.0001], factor B [89 (77-115) vs. 103 (93-113)%; p=0.0397] and factor I [85 (69-95) vs. 101 (93-107)%; p=0.0007], as well as of properdin [92 (74-104) vs. 108 (97-122)%; p=0.0028] were significantly lower in the patients than in the controls. The only increase in the patients was ascertained in the relative concentration of C1rC1sC1-inh vs. the C1-inhibitor (42.3 [31.9-65.0] vs. 30.8 [13.5-43.5] AU/mg; p=0.0007). The absolute and relative levels of the other complement activation products were not elevated in the patients. On the contrary, the serum concentrations of C3a, C3bBbP, and SC5b-9 of the patients were lower than those of the controls. The absolute concentration of the complement activation products (C1rC1sC1-inh, C3bBbP, C3a) and the ratio of C3bBbP/C1rC1sC1-inh did not differ in NMO and MS CSF samples. The ratio of C3bBbP/C1rC1sC1-inh was similar in NMO plasma and CSF samples. We found a higher ratio of C3bBbP/C1rC1sC1-inh in the plasma of control subjects compared to those in any pathological samples. Our results do not indicate substantial systemic complement activation if NMO activity is adequately controlled; nevertheless, the complement system is abnormally affected even during remission. The relative ancillarity of the alternative compared to the classical pathway may also suggest that suppression of the alternative pathway by treatment may be important to achieve remission.