Ficolin-2 inhibitors are present in sera after prolonged storage at -80 °C

Pitfalls in complement analysis: A systematic literature review of assessing complement activation

Background

The complement system is an essential component of our innate defense and plays a vital role in the pathogenesis of many diseases. Assessment of complement activation is critical in monitoring both disease progression and response to therapy. Complement analysis requires accurate and standardized sampling and assay procedures, which has proven to be challenging.

Objective

We performed a systematic analysis of the current methods used to assess complement components and reviewed whether the identified studies performed their complement measurements according to the recommended practice regarding pre-analytical sample handling and assay technique. Results are supplemented with own data regarding the assessment of key complement biomarkers to illustrate the importance of accurate sampling and measuring of complement components.

Methods

A literature search using the Pubmed/MEDLINE database was performed focusing on studies measuring the key complement components C3, C5 and/or their split products and/or the soluble variant of the terminal C5b-9 complement complex (sTCC) in human blood samples that were published between February 2017 and February 2022. The identified studies were reviewed whether they had used the correct sample type and techniques for their analyses.

Results

A total of 92 out of 376 studies were selected for full-text analysis. Forty-five studies (49%) were identified as using the correct sample type and techniques for their complement analyses, while 25 studies (27%) did not use the correct sample type or technique. For 22 studies (24%), it was not specified which sample type was used.

Conclusion

A substantial part of the reviewed studies did not use the appropriate sample type for assessing complement activation or did not mention which sample type was used. This deviation from the standardized procedure can lead to misinterpretation of complement biomarker levels and hampers proper comparison of complement measurements between studies. Therefore, this study underlines the necessity of general guidelines for accurate and standardized complement analysis

Associations of ficolins and mannose-binding lectin with acute myeloid leukaemia in adults

We investigated clinical associations of ficolins and mannose-binding lectin (MBL) in 157 patients suffering from acute myeloid leukaemia (AML). Concentrations of ficolin-1, ficolin-2, ficolin-3 and MBL (before chemotherapy) in serum were determined as were selected polymorphisms of the corresponding genes (FCN1, FCN2, FCN3 and MBL2). The control group (C) consisted of 267 healthy unrelated individuals. Median level of ficolin-1 in patients was lower (p < 0.000001) while median levels of ficolin-2, ficolin-3 and MBL were higher (p < 0.000001, p < 0.000001 and p = 0.0016, respectively) compared with controls. These findings were generally associated with AML itself, however the highest MBL levels predicted higher risk of severe hospital infections (accompanied with bacteremia and/or fungaemia) (p = 0.012) while the lowest ficolin-1 concentrations tended to be associated with prolonged (> 7 days) fever (p = 0.026). Genotyping indicated an association of G/G homozygosity (corresponding to FCN1 gene - 542 G > A polymorphism) with malignancy [p = 0.004, OR = 2.95, 95% CI (1.41-6.16)]. Based on ROC analysis, ficolin-1, -2 and -3 may be considered candidate supplementary biomarkers of AML. Their high potential to differentiate between patients from non-malignant controls but also from persons suffering from other haematological cancers (multiple myeloma and lymphoma) was demonstrated.

Classical and lectin complement pathways and markers of inflammation for investigation of susceptibility to infections among healthy older adults

Background

There is increasing recognition of the significance of chronic, low-level inflammation in older adults, or "inflammaging." Innate immune responses and host-bacterial interactions are recognized as key factors in inflammaging. Inflammatory cytokine IL-6, and complement protein C1q have been identified as biomarkers for the development of frailty and aging-related diseases. Older adults are also susceptible to infections with serotypes of Streptococcus pneumoniae that bind ficolin-2, a component of the lectin complement pathway, and low ficolin-2 levels could possibly be involved in such susceptibility.

Methods

The aim of our study was to evaluate complement pathway components and biomarkers for inflammaging among older adults in order to investigate potential innate immune mechanisms that may account for susceptibility to infections in this population. We compared inflammatory markers, as well as components/activity of the classical and lectin complement pathways between healthy older and younger adults. We hypothesized that older adults would have higher levels of inflammatory markers and C1q, and lower levels of lectin pathway components. Older (≥70 years old) and younger (19-54 years old) adults without significant smoking history or chronic medical conditions were eligible for participation. Inflammatory markers (IL-6, TNF-α, CRP), classical complement pathway activity (CH50) and protein levels (C1q, C3, C4), and lectin pathway (MBL levels/activity, CL-L1, MASP-1/2/3, MAp44, MAp19, and H/M/L-ficolin) were compared between groups.

Results

Older adults had significantly higher mean levels of IL-6 and TNF-α. There were no significant differences in lectin pathway components between older and younger adults. Unexpectedly, mean C1q was significantly higher in the younger group in both unadjusted and adjusted analyses. There was also a significant association between race and C1q levels, but this association did not completely account for the observed differences between age groups.

Conclusions

We did not observe deficiencies in lectin pathway components to account for increased susceptibility to ficolin-binding serotypes of S. pneumoniae. Elevated levels of inflammatory cytokines in older adults are suggestive of inflammaging. However, the observed age and race-associated changes in C1q have not been previously reported in the populations included in our study. These findings are relevant to the investigation of C1q in aging-related pathology, and for its proposed role as a biomarker for frailty and disease.

Associations of Ficolins With Hematological Malignancies in Patients Receiving High-Dose Chemotherapy and Autologous Hematopoietic Stem Cell Transplantations

A prospective study of 312 patients [194 with multiple myeloma (MM) and 118 with lymphomas (LYMPH)] receiving high-dose chemotherapy and autologous hematopoietic stem cell transplantation (auto-HSCT) was conducted. Ficolins are innate immune defense factors, able to distinguish between "self" "abnormal self," and "non-self" and contribute to the elimination of the last two by direct opsonization and/or initiation of complement activation via the lectin pathway. Concentrations of ficolin-1, ficolin-2, and ficolin-3 in serially taken serum samples were determined as were the polymorphisms of the corresponding (FCN1, FCN2, and FCN3) genes. Serum samples were collected before conditioning chemotherapy, before HSCT, and once weekly post-HSCT (four to five samples in total); some patients were also sampled at 1 and/or 3 months post-transplantation. The control group (C) consisted of 267 healthy unrelated individuals. Median ficolin-1 and ficolin-2 (but not ficolin-3) levels in MM patients' sera taken before chemotherapy were lower (and correspondingly frequencies of the lowest concentrations were higher) compared with controls. That appeared to be associated with the malignant disease itself rather than with post-HSCT complications (febrile neutropenia, infections accompanied, or not with bacteremia). Higher frequencies of the FCN1 genotype G/A-C/C-G/G (corresponding to polymorphisms at positions -542, -144, and +6658, respectively) and FCN2 gene heterozygosity for the -857 C>A polymorphism were found among patients diagnosed with MM compared with the C group. Furthermore, FCN2 G/G homozygosity (-557 A>G) was found more frequently and heterozygosity G/T at +6424 less frequently among LYMPH patients than among the healthy subjects. Heterozygosity for +1637delC mutation of the FCN3 gene was more common among patients diagnosed with lymphomas who experienced hospital infections. Although no evidence for an association of low ficolin-1 or ficolin-2 with infections during neutropenia following chemotherapy before HSCT was found, we observed a possible protective effect of ficolins during follow-up.

Ficolin-2 binds to serotype 35B pneumococcus as it does to serotypes 11A and 31, and these serotypes cause more infections in older adults than in children

Among 98 serotypes of Streptococcus pneumoniae, only a small subset regularly causes invasive pneumococcal diseases (IPD). We previously demonstrated that serotype 11A binds to ficolin-2 and has low invasiveness in children. Epidemiologic data suggested, however, that serotype 11A IPD afflicts older adults, possibly indicating reduced ficolin-2-mediated immune protection. Therefore, we studied the epidemiology of ficolin-2-bound serotypes. We obtained IPD case data from the United States Centers for Disease Control and Prevention. We studied three prominent ficolin-2-bound serotypes and their acetyltransferase-deficient variants for ficolin-2 binding and ficolin-2-mediated complement deposition with flow-cytometry. We determined the age distributions of these serotypes from the obtained epidemiologic data. We discovered that the serotype 35B capsule is a novel ficolin-2 ligand due to O-acetylation via WciG. Ficolin-2-mediated complement deposition was observed on serotypes 11A and 35B but not serotype 31 or any O-acetyl transferase deficient derivatives of these serotypes. Serotypes 11A, 35B, and 31 cause more IPD among older adults than children. Studies of the three serotypes provide additional evidence for ficolin-2 providing innate immunity against IPD. The skewed age distribution of the three serotypes suggests that older adults have reduced ficolin-2-mediated immunity and are more susceptible to these serotypes.

Ficolin-2 triggers antitumor effect by activating macrophages and CD8+ T cells

Ficolin-2 is an important serum complement lectin. Here, we describe novel findings indicating that serum ficolin-2 concentrations in multiple tumor patients are significantly lower than those in healthy donors. Administration of exogenous ficolin-2 or ficolin-A (a ficolin-2-like molecule in mouse), with only once, could remarkably inhibit the tumor cells growth in murine tumor models via early macrophages, dendritic cells (DCs) and CD8+ T cells, but not CD4+ T cells. Ficolin-A (FCN-A) knockout (KO) mice exhibits significantly increased tumor cell growth. Ficolin-2 induces macrophage activation, promotes M1 polarization and facilitates proliferation and antigen-specific cytotoxicity of CD8+ T cells. Ficolin-2 binds to Toll-like receptor 4 (TLR4) on macrophages and DCs and promotes their antigen-presenting abilities to CD8+ T cells. Our findings provide a new therapeutic strategy for tumors based on the triggering of immune-mediated antitumor effect by ficolin-2.