POS0060 MEASUREMENTS OF COMPLEMENT ACTIVITY SPECIFICALLY THOUGH THE LECTIN -OR THE CLASSICAL PATHWAY IN PATIENTS WITH SLE

Background

In systemic lupus erythematosus (SLE), the complement system (CS) is activated and thought to occur primarily through the classical pathway (CP) [1]. Traditionally, when diagnosing SLE or assessing disease activity, measurement of low C3 or C4 are used as proxies for complement activation [2]. However, measurement of C3 and C4 does not differentiate which complement pathway initiated the activation (i.e., the lectin pathway (LP), the CP, or the alternative pathway) [1, 3].

C1-esterase inhibitor (C1inh) is one of the key regulators of the CS. C1inh is the exclusive inhibitor of the active CP enzymes C1r and C1s [4], and the major inhibitor of active LP enzymes MASP-1 and MASP-2 [5]. A possible way of assessing complement activation through a specific pathway, is by measuring activated enzymes complexed with C1inh in plasma, as these complexes only exist after complement enzyme activation.

Objectives

Our aim was to investigate and unravel LP and CP complement activation in SLE, by measuring the protein complexes MASP1/C1inh (LP specific activation) and C1r/C1inh (CP specific activation). Furthermore, we aimed to investigate whether there is an association between complement activity, disease activity (SLEDAI) and disease manifestations (lupus nephritis (LN)).

Methods

A cross sectional cohort of 150 patients with SLE fulfilling the 1997 ACR classification criteria for SLE were included from the out-patient clinic at the department of Rheumatology, Aarhus University Hospital (AUH), Denmark. Disease manifestations and disease activity using SLEDAI score was assessed at inclusion. Fifty healthy individuals included at the Blood Bank, AUH, were used as controls. Both C1s/C1inh and MASP1/C1inh complexes were measured in all samples using two newly developed sandwich ELISAs (C1s/C1inh: cat# HK399; MASP1/C1inh: Cat#3001, Hycult Biotech, Uden, The Netherlands). EDTA-samples from both SLE patients and controls were measured in duplicates.

Results

When comparing SLE patients to controls, we observed a difference in complement activation through the LP, where a lower mean MASP1/C1inh plasma concentration was observed (p<0.01).

C1s/C1inh concentrations were significantly increased in active SLE patients (SLEDAI >6) when compared to SLE patients with low disease activity (SLEDAI <6, p<0.01) and correlated with SLEDAI score (r=0.285, p<0.01). C1s/C1inh concentrations were increased in SLE patients with active LN compared to non-active LN, however this not statistically significant (p=0.09).

No differences in MASP1/C1inh plasma concentrations were observed between active SLE patients and patients with low disease activity (p=0.11), nor did we observe a significant correlation with disease activity (r=0.12, p=0.13). In active LN, plasma concentrations of MASP1/C1inh were significantly elevated compared to non-active LN (p=0.02).

Conclusion

Our data suggest that the CP and the LP is activated in SLE. CS is generally activated in active SLE disease, whereas activation of the LP might be more specific to particular disease manifestations like LN.

Our findings warrant further research into activation of the specific complement pathways in relation to specific disease manifestations in SLE.

References

[1]Troldborg, A., et al., J Rheumatol, 2018.

[2]Weinstein, A., et al., Curr Rheumatol Rep, 2021.

[3]Atkinson, J.P., Clin Exp Rheumatol, 1989.

[4]Sim, R.B., et al., FEBS Lett, 1979.

[5]Paréj, K., et al., Mol Immunol, 2013.

Figure 1.

Measurements of plasma concentrations of C1r in complex with C1-inhibitor (C1r/C1inh) (a1-a4) and MASP1 in complex with C1-inhibitor (MASP1/C1inh) (b1-b4) in Systemic Lupus Erythematosus (SLE) patients and controls. A1 and b1 show measurements of SLE patients versus controls. A2 and b2 show measurements in SLE patients with active disease (SLEDAI >6) versus low disease activity (SLEDAI<6). A3 and b3 show correlation analysis between measurements and SLEDAI score in SLE patients. A4 and b4 show measurements in SLE patients with active lupus nephritis (LN) versus non-active LN.

Disclosure of Interests

Mads Christian Lamm Larsen: None declared, Anne Troldborg: None declared, Erik Toonen Employee of: ET is an employee of Hycult Biotech, Lisa Hurler: None declared, Zoltán Prohászka: None declared, László Cervenak: None declared, Annette G Hansen: None declared, Steffen Thiel: None declared

Complete kinetic follow-up of symptoms and complement parameters during a hereditary angioedema attack

We studied the kinetics of C1-inhibitor (C1-INH) and other complement parameters in a self-limited edematous attack (EA) in a patient with hereditary angioedema due to C1-INH deficiency to better understand the pathomechanism of the evolution, course, and complete resolution of EAs. C1-INH concentration and functional activity (C1-INH_c+f ), C1(q,r,s), C3, C4, C3a, C4a, C5a, and SC5b-9 levels were measured in blood samples obtained during the 96-hour observation period. The highest C1-INH_c+f , C4, and C1(q,r,s) levels were measured at baseline, and their continuous decrease was observed during the entire observation period. C4 depletion started at prodromal phase, and C4 was lowest after the maximum severity peak. Compared to baseline, C4a level was four times higher 7 hours before the onset of the attack. C1-INH did not increase after resolution of the attack suggesting that factors other than C1-INH may be important in this process. C4a may be a useful biomarker for the prediction of EAs.

Human anti-60 kD heat shock protein autoantibodies are characterized by basic features of natural autoantibodies

Anti-human Hsp60 autoantibodies--known risk factor of atherosclerosis--were investigated in a mouse model and in samples of healthy subjects: polyreactivity, presence in cord blood samples of healthy newborns and life-long stability were tested. In IgM hybridoma panel from mouse spleens, polyreactivity of anti-Hsp60 autoantibodies was studied. In healthy pregnant women, umbilical vein and maternal blood samples were collected after childbirth, anti-Hsp-60 and -65 IgM and IgG levels were measured. Life-long stability of anti-Hsp-60 levels was studied on healthy patients during 5 years. ELISA was used in all studies. Polyreactivity of IgM clones of newborn mice and lifelong stability of these autoantibodies in healthy adults were established. IgM anti-Hsp60 autoantibodies in cord blood of healthy human infants were present, however, there was no correlation between maternal and cord blood IgM anti-Hsp60 concentrations. It is proposed that presence of anti-Hsp60 autoantibodies--as part of the natural autoantibody repertoire--may be an inherited trait. Level of anti-Hsp60 autoantibodies may be an independent, innate risk factor of atherosclerosis for the adulthood.

Changes in tear protein pattern after photorefractive keratectomy

PURPOSE

Changes in tear protein composition of patients who underwent photorefractive keratectomy (PRK) were analyzed.

METHODS

Tear samples were obtained from 23 eyes of 23 patients immediately before PRK and on the fourth postoperative day with glass capillaries. Tear proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Digital image analysis and evaluation of the densitometric data of the electrophoretic separations were done with BioDoc-Analyze.

RESULTS

Analysis of discriminance found a significant difference in the protein patterns (p < 0.001). This type of analysis of the electrophoretic densitographs uses all peak information simultaneously. A significant decrease (p < 0.005) in three of the main protein peaks--lactoferrin, immunoglobulin A heavy chain, and lysozyme--was also found after PRK.

CONCLUSIONS

Excimer laser ablation of the cornea has an acute effect on lacrimal gland protein secretion. Changes in tear composition may lead to feelings of dryness and to a decrease in tear film stability postoperatively.

Antibodies against different epitopes of heat-shock protein 60 in children with type 1 diabetes mellitus

The aim of this study was to investigate the amounts and epitope specificity of antibodies against heat shock protein 60 (hsp60) in the sera of type 1 diabetic and healthy children. Antibodies specific for peptide p277 of human hsp60 and of M. bovis as well as for human hsp60, M. bovis hsp65 proteins were measured by ELISA. Other autoantibodies (islet cell antibodies, glutamate decarboxylase antibodies and IA-2 antibodies) were also determined. A total number of 83 serum samples from children with type 1 diabetes mellitus and 81 samples of control children were investigated. Epitope scanning of the hsp60 for linear antibody epitopes was carried out using synthetic peptides attached to pins. The antibody levels specific for peptide p277 of human- and of M. bovis origin were significantly (human: P=0.0002, M. bovis: P=0.0044) higher in the diabetic children group than in the healthy children. We could not find significant difference in the antibody levels to whole, recombinant hsp proteins among the examined groups of children. Antibodies to two epitope regions on hsp60 (AA394-413 and AA435-454) were detected in high titres in sera of children with diabetes mellitus. The first region similar to the sequence found in glutamate decarboxylase, whereas the second one overlaps with p277 epitope to a large extent. Presence of antibodies to certain epitopes of hsp60 (AA394-413-glutamic acid decarboxylase-like epitope; AA435-454-p277-like epitope) in diabetic children may reflect their possible role in the autoimmune diabetogenic process of the early diabetes.

Differential expression of GL7 activation antigen on bone marrow B cell subpopulations and peripheral B cells

GL7 was originally described as a 35-kDa late activation antigen on mouse T and B cells. GL7 expression has also been demonstrated on thymocytes, germinal center B cells and some neuronal cell types. Flow-cytometry and immunohistochemistry were used to follow changes in the expression of GL7 during B cell development, amongst B cell subpopulations and various anatomical locations. GL7 is expressed as early as the pro-B cell stage and increases up to the pre-B-I stadium. Expression remains high on pre-B-II and on immature B cells, although slightly decreases during maturation. GL7 is almost completely downregulated when IgD appears on the cell surface. On the periphery only a few B cells are positive and these cells are almost exclusively found in the sIgD- germinal center areas of lymph nodes and spleen. The staining pattern of GL7 is very similar to that of PNA in the lymph nodes but in the bone marrow we have found both B220+PNA+GL7- and B220+PNA+GL7+ populations, showing that GL7 and the antigen recognized by PNA are different. After in vitro stimulation, the GL7(hi) B cell population has also been found to be IgD negative. Functional comparison between in vitro activated and MACS sorted GL7(hi) and GL7(lo/-) spleen B cells of immunized mice showed significantly higher specific and total antibody production as well as antigen presenting capacity in the GL7(hi) population.

Levels of antibodies against C1q and 60 kDa family of heat shock proteins in the sera of patients with various autoimmune diseases

Previously a strong positive correlation was found between antibodies to C1q (C1qAb) and antibodies against human heat shock protein (hsp60) and mycobacterial hsp65 in HIV infected patients. Here the levels of these antibodies were measured in the sera of patients with different autoimmune diseases (122 systemic lupus erythematosus (SLE), 55 systemic sclerosis, 33 undifferentiated connective tissue disease (UCTD), 27 primary Raynaud syndrome, 21 rheumatoid arthritis (RA), 14 polymyositis/dermatomyositis (PM/DM), and 192 healthy blood donors. The prevalence of IgG C1qAb was found to be high (P<0.0001 as compared to the healthy controls) only in the SLE group. The levels of the anti-hsp60 (P=0.0094) and anti-hsp65 (P=0.0108) antibodies were high only in the UCTD patients. No correlation was found between the C1qAb and anti-hsp antibodies in any group except a significant (P=0.011) positive correlation between C1qAb and hsp65 antibodies in the patients with UCTD. These findings indicate that the autoantibodies against C1q are heterogeneous: in different diseases different types of C1qAb may dominate.

Abolished angiogenicity and tumorigenicity of Burkitt lymphoma by interleukin-10

Because of its immunosuppressive properties, interleukin-10 (IL-10) is thought to play an important role in a number of human disease states, including inflammation, autoimmunity, and transplant rejection. In this study, we demonstrate that introduction of human or viral IL-10 genes into Burkitt's lymphoma cells markedly reduced their ability to grow as subcutaneous (sc) tumors in SCID mice. In vivo assays for angiogenesis revealed an inhibition of the angiogenic capacity of the IL-10-transfected lines. Recombinant human IL-10 abolished and viral IL-10 reduced vascular endothelial growth factor (VEGF)-165-induced neovascularization. Furthermore, IL-10 blocked the VEGF- and fibroblast growth factor (FGF)-2-induced proliferation of microvascular endothelial cells in vitro. The current observations suggest a direct role for IL-10 in the prevention of angiogenesis in human lymphoid malignancies.

CD40 cross-linking enhances the immunogenicity of Burkitt's-lymphoma cell lines

Epstein-Barr-virus (EBV)-positive Burkitt's-lymphoma (BL) cell lines are not recognized by EBV-specific T cells, due to their non-immunogenic phenotype and restricted expression of latent EBV genes. We tested whether triggering of CD40 can alter the phenotype of the tumor cells with regard to: (i) expression of surface markers, (ii) expression of viral antigens, (iii) presentation of endogenous antigens to MHC-class-1 restricted cytotoxic T lymphocytes (CTLs), (iv) stimulatory capacity in allogeneic mixed-lymphocyte cultures (MLCs), (v) sensitivity to natural-killer (NK)-cell-mediated lysis. Co-culture of EBV-positive BL cells with CD40-ligand-transfected L cells induced up-regulation of CD54 and CD80 but did not affect the expression of viral genes. In spite of significant up-regulation of TAP1 and TAP2, and increased expression of MHC class 1, the BL cells remained unable to present endogenously expressed viral antigens to EBV-specific CTL. However, the up-regulation of adhesion and co-stimulatory molecules was associated with increased stimulatory capacity in MLC and enhanced sensitivity to NK cells. These findings indicate that, while inducing only a modest phenotype shift, cross-linking of CD40 under physiologic conditions may selectively enhance the sensitivity of BL cells to anti-tumor immune responses.