FN-C1q and C1 INH C1r-C1s complexes as indicators of complement activation in patients with chronic lymphocytic leukaemia

A C5a-Immunoglobulin complex in chronic lymphocytic leukemia patients is associated with decreased complement activity

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the Western world. The therapeutic approach to CLL includes chemotherapeutic regimens and immunotherapy. Complement-mediated cytotoxicity, which is one of the mechanisms activated by the therapeutic monoclonal antibodies, depends on the availability and activity of the complement (C) system. The aim was to study the structure of circulating C components and evaluate the importance of C5 structural integrity for C activity in CLL patients. Blood samples were collected from 40 naïve CLL patients and 15 normal controls (NC). The Western blot analysis showed abnormal C5 pattern in some CLL patients, while patterns of C3 and C4 were similar in all subjects. Levels of the C activation markers sC5b-9 and C5a were quantified before and after activation via the classical (CP) and alternative (AP) pathways. In patients with abnormal C5, basal levels of sC5b-9 and C5a were increased while activities of the CP and of the CP C5-convertase, the immediate C5-upstream complex, were decreased compared to NC and to patients with normal C5. The data indicate a link between CP activation and apparent C5 alterations in CLL. This provides a potential prognostic tool that may personalize therapy by identifying a sub-group of CLL patients who display an abnormal C5 pattern, high basal levels of sC5b-9 and C5a, and impaired CP activity, and are likely to be less responsive to immunotherapy due to compromised CP activity.

Notch2 controls non-autonomous Wnt-signalling in chronic lymphocytic leukaemia

The Wnt signalling pathway, one of the core de-regulated pathways in chronic lymphocytic leukaemia (CLL), is activated in only a subset of patients through somatic mutations. Here we describe alternative, microenvironment-dependent mechanisms of Wnt activation in malignant B cells. We show that tumour cells specifically induce Notch2 activity in mesenchymal stromal cells (MSCs) required for the transcription of the complement factor C1q. MSC-derived C1q in turn inhibits Gsk3-β mediated degradation of β-catenin in CLL cells. Additionally, stromal Notch2 activity regulates N-cadherin expression in CLL cells, which interacts with and further stabilises β-catenin. Together, these stroma Notch2-dependent mechanisms induce strong activation of canonical Wnt signalling in CLL cells. Pharmacological inhibition of the Wnt pathway impairs microenvironment-mediated survival of tumour cells. Similarly, inhibition of Notch signalling diminishes survival of stroma-protected CLL cells in vitro and disease engraftment in vivo. Notch2 activation in the microenvironment is a pre-requisite for the activation of canonical Wnt signalling in tumour cells.

Discovery and Identification of Potential Biomarkers in a Prospective Study of Chronic Lymphoid Malignancies Using SELDI-TOF−MS

The accurate diagnosis of the different forms of chronic mature B-cell lymphocytic malignancies is of primary importance to determine an appropriate and efficient treatment. Usually, the diagnosis is achieved by morphology and immunophenotyping. Nevertheless, the diagnostic tools available are not able to discriminate pathologies with variable evolution, or to classify some of them. To discover new biomarkers, we used peptide and protein profiling SELDI-TOF-MS, to analyze 39 chronic B-cell malignancies and 20 control serum samples. Markers of interest were subsequently identified and characterized. In the obtained SELDI-MS profiles, most of the differences were observed in three mass ranges (m/z = 13 000; m/z = 9000; m/z < 2000). Identification of these biomarkers was achieved either by direct enrichment on the ProteinChip arrays followed by on-chip-MS/MS or by chromatographic fractionation, 1D-gel followed by nanoLC-MS/MS analysis. An increase of a sulfite form of transthyretin (13,841 Da) was observed in the patient group. A second set of markers at 8.6 and 8.9 kDa was identified as complement related fragment proteins, the C3a and C4a anaphylatoxins. In the low mass range, several peptides originating from N-terminal and C-terminal processing of the C3 alpha and C4 alpha chains were specifically observed in 38% of the patient sera, but in none of the control sera. This study emphasizes the usefulness of mass spectrometry studies in such malignancies.

Two parallel routes of the complement-mediated antibody-dependent enhancement of HIV-1 infection

OBJECTIVE

To study the mechanism of the complement-mediated antibody-dependent enhancement (C'-ADE) of HIV infection which may play a significant role in the progression of HIV-disease.

METHODS

In vitro complement activating and complement-mediated HIV-infection enhancing abilities of three human anti-gp41 monoclonal antibodies (MAb) were tested. C'-ADE was estimated using HIV-1IIIB and CR2 (CD21)-carrying MT-4 target cells. Normal human serum (NHS), purified C1q, C1q-deficient (C1qD) and C2-deficient (C2D) human sera were applied as complement sources.

RESULTS

All MAb mediated increased C1q binding to solid-phase gp41. All MAb had a marked dose-dependent and strictly complement-mediated HIV-infection enhancing effect. Mixtures of the MAb with purified C1q also significantly increased HIV-1 infection. C1qD serum had a markedly lower enhancing effect than NHS, which could be raised to normal level by addition of purified C1q. Pretreatment of the target cells with anti-CR2 antibodies only partially inhibited the enhancing effect of the MAb plus normal human serum.

CONCLUSION

These novel findings indicate that besides the well-known facilitation of entry of HIV-1 by the interaction between virus-bound C3 fragments and CR2 present on the target cells, fixation of C1q to intact virions also results in an enhanced productive HIV-1 infection in the MT-4 cell cultures.

Low activity of the classical complement pathway predicts short survival of patients with chronic lymphocytic leukaemia

The activities of the classical (CP) and alternative (AP) complement pathways as well as the levels of some complement components and circulating immune complexes were measured in 43 patients with chronic lymphocytic leukaemia (CLL) between 1980 and 1984. Depressed CP activities were frequently found in these patients. Clinical course of the disease in the patients was followed until 1992, and compared with the initial complement values. During the follow-up period 36 patients died, death of 33 patients being related to the underlying disease. A strong positive correlation (P < 0.01) was found between the length of survival of the patients and the initial CP values. Patients were divided into two groups: group A, short-term survivors, i.e patients who died in CLL-related complications within 3 years after the complement measurements; and group B, long-term survivors who died > or = 4 years after the complement measurements due to any cause, or were alive at the end of the follow-up period. Average CP values in Group B were almost twice those in group A (P = 0.002), and a similar but less pronounced difference was found in C3 levels (P = 0.055). These differences were even more marked (P = 0.0006 and P = 0.0015, respectively) when only patients in Rai stage 2 and 3 were considered. Low classical pathway activities predicted short survival time: according to the logrank test, patients in Rai stage 2-3 with low (< mean - 2s.d. of the normal values), and normal CP levels survived for 2.0 +/- 1.1, and 4.6 +/- 3.0 years, respectively. All the nine and 11/13 patients with low CP and C4 levels, respectively, died within 3 years after the complement measurements were made. These findings indicate that complement measurements performed in CLL patients have a clinical value.

Studies on the mechanism of complement-mediated inhibition of antibody binding to HIV gp41

We have previously demonstrated that HIV envelope gp41 binding to specific antibodies decreases after preincubation of fluid-phase gp41 in normal human serum. This inhibition is proven to be mediated by the classical complement pathway. In this study recombinant gp41 (rgp41) and/or synthetic peptides were preadsorbed to solid phase, and then complement (normal human serum/heated human serum/purified Clq/heated Clq) and anti-gp41 antibodies were added either after each other or simultaneously, and the amounts of bound antibody, and deposited C3b, C4b and Clq were measured. Complement-dependent inhibition of antibody binding to solid-phase rgp41 was found, and Clq seems to be at least partially responsible for this phenomenon. Heating of Clq did not affect this process. Higher amounts of anti-gp41 antibodies significantly and dose-dependently enhanced C4b and C3b fixation to solid-phase rgp41. In the case of synthetic peptides corresponding to the immunodominant region of gp41, significant antibody binding to the solid-phase peptides was also detected, and pretreatment of peptides preadsorbed to solid phase with normal human serum almost totally abolished the antibody binding.

Complement research: biosynthesis, genetics, immunoregulatory role and clinical studies

Complementology is one of the major areas of immunological research in Hungary. Here, András Falus and colleagues describe studies on the control of biosynthesis of complement components and on the nature and function of receptors in the complement system.