Interaction between C3 and IL-2; inhibition of C3b binding to CR1 by IL-2

A novel approach to immunoapheresis of C3a/C3 and proteomic identification of associates

Background

Complement factor C3 represents the central component of the complement cascade and its activation split product C3a plays an important role in inflammation and disease. Many human disorders are linked to dysregulation of the complement system and alteration in interaction molecules. Therefore, various therapeutic approaches to act on the complement system have been initiated.

Methods and Results

Aiming to develop a tool to eliminate C3a/C3 from the circulation, in a first step a high affine murine monoclonal antibody (mAb) (3F7E2-mAb) was generated against complement factor C3 and selected for binding to the C3a region to serve as immunoaffinity reagent. Functional testing of the 3F7E2-mAb revealed an inhibition of Zymosan-induced cleavage of C3a from C3. Subsequently, a C3a/C3 specific 3F7E2-immunoaffinity column was developed and apheresis of C3a/C3 and associates was performed. Finally, a proteomic analysis was carried out for identification of apheresis products. C3a/C3 was liberated from the 3F7E2-column together with 278 proteins. C3a/C3 interaction specificity was validated by using a haptoglobin immunoaffinity column as control and biostatistic analysis revealed 39 true C3a/C3 interactants.

Conclusion

A novel and functionally active mAb was developed against complement factor C3a/C3 and used in a specific immunoaffinity column that allows apheresis of C3a/C3 and associates and their identification by proteomic analysis. This methodological approach of developing specific antibodies that can be used as immunoaffinity reagents to design immunoaffinity columns for elimination and further identification of associated proteins could open new avenues for the development of tailored immunotherapy in various complement-mediated or autoimmune diseases.

Expression of the Third Component of Complement, C3, in Regenerating Limb Blastema Cells of Urodeles

In this study we have shown that complement component C3 is expressed in the regenerating tissue during urodele limb regeneration. C3 was expressed in the dedifferentiated regeneration blastema and in the redifferentiated limb tissues in the axolotl, Amblystoma mexicanum, and in Notophthalmus viridescens. This expression was verified by immunofluorescent staining using an Ab against axolotl C3 and by in situ hybridization with an axolotl C3 cDNA probe. In the early stages of regeneration C3 appeared to be equally present in all mesenchymal cells and in the wound epithelium, whereas in the later stages it was mainly expressed in the differentiating muscle cells. Since no expression was seen in the developing limb, it appears that the C3 expression was specific to the regeneration process. We then demonstrated by hybridization experiments that a blastema cell line of myogenic origin expresses C3. All these findings implicate C3 in the dedifferentiation process and may indicate a new role for this molecule in muscle differentiation.

Effects of decomplementation with cobra venom factor on experimental vasculitis

Mercuric chloride (HgCl2) induces autoimmunity in susceptible rat strains, with hyper-IgE, appearance of a number of autoantibodies, and widespread tissue injury, including necrotizing vasculitis in the gut. In the early phase of tissue injury there is granulocyte infiltration; later there is immunoglobulin deposition along basement membranes in vessels. We have analysed the role of complement in this model using cobra venom factor (CVF), which causes decomplementation lasting around 5 days. The characteristic time course when HgCl2 is given over 10 days is that tissue injury and autoantibody levels reach a peak at around day 15 (start of HgCl2 = day 0). We therefore gave CVF either early (day 0), intermediate (day 5) or late (day 10); a fourth group (controls) received HgCl2 but no CVF. At each time point, CVF caused complete decomplementation which lasted for at least 5 days. Serum IgE and autoantibody levels were similar in all four experimental groups. Tissue injury in the 'early' CVF group and in the 'late' CVF group was not significantly different from controls, but in the intermediate group tissue injury was significantly more severe than in controls. These data indicate that the complement system does not play a major role in the induction of autoantibodies by HgCl2, nor in the effector phase of tissue injury. We speculate that the exacerbation of tissue injury by CVF in the group given this agent at an intermediate stage of the model is explained by the presence of products of C3 activation which have proinflammatory effects during the phase of active granulocyte-mediated tissue injury.

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.

The role of C3 in the immune response

The complement system, particularly the third component, plays an important modulatory role in the inductive phase of the immune response. As discussed here by Anna Erdei and colleagues, the picture that is emerging is that immobilized C3 split products facilitate the cooperation between immunocompetent cells and are co-stimulatory molecules in T- and B-cell activation, probably as a result of their ability to promote cell-cell adhesion. In contrast, soluble C3 products inhibit lymphocyte proliferation.

Complement-mediated inactivation of interferon-gamma in ELISA systems

The recovery of a predetermined amount of interferon-gamma (IFN-gamma) added to normal serum was studied in two independent sandwich ELISA systems specific for rat and human IFN-gamma. In both assays the ELISA activity was rapidly lost in fresh but not in heat-inactivated (30', 56 degrees C) serum. Ninety percent of the initial activity had disappeared within 30 minutes upon incubation at 37 degrees C. Serum-mediated inhibition was not species-specific as the ELISA activity of rat IFN-gamma diminished equally well in rat and human sera. Inhibition was critically dependent on the isotype of the solid-phase monoclonal antibody (mAb) used in the ELISA systems. IgG1 and IgG2a mAbs efficiently inhibited the ELISA activity of IFN-gamma, whereas an IgA mAb was ineffective. The inhibition was not influenced by a wide variety of anti-proteolytic agents but was effectively blocked by anti-complementary substances or treatments directed to the first (C1) and third (C3) component of complement. Our results indicate that activation of the classical pathway of complement (CPC) and the concomitant covalent binding of C3 to the IFN-gamma molecule play a major role in the inhibitory process. It is concluded that reduction of the ELISA activity is attributable to diminished accessibility of the detector antibody for the IFN-gamma protein as a consequence of C3 binding.