Molecular recognition and regulation of the lectin pathway of complement activation

The complement system is a fundamental part of the mammalian immune system, neutralising potentially harmful bacteria, viruses and parasites. A relatively poorly understood branch of this system, called the lectin pathway, relies on recognition of carbohydrates on the surfaces of invading microorganisms to initiate the complement cascade. The lectin pathway is particularly important in the early stages of infection, before specific antibodies can be synthesized by the host or when the immune system is suppressed, for example during HIV infection or following chemotherapy. It kills pathogens directly and also stimulates and directs other parts of the immune system to generate an appropriate response. Although the lectin pathway normally has a protective role, under certain conditions, it can cause severe damage to host tissues. For example, lectin pathway dependent complement activation is believed to cause substantial cardiovascular damage following restoration of blood flow following myocardial infarction. In this grant proposal, we aim to develop a better understanding of the lectin pathway of complement activation by studying the way in which the components interact with each other to initiate and regulate the reaction cascade. We have already established methods for producing key elements using recombinant DNA technology, so that their mode of action can be investigated in a systematic way. Using the results from these studies, we plan to develop specific inhibitors to lectin pathway activation. These inhibitors will be useful tools to help us understand the role of the lectin pathway in complex biological processes and will also serve as potential drugs for the treatment of diseases, including heart and kidney disease. An additional goal of this project is to change the properties of components of the lectin pathway so that they bind to carbohydrates that are present on the surfaces of tumour cells but are not normally found on healthy tissues. We will test the abilities of these modified components to stimulate the immune system to neutralize tumour cells. The knowledge provided by our research will be translated to the scientific community through publication in high quality scientific journals and by presentations at international conferences. Our research will be communicated to the general public through the University and Departmental Web pages via the University Press Office. In particular, important discoveries will be published in the bimonthly University newletter and in the Annual Report, which highlights major achievements of the University.

The goal of the proposed work is to understand how molecular interactions regulate the function of the lectin pathway of complement activation. The results of this study are expected to be of significance to both basic and therapeutic applications. Understanding the fundamental issues of recognition in complement activation has general practical applications in protein engineering and for the design of inhibitors of macromolecular interactions. Biochemical and structural approaches are specifically designed to identify detailed interaction and structural information for MBL-MASP and ficolin-MASP interactions. Based on these studies, short constrained peptide mimics of bioactive protein surfaces will be developed, synthesized and characterized. The peptide mimics will serve as specific inhibitors of lectin-MASP interactions, providing a novel set of reagents to dissect the complex pathways that these proteins mediate. In addition these compounds represent potential first generation therapeutic agents for complement-mediated host damage, including reperfusion damage to myocardium, kidney and other tissues. We also plan to use our knowledge of lectin-carbohydrate interactions to engineer novel lectin-specificities into the framework of MBL and ficolins, thereby altering target specificity whilst retaining the ability to activate complement and stimulate the host?s immune system. By targeting sugars commonly found on tumour cells but rarely associated with healthy cells, we aim to develop a range of immunologically active reagents that are selective for diseased tissues.