Immune surveillance of activated immune and tumour cells by surfactant protein D

Abstract

Surfactant protein D (SP-D) is a carbohydrate/charged pattern recognition molecule of the innate immune system. By virtue of its ability to recognize an array of carbohydrate patterns on the surface of a range of pathogens, SP-D can bring about opsonisation, enhanced phagocytosis and killing of a diverse range of viruses, bacteria and fungi. In addition to antimicrobial functions, which also includes bacteriostatic and fungistatic properties SP-D has also been shown to bind allergens derived from a number of sources including house dust mite, Aspergilllus fumigatus and pollen grains. SP-D allergen interaction leads to inhibition of specific IgE binding and subsequent downregulation of histamine release from sensitized basophils and mast cells. Thus, a number of murine models of pulmonary hypersensitivity and allergic asthma induced by ovalbumin, house dust mite and Aspergillus fumigatus allergens/antigens have been tested for the ability of SP-D to dampen allergic symptoms on the immunological parameters. In general, treatment of allergic models with a recombinant fragment of human SP-D (rh SP-D; composed of trimeric, neck and carbohydrate recognition domain) has been shown to cause downregualtion of specific IgE synthesis, pulmonary and peripheral eosinophilia and airway hyper reactivity, and Th2→Th1 polarisation. However, therapeutic alleviation of eosinophilia by rh SP-D treatment became evident when SP-D gene deficient mice were found to be hypereosinophilic In fact, rhSP-D binds well to eosinophils derived from allergic patients and induces apoptosis without affecting eosinophils derived from healthy individuals or non-activated/non-sensitized eosinophils. Proteomic analysis of rh SP-D treated eosinophillic cell line that revealed that apoptosis induction takes place via p53 pathway. In this thesis, proteomic signatures were replicated using a leukemic cell line AML14.3D10 via qPCR analysis by identifying targets from a spectrum of genes, which were either upregulated or downregulated. It appears that in spite of induction of apoptosis by rh SP-D, different cells respond differentially at molecular levels (Chapter 3). Sensing that SP-D can induce apoptosis in altered or transformed cells; the effect of SP-D gene expression within pancreatic cancer cells was also investigated. The experiments confirmed p53 pathway dependence for suppression of cancer. Interestingly, factors responsible for metastasis for cancer are also downregulated by endogenous overexpression of SP-D, as validated by wound healing assay. We conclude that SP-D is a general immunosurveillance molecule, which is involved in the clearance of altered and transformed cells (Chapter 4). Chapter 5 shows a direct interaction between DC-SIGN and rh SP-D that inhibits DC-SIGN interaction of allergens and HIV-1, tow common ligands for SP-D and DC-SIGN. Using transfected human embryonic kidney (HEK) cells expressing surface DC-SIGN, we found that pre-treatment of these cells with rhSP-D suppressed DC-SIGN mediated transmission of HIV-1to co-cultured PBMCs. The effect of rhSP-D-DC-SIGN In conclusion, this thesis highlights a broader immune role of SP-D in homeostasis and probably assigns potential functions of extrapulmonary and/or locally synthesized SP-D within non-lung tissues and blood.