Inge Fink - Comparative molecular characterization of TOLL-like receptors activated by ß-glucans

My main interests lie in the field of molecular immunology of fish. The immune system is a complex system which, in vertebrates, is composed of cellular and humoral responses. Although teleost fish diverged from the tetrapod lineage about 450 million years ago, their immune system shows considerable conservation with higher vertebrates highlighted by the presence of e.g. orthologous pattern recognition receptors (PRRs) and stimulated cytokines. However, there is also increasing evidence of teleost fish-specific components and functions that are not observed in mammals suggesting complexity and diversity in teleost fish immune function.

Common carp (Cyprinus carpio L.) is one of the oldest domesticated fish species and it has been extensively studied. In terms of gene identification, common carp is being overshadowed by other fish species (e.g. zebrafish, Medaka, Fugu and Tetraodon). However, the publication of the complete genome sequence is expected in the nearest future.

Studies on common carp covering developmental, immunological, aquaculture, genomic and comparative genetic aspects are not only of ‘pure scientific’ interest, but also have strong potential practical applications. European common carp production has steadily increased over the past decades and in 2004 the production of common carp reached 13% of the global freshwater aquaculture (Cultured Aquatic Species Fact Sheets. FAO – Rome). As a result, common carp is a valuable and interesting model organism to study.

Within both the health and agricultural sectors there is now a recognised philosophy that in the control of disease and improvement of general welfare conditions prevention of infection is, on economical and ethical grounds, more appropriate than treatment of disease. Immunostimulation is considered highly effective in increasing disease resistance of fish that are faced with stress factors including infections in aquaculture. Fish treated with immunostimulants show enhanced general immunocompetence. Our data aim to improve the understanding of defence mechanisms in fish and are expected to lead to a more efficient and sustainable control of fish diseases in aquaculture.

In this PhD project I am taking a molecular approach to study the modulation of innate immune responses by β-glucans and focus on pattern-recognition receptors (PRRs) on myeloid cells that respond to pathogen-associated molecular patterns (PAMPs) such as β-glucans that compose fungal cell walls. PRRs that are predicted to be central to this process are Toll-like receptors (TLRs).

The focus of this project is on TLR1 and TLR2 expressed on carp myeloid cells, on the signaling pathways of the TLRs and on their possible functions as activating receptors involved in innate immune responses to, for example, stimulation with β-glucans or infections with parasites (Trypanoplasma borreli). Co-receptors such as the scavenger receptor (SR) CD36 might be involved in the process.

Once TLR and SR sequences are obtained, they will allow for the design of specific primers for real-time quantitative PCR analysis of gene expression induced by β-glucan and parasites. The sequences will also allow for the design of transfection experiments aimed at studying the degree of evolutionary conservation of TLR activation mechanisms in both human cell lines and in carp myeloid cells.