Screening method

Abstract

The invention relates to methods for the identification of novel receptors and/or novel ligands. The invention is based on the concept that parasites have developed a number of biologically active compounds in their saliva to cope with the defense mechanisms of the host organisms on which they feed and to manipulate the biological functions of host molecules to their advantage. These saliva compounds can be used to identify novel molecules within the host systems. Furthermore, these saliva compounds can be used to elucidate the functions of molecules whose existence is already known.

1 . A method for identifying a receptor ligand with a biological function in a host organism, said method comprising the steps of: 
 (a) bringing a sample of biological material from a host organism that is suspected of containing the receptor or ligand into contact with a compound derived from the saliva or salivary glands of a blood-feeding parasite, wherein said sample of biological material is a heterogenous protein preparation selected from the group consisting of a biological fluid such as blood, lymph or cerebrospinal fluid, or a protein expression library such as a wound site library, a lambda wound site expression library or a phage display library; and    (b) isolating from the sample, one or more receptors or ligands that bind to the parasite salivary compound.    
     
     
         2 . A method according to  claim 1 , wherein said sample of host biological material is a tissue, such as blood.  
     
     
         3 . A method according to  claim 1 , wherein said sample of host biological material comprises one or more proteins isolated from the host organism.  
     
     
         4 . A method according to  claim 3 , wherein said one or more proteins isolated from the host organism are produced by recombinant means.  
     
     
         5 . A method according to  claim 4 , wherein said one or more recombinant proteins are generated by expression from a host gene cloned under the control of a heterologous promoter.  
     
     
         6 . A method according to  claim 5 , wherein said one or more recombinant proteins are the products of a gene expression library.  
     
     
         7 . A method according to  claim 1 , wherein said compound derived from the parasite saliva is a protein, peptide or small non-peptide molecule.  
     
     
         8 . A method according to  claim 1 , wherein said sample of host biological material is brought into contact with a preparation of saliva from at least one blood-feeding parasite species.  
     
     
         9 . A method according to  claim 8 , wherein said preparation of saliva is a preparation of salivary extract.  
     
     
         10 . A method according to  claim 9 , wherein said preparation for salivary extract is a fraction of a salivary extract.  
     
     
         11 . A method according to  claim 1 , wherein said sample of host biological material is brought into contact with an expression library derived from the salivary gland of at least one blood-feeding parasite species.  
     
     
         12 . A method according to  claim 1 , wherein said screening method includes a step of affinity purification, antigen panning, plasmon resonance detection, or comprises a competitive binding assay or yeast two hybrid system.  
     
     
         13 . A method according to  claim 12 , wherein either said parasite salivary compound or the biological material from the host organism is tagged to aid the isolation of the host receptor or ligand bound to said parasite salivary compound.  
     
     
         14 . A method according to  claim 13 , wherein said parasite salivary compound is bound to a support, such as a resin.  
     
     
         15 . A method of screening for a gene encoding a receptor or encoding a receptor ligand with a biological function in a host organism, comprising the steps of: 
 (a) bringing a nucleic acid molecule derived from said host organism that is suspected of containing the receptor or ligand into contact with a nucleic acid molecule encoding a molecule present in the saliva or salivary glands of a blood-feeding parasite, under conditions suitable for the hybridization of homologous nucleic acid molecules; and    (b) isolating from the sample, host-derived nucleic acid molecules that hybridize with said parasite nucleic acid molecules.    
     
     
         16 . A method according to  claim 15 , wherein said host-derived and parasite-derived nucleic acid molecules are oligonucleotides of at least 15 nucleotides in length.  
     
     
         17 . A method according to  claim 16 , wherein said screening method is performed using gene array technology.  
     
     
         18 . A method according to  claim 17 , wherein said gene array technology involves the use of gene chips.  
     
     
         19 . A method according to either of claims  1  or  15 , wherein said blood-feeding parasite is a tick, a mosquito, a horsefly or other blood-sucking insect, or a leech or other blood-sucking worm.  
     
     
         20 . A method according to  claim 19 , wherein said tick is an Ixodid ticks such as  Rhipicephalus appendiculatus, Dermacentor reticulatus, Amblyomma variegatum, Ixodes ricinus  and  Ixodes hexagonus , or an argasid tick such as  Ornithodoros moubata.    
     
     
         21 . A method according to either of claims  1  or  15 , wherein said host organism is a bird, reptile, fish or mammal, preferably a human.  
     
     
         22 . A host receptor, ligand or gene identified by a screening method according to either of claims  1  or  15 .  
     
     
         23 . A host receptor, receptor ligand or gene according to  claim 22 , for use as a pharmaceutical.  
     
     
         24 . The method according to either of claims  1  or  15 , wherein the compound derived from the saliva or salivary glands of a blood-feeding parasite is a parasite salivary protein.