This invention relates to the field of biotechnology or genetic engineering. Specifically, this invention relates to the field of gene expression. More specifically, this invention relates to novel substitution mutant receptors and their use in a nuclear receptor-based inducible gene expression system and methods of modulating the expression of a gene in a host cell for applications such as gene therapy, large scale production of proteins and antibodies, cell-based high throughput screening assays, functional genomics and regulation of traits in transgenic organisms.

Provided is a polypeptide composition comprising one or more polypeptides, which polypeptides are immunogenic in a vertebrate such that they cause the vertebrate to produce immune system cells capable of recognizing at least one epitope from an arthropod saliva protein fraction, wherein the arthropod saliva protein fraction has a mass of 40 kDA or less, and wherein the polypeptides are selected independently from: the polypeptide sequences of SEQ ID 1-44 or sub-sequences from these sequences, the sub-sequences having 7 amino acids or more; or from polypeptide sequences having 85% homology or more with one or more of the above sequences and contained in one or more of the following databases: GenBank, Protein Data Bank (PDB), SwissProt, Protein Information Resource (PIR), Protein Research Foundation (PRF), or CDS translations of these.