The present invention relates to a soluble Rubella E1 antigen and variants of this peptide characterized by lacking at the C-terminal end at least the transmembran region and the anchor segment as well as at least the amino acids 143 to 164 and containing at least the region spanning the disulfid-bridges Cys 349 - Cys 352 and Cys 368 - 401 whereas the N-terminus (Cys 349) of this region contains additionally at least 15 amino acids and / or the C-terminus (Cys 401) of this region contains additionally at least 8 amino acids of the adjacent Rubella E1 antigen sequence.
The region spanning the disulfid-bridges Cys 349 - Cys 352 and Cys 368 - 401 contains at the N-terminus of this region (Cys 349) additionally at least 25, 30, 34 amino acids and / or at the C-terminus (Cys 401) of this region additionally at least 10, 11, 15, 25, 35 amino acids of the adjacent Rubella E1 antigen sequence.
Furthermore, the invention relates to a recombinant DNA molecule, encoding a Rubella E1 antigen and variants, which are recombinantly expressed as a chaperone fusion-protein, refolded into a soluble and immunoreactive conformation and further used for the serological detection of anti-Rubella antibodies. In addition, the present invention discloses a method for the detection, determination and quantification of anti-Rubella antibodies of IgG and / or IgM subclass in a sample wherein the Rubella E1 antigen is used as a capture reagent and / or binding partner for the antibodies. The invention comprises further a diagnostic test and a reagent kit for the detection of anti-Rubella antibodies, containing at least one antigen of the Rubella E1 antigens.