A soluble rubella E1 antigen variant is disclosed that comprises amino acids 334-409 of the native rubella E1 peptide, but lacks the C-terminal end and at least the transmembrane region and the anchor segment as well as at least the amino acids 143 to 164. Also described is a recombinant DNA molecule encoding the rubella E1 antigen 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, also disclosed is 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.