Process for producing antigenic substance

A method for screening an antigenic component using a cell-free protein synthesis means with the use of a wheat embryo extract, comprising:

• 1) a step for preparing a gene comprising a region selected within a desired candidate gene,
• 2) a step for synthesizing a mRNA from the gene prepared in step 1),
• 3) a step for synthesizing a polypeptide by a cell-free protein synthesis means with the use of a wheat embryo extract using the mRNA synthesized in step 2) as a translation template, or synthesizing a polypeptide by a cell-free protein synthesis system with an integrated transcription/translation manner using the gene prepared in step 1) as a template,
• 4) a step for immunizing a mammal with the polypeptide synthesized in step 3) to obtain the antiserum,
• 5) a step for reacting the antiserum described above with a desired target microbe or a protein derived from the microbe to analyze the reactivity, and
• 6) a step for identifying the region selected within the candidate gene from which the antiserum has been derived as a candidate antigenic component if the antiserum is confirmed to react.