The present invention provides: a novel antiviral agent containing a human antibody κ light chain, a novel human abzyme containing a human antibody κ light chain; a polynucleotide, a vector, and a transformant, each of which relating to the containing a human antibody κ light chain of the above; a primer set for effectively obtaining a human antibody κ light chain having a function as an antiviral agent or abzyme; and a method for producing a polynucleotide and a method for producing a polypeptide, each of which method utilizes the primer set.