To assess the extent of sequence and antigenic diversity in the minor capsid proteins (L2) of human papillomavirus (HPV) types 6 and 16, 24 clinical samples were obtained, and the regions encoding the immunodominant epitopes 6U3 and 16REx were amplified by polymerase chain reaction, sequenced, cloned into pATH plasmids, and tested for reactivity with human sera. Two of 11 HPV-6 DNAs were identical to the prototype strain in the 6U3 region, while 9 variants had a G to A transition at nt 5020, changing a valine residue to isoleucine. Of 16 sera that did not react with the prototype HPV-6 L2 fusion protein, 2 reacted with the 6U3-isoleucine variant, and all 8 sera that reacted with the prototype also reacted with the variant. Twelve of 13 HPV-16 DNAs were identical to the prototype strain in the 16REx region, while 1 variant had a C to G transversion at nt 4825, changing a proline to an arginine, but not affecting antigenicity.
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