In mice immunized against GP1,2 in the presence of sGP, an immunization strategy designed to simulate antigen exposure during natural infection, we observed that most resulting anti-GP1,2 antibodies were cross reactive with and thus susceptible to competition by sGP, even though the titers of anti-GP1,2 antibodies in these mice were similar to the titers in mice immunized against GP1,2 alone. This evidence concerns the gene GTPBP1 and infection.