. This project will use data collected from a previous study on the natural history of genital HPV in 608 female college students. Questionnaire data, cervical-vaginal lavage for HPV DNA, and serum were collected over a median of thirty months. At that time, it was found that approximately 50% of the women became HPV positive within three years. Among those who had an initial infection, 50% were infected with another HPV type within twelve months of the initial infection. The risk of acquiring HPV infection was related to recent ongoing sexual exposures. Once a young woman had acquired an HPV infection, the infection was mainly short-lived (less than twenty-four months). The risk of having a persistent infection was not dependent on sexual exposure, but on viral type, viral load, and other unknown factors. The goal of this application is to obtain or produce VLP antigens from the most common HPV types in the population. The serum samples obtained from the women will be evaluated for serologic response (IgM and IgG) to HPV VLP antigens in terms of the time from initial HPV infection to the development of antibody, duration of detectable antibody titres, and change in antibody titre over time. To identify viral risk factors related to the development and duration of anti-VLP antibodies, including type-specific HPV infection, viral load, infection with multiple HPV types, duration of HPV infection, and presence of preexisting HPV anti-VLP antibodies to other HPV types, the ability of anti-VLP antibodies to protect and/or modify subsequent HPV type specific genital infections will also be assessed. Seronegative and seropositive individuals will be compared with respect to the incidence of type-specific and total infection, controlling for social and other behavioral risk factors. The study evaluating the serologic response to HPV would add great importance to the HPV research, since little is known at this time. Nine VLPs will be obtained from collaborators and eight of the VLPs will be developed anew. The seventeen selected HPV types have a prevalence of over 5% in their infected population. The L1 coding region of the HPV type will be cloned into Baculovirus expression vectors. Insect cells will be infected with a very high level of production of the L1 protein and formation of the VLPs. The VLPs will be isolated by radiant centrifugation and characterized by transmission electron microscopy and haemagglutination of mouse red blood cells. The haemagglutination assay will be used to evaluate each batch of VLPs to determine the haemagglutination activity per microgram of protein. This will standardize the confirmation epitopes per unit protein so that equivalent amounts of functional antigens are used for each assay. Standardization of the VLP ELISA assay will be performed using validated serum panels.