In addition, we cannot determine whether women who were HPV16 DNA-negative were actually exposed, although the numbers of recent sexual partners were the same in the infected and non-infected groups . contamination (OR?=?0.48, CI?=?0.27C0.86, compared with seronegatives). Compared with seronegatives, the highest seropositive tertile antibody levels from the direct ELISA (OR?=?0.53, CI?=?0.28C0.90) as well as the SEAP-NA (OR?=?0.20, CI?=?0.06, 0.64) were also significantly associated with protection from HPV16 contamination. Conclusions/Significance Enrollment HPV16 seropositivity by any of the three serological assays evaluated was associated with protection from subsequent contamination, although cutoffs for immune protection were different. We defined Dexmedetomidine HCl the assays and seropositivity levels after natural contamination that better measure and translate to protective immunity. Introduction Contamination with carcinogenic human papillomaviruses (HPV), most notably types 16 and 18, is necessary for the development of cervical malignancy , the third most common malignancy in women worldwide . While contamination with HPV is quite common, with the lifetime incidence estimated to be 80% , most infections become undetectable within 1C2 years . Only a small fraction of infections with high-risk HPV fail to clear, resulting in overt HPV persistence . Prolonged HPV infection is usually strongly associated with the development of cervical intraepithelial neoplasia grade 3 (CIN3), which progresses to invasive cervical malignancy in a minority of cases . Immune responses generated upon HPV contamination are likely to be a critical mechanism for preventing, controlling, and eliminating HPV contamination . Characterization of the immune responses to HPV virions can help explain how prior contamination or immunization protects against future infection and associated disease. Correlates of protection are currently still unclear. Neutralizing antibodies are expected to be the primary immune mechanism for protection against HPV contamination . Because of the role of antibodies in preventing HPV infections, serological assays are important for measuring the antibodies or other immune factors directed against HPV, and these assays may identify the individuals who experienced mounted an immune response to previous exposure to HPV and may be guarded against subsequent HPV contamination . Serological assays for HPV16 based on different biochemistry include Dexmedetomidine HCl the competitive Luminex immunoassay (cLIA), designed to measure antibodies against a specific neutralizing epitope ; the secreted alkaline phosphatase neutralization assay, designed to measure overall neutralizing potential, (SEAP-NA) ; and the virus-like particle (VLP)-based enzyme-linked immunosorbent assay Keratin 7 antibody (ELISA), designed to measure a broad spectrum of neutralizing and non-neutralizing antibodies directed against the L1 capsid protein . Each assay provides only a partial characterization of immune status, and comparison of seroprevalence across assays is usually complicated because the assays differ quantitatively, i.e., by throughput and detection range, and qualitatively, i.e., whether they detect antibodies against multiple epitopes, which may be indicative of previous exposure, or neutralizing antibodies that may confer immune protection. Immune responses to HPV measured by currently available assays may or may not predict individual protection , but limited work has been carried out to determine if any measured immune response can define immediate or future protection against HPV contamination or associated disease , , . Safaeian et al. showed that women who have the highest seropositive tertile of HPV16 and HPV18 antibody levels based on a VLP-based direct ELISA assay are significantly protected from subsequent contamination with HPV16 and HPV18, respectively , after controlling for risk factors associated with newly detected HPV contamination. Due to the potential for serological assays to differentially measure HPV antibody levels in association with protection from subsequent HPV contamination, we compared the previous HPV16 results obtained using a VLP-based direct ELISA with results obtained using a VLP-based cLIA and a SEAP-NA. Here, we aimed to identify the assays and seropositivity levels after natural contamination that better measure and Dexmedetomidine HCl translate to protective immunity. Materials and Methods Study Population We selected serum samples obtained at enrollment visit prior to vaccination from women in the control arm of the Costa Rica HPV16/18 Vaccine Trial (CVT), a publicly funded, randomized trial of the efficacy of the HPV16/18 vaccine manufactured by GlaxoSmithKline (GSK).