Human Papillomavirus (HPV) infections are widespread in the general population. Upon natural HPV infection, seroconversion occurs only in 50-70% of infected women and 4-36% of infected men. With increasing immunisation, it is essential to monitor antibody levels to inform effectiveness of vaccine. Additionally, measuring antibody titres provides an alternative method of assessing HPV infection and immune response as a biomarker for disease.
The objective of this study was to assess the presence and compare the titre of anti HPV16 L1 antibodies in serum, dried blood spots and liquid based cytology (LBC) samples from unvaccinated women.
A prospective sample collection from unvaccinated women attending the NHS Lothian Colposcopy clinics after a diagnosis of cytological abnormality was performed. Ethical approval was obtained from Scotland A Research Ethics Committee (REF 12/SS/0034). Whole blood and LBC samples were collected from 94 women and blood was spotted in Guthrie spot filter papers. Genotyping was performed using the Optiplex HPV Genotyping Kit (Diamex GmbH). Anti HPV16 IgA and IgG was measured in serum, blood spots and LBC from 94 women. Antibody avidity assay was done using Guanidine Hydrochloride and avidity index (AI) was calculated. Linear regression analysis was performed for correlation between IgA and IgG levels within and between each medium of sample.
Linear regression analysis established a significant correlation between the levels of IgG and IgA HPV 16 anti-L1 antibodies in the serum and in blood spot eluates of the patients. There were also significant correlations between serum and dried blood spot eluates for the levels of IgG and IgA for each individual. There was a strong correlation between the levels of IgG and IgA anti-HPV16L1 antibodies in the LBC samples but there was no correlation with serum levels from the same women for either IgG or IgA. There was no correlation between the levels of antibodies and biopsy grade for serum, blood spots or LBCs. There was a range in levels of anti L1 specific antibody in the cohort of women assessed but serum from women infected with alpha 9 types of HPV showed higher values of both IgG and IgA compared to those infected with other types. The average AI in the sample set tested was 0.35 (95% CI 0.25- 0.45)
Our study shows that HPV-16 IgA and IgG antibodies detected in unvaccinated women correlate represent current infection type but have a low avidity. Also, blood spots can be successfully used to detect HPV-16 antibodies. This has implications in low resource settings and population wide surveillance studies aimed at investigation of antibody levels.