High-throughput profiling of the IgG and IgA response to the <i>Treponema pallidum</i> subsp. <i>pallidum</i> proteome in syphilis patients

ABSTRACT Syphilis continues to be a significant global health concern. To define the extent of the IgG and IgA antibody reactome in patients with syphilis and identify reactive antigens and reactivity patterns that could facilitate early diagnosis and possibly serve as biomarkers for treatment response and staging, we developed a pan-proteomic microarray carrying 98.8% (1,009 antigens) of the annotated polypeptides of two Treponema pallidum subsp . pallidum strains (Nichols and SS14). In this study, we probed the array with 217 sera collected pre- and post-treatment from 122 syphilis patients to detect IgG and IgA antibodies. Although a minimal IgA response to T. pallidum antigens were detected in these sera, with only 21 reactive targets on the array, corresponding to 20 T. pallidum antigens, significant IgG reactivity was detected to a total of 104 array protein spots, corresponding to 101 T. pallidum antigens, and roughly encompassing 10% of the pathogen’s proteome. No targets were differentially recognized in pre-treatment sera when factoring in covariates such as syphilis stage, syphilis history, and human immunodeficiency virus status, but a significant decrease in reactivity to 82 antigens was detected in the sera collected post-treatment compared to sera collected at diagnosis. This work helped define the extent of the IgG and IgA antibody response in syphilis patients and identified antigens that could be further evaluated to improve treponemal serological tests. Antigens inducing a detectable IgA response in adults, albeit very few, could be further investigated as diagnostic markers. IMPORTANCE This investigation improved our understanding of the IgG and IgA humoral response to virtually all proteins of Treponema pallidum subsp. pallidum ( T. pallidum ) during natural infection in patients with active and treated syphilis. Using samples collected pre- and post-treatment from individuals presenting with syphilis at different stages, human immunodeficiency virus status, and history of recurrent infection, we identified antigens that could be further investigated to improve early syphilis and congenital syphilis diagnosis and serve as possible biomarkers to monitor treatment response.