Interrogating infant immune responses for diagnosis of congenital syphilis infection - ABSTRACT Syphilis infection remains endemic among adults worldwide. Rates are rising among women of childbearing age in the U.S., resulting in a concomitant increase in congenital syphilis cases. Untreated congenital syphilis can result in permanent neurologic impairments and osteoarticular deformities. Although some infants have clinical symptoms at birth, many are asymptomatic at delivery. For these asymptomatic, syphilis-exposed infants, diagnostic testing does not reliably identify those with true congenital infection. Because of this, a large number of syphilis-exposed infants undergo extensive diagnostic testing, are treated with antibiotics, and require long- term outpatient follow-up. Tests to discriminate infected infants from those who are exposed but uninfected are necessary to improve clinical management. Our group has a longstanding interest in congenital cytomegalovirus (CMV) infection, and we have shown that infants with congenital CMV infection have evidence of global immunologic activation in peripheral blood that differs markedly from the naïve immune signatures of uninfected neonates. These differences encompass the whole blood transcriptional profiles, differentiation and activation of innate and adaptive immune cell subsets, and serum cytokine profiles. Importantly, the immune profile of congenital CMV is observed among both symptomatic and asymptomatically infected infants and is significantly different from uninfected infants. Human immune responses to congenital syphilis infection are largely unstudied, but responses in adults and animal models show monocyte activation and sustained B and T cell responses. In this project we will test the hypothesis that infants with congenital syphilis infection express markers of global immune activation that distinguish them from healthy, uninfected infants and syphilis-exposed, uninfected infants. Aim 1 will identify characteristics of innate and adaptive immune responses to congenital syphilis among an established cohort of infants with symptomatic congenital syphilis infection using advanced CITE-seq and flow cytometry immunophenotyping methods, which will greatly expand our limited understanding of congenital syphilis immunopathogenesis. Leukocyte markers expressed during congenital syphilis infection will then be applied to an enrolled cohort of asymptomatic, syphilis-exposed infants to determine if these immunologic signatures can distinguish their likelihood of having congenital infection. Aim 2 will establish serum cytokine and chemokine profiles induced by congenital syphilis and apply this profile to asymptomatic, syphilis- exposed infants to discern their likelihood of congenital syphilis infection. As an exploratory objective, biomarkers from Aims 1 and 2 will be synthesized to generate an immune profile for likelihood of congenital infection among asymptomatic, syphilis-exposed infants that can be tested in future studies. Together, these data will provide new insights into the immunopathogenesis of congenital syphilis infection and seek to identify potential biomarkers to discern likelihood of congenital infection among asymptomatic, syphilis-exposed infants.
