Measuring T cell responses to Chlamydia trachomatis in young South African women to characterise immune correlates in the context of HIV risk Rubina Bunjun1,2*, Micaela Lurie1, Shaun Barnabas1,3, Smritee Dabee1,2, Frans Radebe4,6, Venessa Maseko4,6, Ranmini Kularatne4,6, Shameem Z. Jaumdally1, Hoyam Gamieldien1, Heather B. Jaspan1,5, Linda-Gail Bekker1,3, and Jo-Ann S. Passmore1,2,6 1Institute of Infectious Disease and Molecular Medicine, University of Cape Town, South Africa; 2DST-NRF CAPRISA Centers of Excellence in HIV prevention, University of Cape Town, South Africa; 3Desmond Tutu HIV Foundation, University of Cape Town, South Africa; 4National Institute for Communicable Diseases Sandringham, South Africa; 5Seattle Children's' Hospital, Seattle, USA; 6National Health Laboratory Services, South Africa; *Corresponding author Chlamydia trachomatis (CT) is an extremely common bacterial sexually transmitted infection. Studies of South African adolescent girls reported a prevalence of >40% with more than 90% of these infections asymptomatic. Chlamydia infection is a major cause of poor reproductive health outcomes and contributes to HIV risk in young women by causing genital tract inflammation. There is still no vaccine against CT due to factors complicating vaccine development. Although Th1 responses play a role in immune control of CT, robust correlates of protection remain poorly defined. Testing immune correlates by studying T cell responses to chlamydia is challenging, with limited availability of commercial chlamydial antigens. Therefore, we aimed to generate CT antigens to investigate Chlamydia-specific CD4+ T cell memory responses in the context of CT clearance, genital inflammatory potential and HIV infectivity potential. CT serovar E, which was highly prevalent in South African women, was used to infect McCoy cells and blind passaged onto fresh monolayers sequentially until infection of four 6-well plates was achieved. CT elementary bodies were isolated by Renografin density gradient purification. PBMC from CT-infected young women were stimulated with heat killed or lysed CT. The cells were phenotyped and the production of IFN-γ, TNF-α and IL-17 measured by multiparameter flow cytometry. CT-specific CD4+ T cells primarily produced Th1 cytokines and expressed CCR6, associated with genital tract homing potential. These studies are vital in understanding and preventing chlamydia infections, with the ultimate goal of lowering HIV risk in young women.
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