Consider Syphilis in Case of Lymphopenia in HIV-Infected Men Who Have Sex with Men (MSM): A Single-center, Retrospective Study

Introduction: The way syphilis affects the immunologic and virologic parameters of a human immunodeficiency virus (HIV) infection remains controversial. The aim of this study was to investigate the impact of syphilis infection on lymphocyte and lymphocyte subset counts as well as viral load in HIV-infected patients. Methods: All HIV-infected patients attending the outpatient clinic for infectious diseases of Hannover Medical University Hospital diagnosed with syphilis between 2009 and 2016 were retrospectively evaluated for changes in total lymphocyte, B cell, CD3(+) T cell, CD4(+) and CD8(+) T cell counts as well as in HIV viral load. These parameters were assessed at three different time points, i.e., 3-6months before, at diagnosis and 3-6months after treatment of syphilis. Results: Eighty-four HIV-infected patients, all with early syphilis, were identified. The vast majority were men who have sex with men (MSM), and 80% were receiving antiretroviral therapy (ART). Syphilis was associated with a significant reduction in the total lymphocyte count and counts of all studied lymphocyte subsets, including CD4(+) T cells, whose percentage among lymphocytes did not change. No significant changes in HIV viral load were observed at any of the studied time points. Further, antibiotic treatment of syphilis restored lymphocyte counts back to pretreatment levels. Conclusion: Syphilis induces a relative non-CD4(+) T cell-specific lymphopenia in HIV-infected patients. Our data suggest that serologic testing for syphilis should be considered in HIV-infected MSM in case of an otherwise unexplained drop in total lymphocyte count.