Background Chlamydia pneumoniae causes respiratory infection in adults and children. Previous studies in our laboratory identified significantly higher in vitro T lymphocyte responses to C. pneumoniae in children with asthma compared to healthy controls which may indicate the presence of T effector memory (TEM) lymphocytes. Aim In the present study, healthy subjects were screened for the presence of TEM cells and their cytokines. CCR7 negative effector TEMs may indicate persistent infection with C. pneumoniae . Methods Peripheral blood mononuclear cells (PBMC) (1×10 6 /mL) from adult non-asthmatic subjects were infected for 1h ± C. pneumoniae TW-183 at a multiplicity of infection (MOI) = 0.1 and cultured (48 hrs). Distributions of lymphocytes (CD4+, CD8+) and TEM cells (CD4+CCR7+CD45RA+CD154+, CD8+CCR7+CD45RA+CD154+) were determined. Levels of intracellular interleukin (IL)-2, IL-4, and interferon (IFN)-gamma were measured (flow microfluorimetry); IFN-gamma was measured in supernatants (ELISA). Results C. pneumoniae infection led to a decrease in numbers of CD8+ TEM and CD8+CD154+ cells; CD4+TEM and CD4+CD154+ cells did not change. Numbers of TEM cells (CD4+IL-2+, CD8+ IL-2+) also decreased. However, number of TEM cells (CD4+IL4-+, CD8+ IL-4+) and (CD4+ IFN-gamma+, CD8+IFN-gamma+) did not change. When stratified according to IFN-gamma+ status, numbers of CD4+ IL-2+ and CD4+IL-4+ TEMs increased; CD8+IL-2+ and CD8+ IL-4+ TEMs decreased. Conclusion C. pneumoniae -induced PBMC IFN-gamma+ responses increased numbers of CD4+ IL-2+ and CD4+IL-4+ TEM cells, while CD8+IL-2+ and CD8+IL-4+ TEMs decreased. Production of IFN-gamma by C. pneumoniae infected PBMC should be further studied as a biomarker of persistent infection in humans.

Coronavirus disease-2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may have a direct effect on several endocrine glands, including the thyroid. 1 SARS-CoV-2 enters cells using the angiotensin-converting enzyme-2 (ACE-2) receptor, expressed by the thyroid. 2 Prior literature reported low levels of triiodothyronine (TT3) and thyroid stimulating hormone (TSH) in adult patients with COVID-19. 3 However, levels of TSH in children during the pandemic are unknown. The aim of this study was to identify

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Chlamydia pneumoniae causes respiratory infection in adults and children. Previous studies in our laboratory identified significantly higher in vitro T lymphocyte responses to C. pneumoniae in children with asthma compared to healthy controls which may indicate the presence of T effector memory (TEM) lymphocytes. In the present study, we screened healthy subjects for the presence of TEM cells and their cytokines. CCR7 negative effector TEMs may indicate persistent infection with C. pneumoniae. METHODS: Peripheral blood mononuclear cells (PBMC) (1310 6 /mL) from adult non-asthmatic subjects (N55) were infected or mock-infected for 1h +/-C. pneumoniae TW-183 at a multiplicity of infection (MOI) 5 0.1 or 0.01 and cultured for 48 hrs. Distributions of lymphocytes (CD4+, CD8+) and TEM cells (CD4+CCR7+CD45RA+CD154+, CD8+CCR7+CD45RA+CD154+) were determined. Levels of intracellular Interleukin (IL)-2, IL-4, and Interferon (IFN)-gamma were measured (flow microfluorimetry). RESULTS: C. pneumoniae infection (48 hr) led to a decrease in numbers of CD8+ TEM and CD8+CD154+ cells (50%, 33%, respectively); numbers of CD4+TEM and CD4+CD154+ cells did not change. In addition, numbers of TEM cells (CD4+IL-2+, CD8+ IL-2+) decreased (;27%, 50%, respectively). However, number of TEM cells (CD4+IL4-+, CD8+ IL-4+) and (CD4+ IFN-gamma+, CD8+IFN-gamma+) did not change significantly (P<0.05). CONCLUSIONS: C. pneumoniae infection decreased CD4+ and CD8+ IL-2+ TEM cells in this study population. These findings may provide more understanding of the mechanisms of persistent C. pneumoniae infection.