Differential susceptibility and maturation of thymocyte subsets during Salmonella Typhimurium infection: insights on the roles of glucocorticoids and Interferon-gamma

Abstract

The thymus is known to atrophy during infections; however, a systematic study of changes in thymocyte subpopulations has not been performed. This aspect was investigated, using multi-color flow cytometry, during oral infection of mice with Salmonella Typhimurium (S. Typhimurium). The major highlights are: First, a block in the developmental pathway of CD4−CD8− double negative (DN) thymocytes is observed. Second, CD4+CD8+ double positive (DP) thymocytes, mainly in the DP1 (CD5loCD3lo) and DP2 (CD5hiCD3int), but not DP3 (CD5intCD3hi), subsets are reduced. Third, single positive (SP) thymocytes are more resistant to depletion but their maturation is delayed, leading to accumulation of CD24hiCD3hi SP. Kinetic studies during infection demonstrated differences in sensitivity of thymic subpopulations: Immature single positive (ISP) > DP1, DP2 > DN3, DN4 > DN2 > CD4+ > CD8+. Upon infection, glucocorticoids (GC), inflammatory cytokines, e.g. Ifnγ, etc are induced, which enhance thymocyte death. Treatment with RU486, the GC receptor antagonist, increases the survival of most thymic subsets during infection. Studies with Ifnγ−/− mice demonstrated that endogenous Ifnγ produced during infection enhances the depletion of DN2-DN4 subsets, promotes the accumulation of DP3 and delays the maturation of SP thymocytes. The implications of these observations on host cellular responses during infections are discussed.

Comparative analysis of thymic subpopulations during different modes of atrophy identifies the reactive oxygen species scavenger, N‐acetyl cysteine, to increase the survival of thymocytes during infection‐induced and lipopolysaccharide‐induced thymic atrophy

“…The various cell populations in the thymi were studied using multicolour flow cytometry. The panel of antibodies used to analyse the thymocyte subpopulations were standardized in a previous study from our laboratory . Briefly, the thymocytes were kept for 45 min at 4° with the mentioned antibodies specific to cell‐surface markers.…”

“…Numerous markers including CD24 and CD3 and CD69 and CD62L have been used to study the SP cells at different stages of maturation. For example, the CD24 hi CD3 hi and CD24 int CD3 hi cells are the more immature cells in the SP subset, whereas the CD24 lo CD3 hi are comparatively more mature . Naive CD4 + and CD8 + T cells egress the thymus after maturation of SPs.…”

“…In spite of the phenomenon of thymic atrophy being widely studied in mouse models, comparative and detailed investigations on the major thymocyte subpopulations have not been performed. Our laboratory has studied distinct infection‐induced changes occurring in the major thymocyte subpopulations during Salmonella Typhimurium infection‐induced thymic atrophy in C57BL/6 mice . The broad questions that we asked in this study were whether there are differences in subpopulations during various modes of thymic atrophy, namely, treatments with LPS (inflammatory but non‐infectious), Eto (drug used to treat different cancers) and Dex (clinically used to treat several inflammatory diseases) in BALB/c mice, using multicolour flow cytometry.…”

“…The S . Typhimurium‐induced thymic atrophy model (inflammatory and infectious) previously standardized in our laboratory served as a useful control. Distinct differences were observed in the thymocyte subpopulations in all the thymic atrophy models studied.…”

Salmonella infection: Interplay between the bacteria and host immune system

“…Interestingly, while Salmonella also infects the thymus and induces thymic atrophy, mature CD4 T cell output is largely unaffected [126]. Conversely, double negative (DN; CD4-CD8-) thymocyte populations do appear to be reduced during both acute and chronic thymic infection by Salmonella [127]. In this same study, single positive (SP; CD4+ or CD8+) numbers were largely unaffected; however, it did appear these cells were somewhat more immature, possibly because they had only recently committed to the SP lineage to compensate for the loss of DN cells.…”