Abstract
Background: Sepsis is still developing exorbitantly high mortality. In response to microbial molecules, T cell activation plays a crucial role in sepsis’s initial innate immune reactions. The imbalance between Th17 and Treg participates in sepsis progression. CD28 signaling pathway was essential for the expression of inflammatory cytokines related to Th17, and play a crucial role in the maintenance of Treg. We investigated the correlations of the balance between Th17 and Treg to prognosis in sepsis patients and influence of anti-CD28 antibody on the ratio of Th17 to Treg in sepsis mice.
Methods: 60 sepsis patients’ baseline conditions were recorded, and the expressions of inflammatory factors in the peripheral blood and levels of procalcitonin (PCT) were detected. PBMCs were separated, subtypes of T cells and related biomarkers were measured by Fluorescence-activated cell sorting (FACS). Furthermore, the relationship between the above indicators and patients’ condition scoring (APACHEⅡand SOFA) and ICU hospitalization time were analyzed. To investigate effects of CD28 on the balance of Th17 between Treg, anti-CD28 antibody was intraperitoneal administrated to cecal ligation and puncture (CLP) mice.
Results: Compared with septic patients who stay in ICU more than 14 days, the Th17/Treg ratio of patients with ICU hospitalization of fewer than 14 days was significantly lower. The sepsis patients with higher expression of CD28 in peripheral blood lymphocytes have lower APACHE II and SOFA scores. Moreover, the expression of CD28 was significantly higher in sepsis patients than that of healthy donors. After administration of CD28 monoclonal antibody, 7-day mortality and clinical score were significantly improved in septic mice, with splenocyte Th17/Treg ratio decreased. CD28 antibody alleviates the expression of pro-inflammatory factors and spleen injury related to apoptosis.
Conclusions: Th17/Treg ratio revealed septic patient severity and can be used as a predictor of ICU stay. CD28 monoclonal antibody could improve 7-day mortality of septic mice by decreasing T cell apoptosis and amending the ratio of Th17/Treg.
Keywords: Sepsis, length of stay in ICU, Th17/Treg, CD28, Risk stratification, Clinical outcomes
Trial registration: CHEC2019-133, CTR20191855.Registered 27 August 2019
Background
Sepsis is a significant public health concern; the estimated number of sepsis cases each year worldwide has doubled compared with previous estimations and is almost 49 million now[1]. Sepsis refers to the life-threatening organ dysfunction caused by the dysregulation of the body’s response to infection, especially immune dysregulation with pro-inflammatory and anti-inflammatory imbalance[2]. The complicated collapsed immune response to severe infection was considered the central pathogenesis of sepsis[3-5].
Meanwhile, immunosuppression also coincides with lymphopenia and loss of immune function. T lymphocytes are one of the critical immune cells with regulating antimicrobial phagocytic and cytotoxic activity. There are many different subtypes T lymphocytes such as naïve T cells, helper T (Th) cells, memory T cells, regular T (Treg) cells (CD4+CD25+ regulatory T cells) and so on with different surface markers, transcriptional regulators, effector molecules and functions. The subtypes of each cell and the ratio between subtypes are different at different stages of T cell immunity[6]. Among such subtypes, Treg and CD4+IL-17+ T helper cells(Th17) share a common precursor cell (the naïve CD4 T cell) and change appearance with the disease progressing[7, 8]. Mice that knocked out the FoxP3 gene, which Treg cell-specific marker controls the T cells development and their regulatory activities, developed fatal inflammatory diseases[9]. Th17, secreting IL-17 and specific transcriptional regulator ROR-γt, plays an essential physiological role at mucosal barriers and is involved in inflammatory responses to pathogens [10]. The balance between Th17 and Treg has emerged as a prominent factor in regulating autoimmunity[11]. Accumulated evidences suggest that the imbalance of Th17 and Treg is associated with the development of many diseases[12], such as primary Sjögren’s syndrome[13], Experimental Autoimmune Encephalomyelitis[14], human graft-versus-host disease[15] and asthma[16].
The ratio of Th17/Treg might become predictors of immune status; the identification and intervention of T cell immune response process in sepsis may be the focus of future treatment. CD28 signal pathway, one of the critical costimulatory molecules on T cells, can active and maintain T cell functions, stimulate the body’s immune response through combining with CTLA-4 and B7(CD80/CD86) molecule on antigen-presenting cells (APC) [17]. CD28 signaling is essential for effector T cells to overcome Treg cell-mediated immunosuppression[17]. CD28 signaling pathway plays a crucial role in maintaining Treg pool size and each Treg subset’s homeostasis by promoting the development and proliferation of these cells [18, 19]. Then we observed the ratio of Th17/Treg in predicting severity and outcomes of septic patients, furthermore as the possible hint of the immunotherapy timing. Effects of CD28 signaling pathway on the balance of Th17/Treg in septic mice need to be identified, then providing a therapeutic reference for sepsis.