In the last few decades, sepsis has been recognized as an important complication of critical illness, which was associated with considerably high morbidity, mortality and increased medical costs [13]. The development of AKI during sepsis further increases morbidity and mortality [14]. Therefore, early diagnosis of AKI and appropriate adjustment of follow-up treatment strategy are very important to improve the prognosis. 2012 KDIGO guideline for AKI present the most recent consensus definition, which was based on increases in serum creatinine or decreases in urine output [12]. However, serum creatinine and urine output have some limitations. On one hand, the definition that relies on change in serum creatinine is establishing a baseline serum creatinine. No consensus method exists to establish pre-AKI baseline serum creatinine in the absence of previous values (recent or distant). One the other hand, it requires the results of change in serum creatinine which needs at least two days, and changes in serum creatinine are often delayed owing to renal reserve and the kinetics of AKI [15]. In addition, the use of diuretics resulted in insignificant changes in urine volume. Therefore, newer methods are needed to detect AKI in sepsis patients. Lymphocyte subtyping is an appropriate method because of the ease of collecting peripheral blood samples and the short duration of results available.
In our study, a total of 171 sepsis patients were included. Among them, 137 patients developed AKI with a median age of 87 years. Flow cytometry analysis showed that the percentages of total T lymphocyte (CD3+), CTL (CD3 + CD8+), and totally activated T lymphocyte (CD3 + HLADR+) were lower in sepsis patients with AKI than in those without AKI. Univariate logistic regression analysis found that percentages of total T lymphocyte, CTL, and totally activated T lymphocyte were protective factors for AKI. And multivariate analysis indicated that percentage of totally activated T lymphocyte was an independent protective factor for AKI. Moreover, ROC analysis showed that total T lymphocyte, CTL, and totally activated T lymphocyte had discriminatory abilities for SA-AKI.
AKI is common in sepsis, a prospective cohort study of 1177 sepsis patients from 198 ICUs in 24 European countries reported a 51% incidence of AKI [16]. Bagshaw SM et al found that 64.4% of patients with septic shock developed early AKI [17]. In contract, our data showed that the incidence of SA-AKI was 80.1%, which was higher than previously reported. The reason may be that our patients were older, with a median age of 86 years, while the median ages of patients in the above study were 65 and 62 years old, respectively. Furthermore, Bagshaw SM et al showed that the age of SA-AKI patients was older than that of non-SA-AKI patients (P < 0.05) [17]. These results suggest that elderly patients with sepsis are more likely to develop AKI.
CD3 is the characteristic surface marker of mature T lymphocytes and total T lymphocyte is defined by marker of CD3. Sepsis often results in an immunosuppressed state [18], Monserrat J showed that CD3 + T lymphocyte was significantly lower in patients with septic shock [19]. Furthermore, Drewry AM reported that persistent lymphopenia was associated with poor outcome in sepsis patients [20]. In this study, our results revealed that SA-AKI patients had lower percentage of total T lymphocyte than that of non-SA-AKI patients with novelty. Moreover, we found that total T lymphocyte was a protective factor for SA-AKI and ROC analysis showed it had discriminatory ability for diagnosis of SA-AKI. These evidences indicated decreased total T lymphocyte was associated with AKI induced by sepsis and could be an immune marker to early diagnose SA-AKI.
CD4 + T lymphocyte (T helper) and CD8 + T lymphocyte (CTL) are the two major types of T lymphocytes involved in the cell-mediated immunity [21]. There are many studies on their role in ischemic AKI, but their role in SA-AKI is less. One study showed that SA-AKI was driven through IL-17 released by CD4 + T lymphocyte. However, our data found that impaired T helper does not mediate the occurrence of AKI or play a protective role. More research is needed to explore the role of T helper in SA-AKI. In addition, our study found that the CTL percentage was significantly lower in sepsis patients with AKI than in those without AKI. We originally reported CTL was impaired in sepsis associated AKI, thus CTL could be a new immune marker of SA-AKI. Previous studies reported that CTL apoptosis was rapidly increased in blood of patients in septic shock, which lead to a profound and persistent lymphopenia associated with poor outcome [22, 23]. Singbartl K et al showed that dysfunction of immune cells can contribute to immune dysfunction and impaired bacterial clearance during AKI [24]. Moreover, one study reported that few T lymphocytes were seen in human kidney biopsy specimens during AKI [21]. These results are consistent with ours, and together they indicate that SA-AKI is closely related to the level and function of CTL.
Totally activated T lymphocyte is charactered by expression of HLADR, which has mainly been regarded as a marker of activated T lymphocytes [25]. HLA-DR molecules play a vital role in the specific immune response to infection. We found that totally activated T lymphocyte of SA-AKI patients was lower than those of sepsis patients without AKI, and it is also a protective and predictive factor for SA-AKI. A previous study showed that HLADR expression on circulating T lymphocyte was reduced in patients with severe sepsis [26]. These data suggested that totally activated T lymphocyte may play a protective role in SA-AKI and may contribute to diagnosis of SA-AKI.
Regulatory T lymphocytes, which are mainly derived from thymus, are considered to be an indispensable part of the regulation of the immune system, and CD25 + is an important marker [27]. Moreover, CD69 + is an early activation marker and involved in the regulatory function of T lymphocyte. Therefore, early activated T lymphocyte (CD69 + T lymphocyte) considered to be a new subset of regulatory T lymphocytes [28]. It has been reported that CD25 + and CD69 + lymphocytes were significantly increased in sepsis [29]. One study showed that soluble CD25 is increased in patients with sepsis induced AKI [30]. But few studies have analyzed the relationship between CD69 + lymphocytes with AKI. Our study found that SA-AKI was not associated with CD25 + and CD69 + lymphocytes. Therefore, more studies are needed to investigate the roles of them in AKI.
Our study has certain limitations. Firstly, this was a retrospective study. Secondly, the relationship between AKI severity and T lymphocyte was not explored. Further studies should be carried out to explore these results.