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Table 1 Characteristics of included studies (n = 13)

From: Natural killer cell levels in adults living with type 2 diabetes: a systematic review and meta-analysis of clinical studies

Author Country Study design Sample size Age Male n (%) Outcomes
Akesson, 2010 [15] Sweden Cross- sectional 46 T2D
20 Controls
T2D (55.8 ± 43.4)
Control (NR)
38 (83) Patients with T2D had decreased peripheral natural killer (NK) cells compared to controls.
Berrou, 2013 [16] France Cross- sectional 51 T2D
54 Controls
T2D (51.3 ± 14.4)
Control (NR)
33 (65) The levels of NK cells were similar between patients with T2D and healthy controls.
Guo, 2012 [27] China Cross- sectional 16 T2D
9 Controls
T2D (40 ± 35.7)
Control (45 ± 20.4)
9 (56) There was no significant difference in the levels of NK cells between T2D patients and control.
Kim, 2019 [28] S. Korea Cross- sectional 21 T2D, 13 Controls T2D (60.71 ± 6.99)
Control (55 ± 13.76)
8 (38) Patients with diabetes had lower NK cell activity compared with participants with controls. Comparable levels of lipid profiles was reported between T2D and controls.
Lynch, 2009 [35] Ireland Cross- sectional 26 T2D
26 Controls
T2D (45.5 ± 5.8)
Control (42.6 ± 9.8)
7 (27) The levels of circulating NK cells were decreased in T2D compared to controls.
NK cells from T2D, expressed elevated levels of the inhibitory markers NKB1 and CD158b as well as CD69, an activation marker. Comparable levels of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) were observed between T2D patient and control. However, triglycerides levels were higher in T2D group in comparison to controls.
Medellin-Garibay, 2015 [23] Mexico Prospective cohort 18 T2D
24 Control
T2D (45.4 ± 11.4)
Control (35.8 ± 6.6)
9 (50) The levels of NK cells in circulation were similar between T2D and the control.
Patients with T2D had increased levels of triglycerides, total cholesterol and LDL coupled with decreased Levels of HDL when compared to controls.
Simar, 2014 [21] Denmark Cross- sectional 6 T2D,
4 Controls
T2D (44.1 ± 6.5)
Control (34.8 ± 3)
NR There were no significant differences observed in the levels of NK cells between T2D groups and controls.
Nam, 2018 [25] R. Korea Cross- sectional 33 T2D
35 Controls
T2D (61.4 ± 5.9)
Control (57.8 ± 5.3)
21 (64) The level of NK cells and their functional activity were not different between T2D and control groups.
Nekoua, 2016 [24] Benin Cross- sectional 45 T2D
43 Controls
NR 21 (47) The levels of NK cells were comparable between the T2D patients and the controls. Patients with T2D had lower levels of total cholesterol and triglycerides. However, there was no significant difference in LDL levels.
Olson, 2015 [20] USA Cross- sectional 154 T2D
775 Controls
T2D (66.9 ± 9.5)
Control (65.4 ± 10)
84 (55) No significant differences between the levels of NK cells in patients with T2D versus controls.
Piatkiewicz, 2013 [14] Poland Cross- sectional 18 T2D
18 Controls
T2D (53.6 ± 7.0)
Control (52.4 ± 7.0)
9 (50) Patients with T2D had significantly increased levels of NK cells in comparison to the healthy controls. However, the cytotoxic activity of NK cells in T2D individuals was reduced compared to controls.
Singh, 2019 [22] Sweden Cross- sectional 16 T2D,
13 Controls
T2D (64.0 ± 2.0)
Control (61.6 ± 2.9)
NR (70) Patients with T2D and healthy controls had comparable levels of NK cells
Xiaohong, 2018 [19] China Cross- sectional 41 T2D
30 Controls
NR NR Patients with T2D had significantly increased levels of peripheral NK cells compared to controls.
  1. Not reported: NR; T2D: type 2 diabetes; NKB1: natural killer cell inhibitory receptor