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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