<b><i>Background:</i></b> Mild cognitive impairment (MCI) induced the majority number of dementia patients. The prevalence of MCI in China varied across studies with different screening tools and diagnostic criteria. <b><i>Objective:</i></b> A systematic review and meta-analysis was conducted to estimate the pooled MCI prevalence among the population aged 55 years and older in China. <b><i>Methods:</i></b> PubMed, EMBASE, CNKI, Wanfang, CQVIP, and CBMdisc were searched for studies on prevalence of MCI among Chinese elderly between January 1, 1980, and February 10, 2020. The quality assessment was conducted via external validity, internal validity, and informativity, the pooled prevalence was calculated through the random-effect model, and the homogeneity was evaluated by Cochran’s <i>Q</i> test and <i>I</i>². <b><i>Results:</i></b> Fifty-three studies with 123,766 subjects were included. The pooled prevalence of MCI among Chinese elderly was 15.4% (95% CI: 13.5–17.4%). Subgroup analyses indicated that the prevalence calculated with different screening tools was 20.2% (95% CI: 15.1–25.9%) for Montreal Cognitive Assessment (MoCA) and 13.0% (95% CI: 10.7–15.5%) for Mini-Mental State Examination (MMSE). According to different diagnostic criteria, the prevalence was 14.8% (95% CI: 12.2–17.6%) for Petersen criteria, 15.0% (95% CI: 12.7–17.5%) for DSM-IV, and 21.2% (95% CI: 17.5–25.2%) for Chinese Expert Consensus on Cognitive Impairment (CECCI). Besides, women, older adults, illiterate people, rural residents, and those who lived with unhealthy lifestyles and morbidity showed higher prevalence. <b><i>Conclusions:</i></b> The prevalence of MCI in China was 15.4%, which varied by demographics, lifestyles, morbidity, screening tools, and diagnostic criteria. In further studies, screening tools and diagnosis criteria should be considered when estimating MCI prevalence.

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The aim of this study is to evaluate the age related changes of T lymphocyte subsets in C57BL/6 mice and immune function. Multi-color immunofluorescence techniques that were used to analyse relative numbers of T lymphocyte subsets include CD4, CD8, naive and memory CD4 and CD8, CD8CD28 T cells in peripheral blood of C57BL/6 mice from different age groups (Group I: 2 months old; Group II: 7 months old; Group III: 21 months old); Splenocytes isolated from different group mice were stimulated with Con A to evaluate the proliferative ability. Compared with group I, group II had a significant reduction in the percentage of CD4, naive CD4 and CD8 T cells and an increase in the percentage of CD8 T cells, while group III had a significant reduction in the percentage of CD4, naive CD4 and CD8 T cells and increase in the percentage of CD8, memory CD4 and CD8 T cells in peripheral blood. Compared with group II, group III had a significant reduction in the percentage of naive CD8 T cells and increase in the percentage of memory CD4 and CD8, CD8CD28 T cells in peripheral blood. The T lymphocyte proliferation in vitro showed that groups II and III had a lower proliferative capacity than group I, between groups II and III, there was not a significant difference. We provide relative values for the T lymphocyte subsets in the different age groups of C57BL/6 mice. The immune system began aging at 7 months old in C57BL/6 mice under a specific pathogen free environment.