Data sources and search strategies

Science Citation Index-Expanded (SCI-E) of Thomson Reuters' WOS is one of the databases covering comprehensive research types and timely data updates. All studies about gut microbiota and host immune response published from 2011 to 2021 were obtained from this database. The search was completed on 31 December 2021, to avoid the daily update of the database that might change the included studies. The following keywords were applied to retrieve all relevant studies: TS [(gut OR intestine OR gastrointestine OR gastro-intestine) AND (microbiota OR microbiome OR flora OR microflora OR bacteria)]AND TS [macrophage OR neutrophil OR (NK cell) OR (natural killer cell) OR (dendritic cell) OR (DC) OR (innate lymphoid cells) OR (ILCs) OR (T cell) OR (T lymphocyte) OR (B cell) OR (B lymphocyte) OR (regulatory T cell) OR (Treg) OR (monocyte) OR immunosuppression OR (immune dysfunction) OR (immune response)] AND Language = English. Only original articles were included, and those irrelevant to the topic were filtered manually. This selection was carried out by two experienced researchers (Z.-X.N. and S.W.) in the field, and disagreements were resolved by an experienced corresponding author (C.-Q.Y.). The article titles and abstracts were first analyzed, and articles that were consistent with the topic content were included based on manual analysis of their content. Full-text articles that could not be judged by the title of the article were downloaded from the Naval Medical University library and further analyzed to ensure that the article topics are relevant to our study. The detailed information on enrolment and selection is shown in Figure 1.

Flow diagram of the inclusion process. The detailed process of screening and enrolment (irrelevant articles were manually screened by two authors through abstracts and full texts, and articles irrelevant to the topic were excluded).