Patients with chronic obstructive pulmonary disease (COPD) are 2-3 times more likely to occur together with chronic gastrointestinal tract (GIT) diseases, such as inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS). Similarly, despite many patients have no history of acute or chronic respiratory disease, up to 50% of IBD patients and 33% of IBS patients have pulmonary involvement, such as inflammation or impaired lung function. Increasing evidence indicated chronic gut and lung disease share key conceptual features with the disorder and dysregulation of the microbial ecosystem. However, the underlying mechanisms are not well understood.

Our study is aimed to elucidate the intimate relationship between the gastrointestinal tract and respiratory tract, and uncover the mechanisms by which the gut microbiota affects the immune responses in the lungs, and vice versa.

Inclusion Criteria:

• admitted to hospital with an exacerbation of COPD;
• with no history of probiotics taken;
• the duration of antibiotics treatment before enrollment should be less than 72 hours.

Exclusion Criteria:

• being immunocompromised, including history of glucocorticoid taken for more than 1 month, history of immunosuppressive therapy, history of human immunodeficiency virus (HIV) infection, solid tumor or hematological malignancy;
• history of long-term nursing home stays;
• history of recently hospitalized (<90 days).

Patients admitted to Peking University People's Hospital and Ningde City Hospital with an exacerbation of COPD between January 2017 and January 2019 will be enrolled.