TNF and chronic obstructive pulmonary disease: Subgroup analyses demonstrated that probiotics significantly reduced TNF-α levels in CS-induced COPD animals (SMD = -4.08, 95% CI: -5.26 to -2.90, z = -6.789, p = 0.000 < 0.05), as well as in DEP-induced COPD animals (SMD = -1.71, 95% CI: -2.66 to -0.76, z = -3.542, p = 0.000 < 0.05).