Polysaccharide A from Bacteroides fragilis has been shown to promote IL-10 secretion by CD4+ T cells (Zhong et al., 2024), while extracellular polysaccharides from Bifidobacterium longum inhibit Th17 responses in both the gut and lungs (Li D. et al., 2025), thereby reducing asthma susceptibility. The gene discussed is CD4; the disease is asthma.