Lee et al. (2018) found that Lactobacillus is involved in maintaining the integrity of the intestinal mucosal barrier. It reduces microbial translocation, has a role in reducing systemic immune activation, and its abundance is positively correlated with CD4+ T cell count. Another study confirmed that Bacteroides has LPS or LOS molecules capable of signaling through TLR4 to induce IFN-β to initiate antiviral responses and resistance to viral infection (Stefan et al., 2020). Here, CD4 is linked to viral infectious disease.