Ag85a/b DNA vaccine therapy improves the anabolism of tuberculosis.
In the TB model group, most of the down-regulated DE genes were related to cell structural proteins and cell functional proteins, and the functional proteins of alveolar epithelial cells account for a large proportion, such as Sftpc, Sftpb, Sftpd, Sftpa1, Mgp, Wfdc2, Sec14l3, Postn, Cldn5, Aqp5, Emp2, Foxf1, etc. Surfactant protein A (SFTPA, encoded by two homologous genes Sftpa1 and Sftpa2), B (SFTPB), C (SFTPC), and D (SFTPD), secreted by alveolar epithelial cell type II, are key elements of the innate immune system to maintain normal alveolar structure and function and resist MTB infection(63, 64). Among them, SFTPB and SFTPC play a role in reducing surface tension, and SFTPC also plays an immunomodulatory role in clearing lung infection(65). SFTPA and SFTPD are host defense lectins, which participate in the innate immune response in the lung, and enhance the phagocytosis of macrophages on MTB through interaction with alveolar macrophages(66, 67), thereby enhancing microbial clearance and regulating inflammation. SFTPA and SFTPD also regulate the functions of dendritic cells and T cells(68). Sftpa, Sftpd, and Sftpc gene polymorphisms not only increase the risk of TB but also may affect the host’s immune response to MTB(69). Thacker VV et al.(70) showed that the decreased expression of alveolar epithelial cells type II markers (Abca3, Sftpa, Sftpb, Sftpc, Sftpd) and type I markers (Aqp5 and Pdpn) would lead to the rapid growth of MTB in macrophages and alveolar epithelial cells(71). The growth of MTB in these two cells could be inhibited by the exogenous addition of Curosurf (surfactant substitute of phospholipid and hydrophobic protein). Mgp, a vitamin K-dependent inhibitor of calcification, may play an anti-inflammatory role in monocytes and macrophages(72, 73). Claudin-5 (Cldn5), a tight junction protein, is mainly expressed by the vascular endothelium, especially expressed strongly in the endothelium of normal lungs(74). The expression levels of Cldn5 were significantly decreased in various lung diseases, such as Covid-19(75), chronic obstructive pulmonary disease (COPD)(76), and lung injury(77), which induced damage to the pulmonary endothelial barrier. Induction of Cldn5 expression has become a therapeutic strategy for these diseases(77). Both our study and GSE89403 found that MTB infection significantly reduced the expression of Sftpd and Cldn5, but the treatment of ag85a/b DNA vaccine and GSE89403 significantly increased the expression of Sftpd and Cldn5, proving that Sftpd and Cldn5 can also become the targets for TB treatment. Both our study and the GSE89839 showed that Mgp expression decreased after MTB infection, which may affect the anti-inflammatory effect of mice. However, after the treatment of ag85a/b DNA vaccine and GSE89403, the expression of Mgp was significantly increased, suggesting that the anti-inflammatory effect of mice may be improved. The mouse Retnla (human Retn), a member of the resistin family, is a secreted protein rich in cysteine. It is not only a protein related to insulin resistance but also a pro-inflammatory molecule(78). Retnla is a negative regulator of Th2-mediated pneumonia. Retnla-/- mice developed exacerbated lung inflammation compared with their wild-type controls(79). In this study, the expression of Retnla was significantly down-regulated in the mouse TB model, which was consistent with the results from two GSE data sets. In TB patients, Retn gene expression also showed a downward trend. The down-regulation of Retnla (Retn) expression caused Th1 immune response to shift to Th2 immune response, while the immunotherapy of theag85a/b DNA vaccine significantly increased Retnla expression, which was conducive to correcting Th1/Th2 immune imbalance(78). After the immunotherapy with ag85a/b DNA vaccine IM or EP in the mice infected with MTB, the anabolism, developmental process, and immune response-related pathways (such as ECM receiver interaction, Focal induction, PI3K Akt signaling pathway, Rap1 signaling pathway, etc.) were enhanced, the transcriptional levels of the surfactant genes were significantly up-regulated, the number of MTB colonies in the lung was reduced, and the lung lesions in mice were alleviated, which proved that pulmonary surfactants have a potential role in the host-directed treatment of TB(71). The mechanism may be that surfactants can inhibit the growth of MTB by changing the interaction between MTB and host cells(80). In addition, surfactants can remove the virulence-related proteins and lipids on the surface of MTB, and can wrap bacteria, so that they are not easy to infect host cells. Therefore, ag85a/bDNA vaccine IM or EP immunization can improve the immune response, eliminate MTB, and then correct metabolic disorders in mice.