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. Author manuscript; available in PMC: 2022 Mar 10.
Published in final edited form as: Cell Host Microbe. 2021 Mar 10;29(3):334–346. doi: 10.1016/j.chom.2021.02.009

Figure 2: Mechanisms by which SIgA affects bacteria.

Figure 2:

Mechanisms by which SIgA influence gut microbes. The current mechanisms by which SIgA can affect microbes can either be divided into ways in which SIgA causes Elimination or Neutralization of bacteria or ways in which SIgA can alter gene expression patterns or functions of microbes that might actually aid in their colonization. (A) SIgA eliminates toxins and/or neutralizes microbial molecules by direct binding. This binding prevents binding of the microbial molecule/toxin to the host target receptor so that it will eventually be cleared by peristalsis. (B) by directly binding to the pathogen and by limiting motility and likely invasion. For instance, SIgA can bind to flagella and prevent organisms from accessing the epithelia. These organisms are likely to be eliminated by peristalsis. (C) Aggregation of rapidly dividing bacteria by enchained growth prevents over-population by proliferation while also limiting access to the epithelia. These organisms are likely eliminated by peristalsis. (D) Biofilms are often mechanisms by which microbes can adhere to surfaces and allow colonization. SIgA can prevent biofilm formation which would be predicted to prevent some organisms from colonizing surfaces. It is also possible that that this mechanism could prevent the expression of genes required for biofilm formation. Therefore, this could be a mechanism for both Elimination and Sculpting. (E) SIgA can preferentially bind to surface microbial molecules that anchor the microbe to the epithelial surface. In this way, SIgA might positively select for organisms that express these molecules. (F) Microbes are known for the ability to sense environmental cues and respond by changing their gene expression patterns. SIgA binding of specific molecules on microbes might be sensed by the microbe such that binding results in down-regulation of that surface molecule. In this way, SIgA could fine-tune microbial gene expression to prevent the production of proteins that may be harmful to the host.