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The delivery mechanism of oral vaccines serves to protect the antigen from the low-pH environment and digestive tract proteases, as well as to effectively transport the active components of the vaccine to the small intestine. The antigen is taken up by antigen-presenting cells, such as dendritic cells (DCs), which present the antigens to T cells in the gut-associated lymphoid tissue (GALT), thereby inducing mucosal humoral immunity and cellular immune responses. DCs migrate to the mesenteric lymph node and promote the activation of antigen-specific T and B lymphocytes.
Following activation, lymphocytes undergo proliferation and differentiation, and these activated clonal lymphocytes exit the mesenteric lymph node and enter the bloodstream. DCs play a key role in regulating the expression of homing molecules on the surface of activated lymphocytes.
Once in circulation, most activated lymphocytes return to the site where the antigen was initially encountered. However, a portion of these lymphocytes also migrates to distant mucosal tissues, beyond the site where the antigen was taken up. This activation of antigen at a mucosal inductive site that leads to effector and/or memory T and B cells in distant mucosal sites forms the basis of the common mucosal immune system.
For this reason, antigens administered orally can also induce immune responses in respiratory mucosa, as discussed in our next article, which will be published on pig333.com on 15 Setember 2025 "Oral vaccines against respiratory diseases: activating the common mucosal immune system".
