Mucosal Vaccine Development Based on Liposome Technology

Figure 1

Principles for induction of mucosal immune responses after intranasal vaccination. The respiratory mucosal immune system consists of clusters of lymphoid cells beneath the mucosal epithelium, hosting both innate and adaptive immune cells [29]. There is a clear distinction between inductive and effector sites and these are also physically separated. Inductive sites are organized lymphoid tissues where antigen is taken up by DCs and other APCs. The effector sites, on the other hand, are tissues that provide protection against infection where specific antibodies and CD4⁺ and CD8⁺ effector and memory T cells reside [30]. The main inductive sites for mucosal immune responses after intranasal vaccination are known as nasopharynx-associated lymphoid tissue (NALT), which harbors B cell follicles and T cell zones in well demarked microanatomical areas [31]. Antigens are taken up by DCs that get access to the luminal content either through direct uptake through the epithelium or via the follicle associated epithelium (FAE) that overlay the NALT. After antigen uptake, the immature DCs undergo maturation and subsequently leave the mucosal tissue for the draining lymph nodes, alternatively, if already in the NALT, the DCs will directly prime naive CD4⁺ or CD8⁺ T cells. Activated CD4⁺ T cells differentiate into various subsets: T helper 1 (Th1), Th2, or Th17 cells, regulatory T cells (Tregs), or follicular helper T cells (). The latter are critically needed for the expansion and differentiation of the activated B cells in the germinal center (GC), which is formed in the B cell follicle in the lymph node after vaccination. cells are involved in the development of long-lived plasma cells and memory B cells in the GC.