Nasal-associated lymphoid tissue
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Nasal- or nasopharynx- associated lymphoid tissue (NALT) represents immune system of nasal mucosa and is a part of mucosa-associated lymphoid tissue (MALT) in mammals.[1] It protects body from airborne viruses and other infectious agents. In humans, NALT is considered analogous to Waldeyer's ring.[2]
NALT in mice is localized on cartilaginous soft palate of upper jaw, it is situated bilaterally on the posterior side of the palate. It consists mainly of lymphocytes, T cell and B cell enriched zones, follicle-associated epithelium (FAE) with epithelial M cells and some erythrocytes. M cells are typical for antigen intake from mucosa. In some areas of NALT, there are lymphatic vessels and HEVs (high endothelial venule). Dendritic cells and macrophages are also present.
NALT contains about same amount of T cells and B cells. The T-cell population contains about 3–4 times more CD4+ T cells than CD8+ T cells. Most of T cells are with αβ T cell receptor (TCR) and only few are with γδ TCR. CD4+ T cells are in naive state, marked by high expression of CD45RB. B cells are mostly in unswitched state, with sIgM+ IgD+ phenotype.[3][4]
Development
Formation of NALT starts early after birth, it is not present during embrygenesis or in newborn mice. First signs of NALT (HEV with associated lymphocytes) occurs one week after birth, but full formation is established after 5–8 weeks. In contrast to Peyer's patches and lymph nodes, NALT formation is independent of IL-7R, LT-βR and ROR-γ signalling. It requires Id2 gene, which induce genesis of CD3−CD4+CD45+ cells. These cells accumulates on the site of NALT after birth and induce NALT formation.[4]