Mucosa-associated lymphoid tissue (MALT)

Mucosal membranes are the major sites of entry for most pathogens. Mucosa-associated lymphoid tissue (MALT) organizes the response to antigens that enter mucosal Tissues.

Lymphoid tissue associated with different mucosal areas is sometimes given more specific names; for instance, associated with the intestinal epithelium is referred to as gut-associated lymphoid tissue.

The outer mucosal layer contains intraepithelial lymphocytes, many of which are T cells. The lamina propria, which lies under the epithelial layer, contains large numbers of B cells, plasma cells, activated T cells, and macrophages in a loose cluster.

Peyer’s patches develop into secondary follicles with germinal centers, where antigen-specific B cells are activated, proliferate, differentiate, and mutate their antibody genes, resulting in the secretion of antibodies with altered sequences in their antigen-combining sites.

M cells are flattened epithelial cells, which lack the microvilli. It transports antigens across the epithelium.

Antigens in the intestinal lumen are endocytosed into vesicles that are transported from the luminal membrane to the underlying pocket membrane.

The vesicles then fuse with the pocket membrane, delivering antigens to clusters of lymphocytes and antigen-presenting cells, the most important of which are dendritic cells, contained within the pocket.

ultimately leading to the activation of B cells that differentiate and then secrete IgA.