Subject – immunology Topic – Local immunity .

Lymphoid tissue associated with mucous membranes, lungs, skin

LOCAL IMMUNITY •

Astate of protection against disease in a particular organ, tissue, or anatomical site, mediated by localized antibodies or lymphoid cells.

Lymphoid Tissue

Mucosal surfaces have one challenge that is not present in other areas of the body. For a moment, take the point of view of a pathogen.

Lymphoid tissue associated with mucous membrane

• The mucosa-associated lymphoid tissue (MALT), also called mucosa-associated lymphatic tissue, is a diffuse system of small concentrations of lymphoid tissue found in various sub-mucosa membrane sites of the body, such as the gastrointestinal tract, thyroid, breast, lung, salivary glands, eye, and skin.

• MALT is populated by lymphocytes such as T cells and B cells, as well as plasma cells and macrophages, each of which is well situated to encounter antigens passing through the mucosal epithelium.

• In the case of intestinal MALT, M cells are also present, which sample antigen from the lumen and deliver it to the lymphoid tissue.

• Chronic inflammation of MALT from infective or autoimmune disorders can lead to the development of extra nodal marginal zone B-cell lymphomas, or MALTomas. The stomach is the most common location of MALTomas, while frequent nongastric sites include the following :

• Salivary glands• Skin• Orbits and conjunctiva• Lung• Thyroid• Upper airways• Breast• Other gastrointestinal (GI) sites• Liver• MALTomas at different sites may involve different genetic lesions and may

possibly have different natural histories. [4]

• Symptoms of MALTomas are nonspecific and are related to the organs involved. Most patients with MALTomas have no physical findings; lymphadenopathy is rare.

Mucous membrane associated with lungs

• Bronchus-associated lymphoid tissue (BALT) is a constitutive mucosal lymphoid tissue adjacent to major airways in some mammalian species, including rats and rabbits, but not humans or mice.

• A related tissue, inducible BALT , is an ectopic lymphoid tissue that is formed upon inflammation or infection in both mice and humans and can be found throughout the lung. Both BALT and iBALT acquire antigens from the airways and initiate local immune responses and maintain memory cells in the lungs.

• The development and function of BALT and iBALT in the context of pulmonary immunity to infectious agents, tumors, and allergens as well as autoimmunity and inflammatory diseases of the lung.

Skin associated lymphoid tissue • Skin is subjected to physicochemical stresses such as irradiation with

ultraviolet light that alter dramatically its immunologic properties. Skin with lymphoid cells, reticular cells .

• Evidence in favour of the existence of skin-associated lymphoid tissues (SALT) includes

• (1) the cutaneous microenvironment is capable on its own of accepting, processing, and presenting nominal antigen;

• (2) strategically located peripheral lymph nodes are able to accept immunogenic signals derived from skin;

• (3) subsets of T lymphocytes display differential affinity for skin and its associated peripheral nodes; and

• (4) acquisition of this affinity by T cells is determined at least in part by differentiation signals received in situ from resident cutaneous cells.