Nomenclature of MALT

1. RECOMMENDED NOMENCLATURE FOR MUCOSAASSOCIATED IMMUNE-CELL COMPARTMENTS

1.1. LP Lamina propria

1.1.1. Refers usually to the connective tissue of gut mucosa, restricted to the stroma above the muscularismucosae.

1.2. IEL compartment Surface epithelium

1.2.1. Refers usually to the epithelium of the small intestine where most intraepithelial lymphocytes (IELs) occur.

1.3. FAE Follicle-associated epithelium

1.3.1. Covers the domes of MALT structures and contains variable numbers of M cells

1.4. MALT Mucosa-associated lymphoid tissue

1.4.1. The principal inductive sites for mucosal immune responses, subdivided according to anatomical location as below.

1.5. GALT Gut-associated lymphoid tissue

1.6. PP Peyer’s patch

1.7. ILF Isolated (solitary) lymphoid follicle

1.7.1. PPs and ILFs constitute the major part of GALT, but also the appendix is included although functionally less explored.

1.8. NALT Nasopharynx (or nose)-associated lymphoid tissue

1.8.1. In humans, NALT consists of the lymphoid tissue of Waldeyer’s pharyngeal ring, including the adenoids and the paired palatine tonsils.

1.9. BALT Bronchus-associated lymphoid tissue

1.10. MLN Mesenteric lymph node

1.11. CLN Cervical lymph node

2. GALT

2.1. Gut-associated lymphoid tissue (GALT) comprises PPs, the appendix, and isolated lymphoid follicles (ILFs), which are considered inductive sites for mucosal B and T cells.

2.2. Human PPs occur mainly in the distal ileum and contain by definition between 5 and 200 aggregated lymphoid follicles

2.3. The number of macroscopically identifiable human PPs increases from some 50 at the beginning of the last trimester to 100 at birth and 250 in the midteens, then diminishes to become approximately 100 between 70 and 95 years of age.

2.4. The human gut harbors at least 30,000 ILFs, increasing in density distally

3. RECOMMENDED NOMENCLATURE FOR SECRETORY IMMUNE-FUNCTION MOLECULES

3.1. SIgA (or S-IgA)

3.1.1. Secretory IgA

3.2. SIgM (or S-IgM

3.2.1. Secretory IgM

3.3. pIgA

3.3.1. Polymeric IgA

3.3.1.1. Refers mainly to dimers but also includes larger polymers of Jchain-containing IgA

3.4. J chain

3.4.1. Joining chain

3.5. SC

3.5.1. Secretory component

3.5.1.1. Exists in three forms: membrane SC; bound SC; and free SC

3.6. pIgR

3.6.1. Polymeric Ig receptor

4. MALT

4.1. The term MALT was first coined to emphasize that solitary organized mucosa-associated B-cell follicles and larger lymphoid aggregates have common features and are the origin of cells that traffic to mucosal effector sites.

4.2. MALT is sub-divided according to anatomical regions, and the distribution and composition of such lymphoid structures vary considerably with species

4.3. Age and tissue state have an impact on the appearance of MALT

4.4. Peyer ’ s patches (PPs) are typical MALT structures believed to be a main source of conventional (B2) surface (s)IgA-expressing primed (memory / effector) and class-switched mucosal B cells.

5. Inductive and Effector tissues

5.1. Inductive sites — where antigens sampled from mucosal surfaces stimulate cognate naive T and B lymphocytes

5.2. Effector Sites — where the effector cells after extravasation, retention, and differentiation perform their action, for instance by contributing to the formation of SIgA antibodies