Mucosa-associated lymphoid tissue (MALT)
Mucosa-associated lymphoid tissue comprises lymphoid follicles in mucosal linings that defend against pathogens.
Mucosa-associated lymphoid tissue (MALT) is a diffuse collection of non-encapsulated lymphoid tissue found throughout mucosal surfaces of the body. It plays a critical role in the immune surveillance and defense of mucosal membranes — which are common entry points for pathogens. MALT includes organized structures like Peyer’s patches as well as scattered immune cells embedded in mucosa.
Distribution
MALT is widely distributed in the following systems:
- Gastrointestinal tract: Most abundant (gut-associated lymphoid tissue, GALT)
- Respiratory tract: (bronchus-associated lymphoid tissue, BALT)
- Urogenital tract
- Oropharynx: Including tonsils
- Conjunctiva: Eye-associated lymphoid tissue (CALT)
Types of MALT
Type | Location | Examples |
---|---|---|
GALT (Gut-associated lymphoid tissue) | Intestinal mucosa | Peyer’s patches, appendix, isolated lymphoid follicles |
BALT (Bronchus-associated lymphoid tissue) | Bronchial walls and lungs | Subepithelial lymphoid clusters in bronchioles |
CALT (Conjunctival-associated lymphoid tissue) | Eye conjunctiva | Lymphoid follicles along the inner eyelid |
SALT (Skin-associated lymphoid tissue) | Dermis and epidermis | Langerhans cells, dermal dendritic cells |
Structure
- May be diffuse (scattered lymphocytes) or organized (e.g., Peyer’s patches)
- Composed of:
- Lymphoid follicles (B cells)
- Interfollicular T cells
- Antigen-presenting cells (dendritic cells, macrophages)
- M cells (microfold cells) in intestinal epithelium that transport antigens to underlying lymphoid tissue
Function
- Immune Surveillance: Constantly monitors and responds to antigens at mucosal surfaces
- Antigen Sampling: M cells capture antigens and deliver them to lymphoid cells beneath the epithelium
- IgA Production: Stimulates plasma cells to secrete IgA, which neutralizes pathogens at mucosal surfaces
- Memory Cell Generation: Develops long-lasting mucosal immune memory
Blood and Lymphatic Supply
- Supplied by local mucosal capillaries and arterioles
- Drains into nearby lymphatic vessels and regional lymph nodes
Clinical Significance
- Appendicitis: Inflammation of the appendix (a GALT-rich structure)
- Peyer’s patches infection: Entry site for pathogens like Salmonella or poliovirus
- MALT lymphoma: A type of extranodal non-Hodgkin lymphoma; commonly arises in stomach, often associated with chronic H. pylori infection
- Autoimmunity and chronic inflammation: Excess MALT activity may contribute to diseases like IBD or Sjögren’s syndrome
Comparative Anatomy
MALT is present in many vertebrates. In mammals, particularly humans, it has evolved to provide strong mucosal immunity due to high antigen exposure from the environment, diet, and airborne particles.
Last updated on May 12, 2025