lytic phase, productive phase The phase of the viral life cycle in which there is active viral replication followed by destruction of the infected host cell as the virus escapes to infect new target cells.
M1 macrophages The name sometimes given to ‘classically’ activated macrophages, which develop in the context of type 1 responses and have pro-inﬂammatory properties.
M2 macrophages The name sometimes given to ‘alternatively’ activated macrophages, which develop in in the context of type 2 responses (e.g., parasite infection) and promote tissue remodeling and repair.
macroautophagy The engulfment by a cell of large quantities of its own cytoplasm, which is then delivered to the lysosomes for degradation.
macrophages Large mononuclear phagocytic cells present in most tissues that have many functions, such as scavenger cells, pathogen-recognition cells, production of pro-inﬂammatory cytokines. Macrophages arise both embryonically and from bone marrow precursors throughout life.
macropinocytosis A process in which large amounts of extracellular ﬂuid are taken up into an intracellular vesicle. This is one way in which dendritic cells can take up a wide variety of antigens from their surroundings.
MAdCAM-1   Mucosal cell-adhesion molecule-1. A mucosal addressin that is recognized by the lymphocyte surface proteins L-selectin and VLA-4, enabling the specific homing of lymphocytes to mucosal tissues.
MAIT cells See mucosal associated invariant T cells.
major basic protein Protein released by activated eosinophils that acts on mast cells and basophils to cause their degranulation.
major histocompatibility complex (MHC) A cluster of genes on human chromosome 6 that encodes a set of membrane glycoproteins called the MHC molecules. The MHC also encodes proteins involved in antigen processing and other aspects of host defense. The genes for the MHC molecules are the most polymorphic in the human genome, having large numbers of alleles at the various loci.
MAL An adaptor protein that associates with MyD88 in signaling by TLR-2/1, TLR-2/6, and TLR-4.
mannose-binding lectin (MBL) Mannose-binding protein present in the blood. It can opsonize pathogens bearing mannose on their surfaces and can activate the complement system via the lectin pathway, an important part of innate immunity.
mannose receptor (MR) A receptor on macrophages that is specific for mannose-containing carbohydrates that occur on the surfaces of pathogens but not on host cells.
mantle zone A rim of B lymphocytes that surrounds lymphoid follicles.
Mantoux test A screening test for tuberculosis in which a sterile-filtered glycerol extract of Mycobacterium tuberculosis bacilli (Tb) is injected intradermally and the result is read 48–72 hours later. Induration, firm swelling caused by infiltration into the skin of inﬂammatory cells, can indicate previous exposure to Tb, either prior vaccination or current infection of M. tuberculosis. Generally, induration at the site of injection greater than 10 mm in diameter indicates the need for additional tests to assess whether infection with Tb is present.
MAP kinase (MAPK) See mitogen-activated protein kinase.
MARCO (macrophage receptor with a collagenous structure) See scavenger receptor).
marginal sinus A blood-filled vascular network that branches from the central arteriole and demarcates each area of white pulp in the spleen.
marginal zone Area of lymphoid tissue lying at the border of the white pulp in the spleen.
marginal zone B cells A unique population of B cells found in the spleen marginal zones; they do not circulate and are distinguished from conventional B cells by a distinct set of surface proteins.