mitogen-activated protein kinases (MAPKs) A series of protein kinases that become phosphorylated and activated on cellular stimulation by a variety of ligands, and lead to new gene expression by phosphorylating key transcription factors. The MAPKs are part of many signaling pathways, especially those leading to cell proliferation, and have different names in different organisms.
mixed essential cryoglobulinemia Disease due to the production of cryoglobulins (cold-precipitable immunoglobulins), sometimes in response to chronic infections such as hepatitis C, which can lead to the deposition of immune complexes in joints and tissues.
mixed lymphocyte reaction (MLR) A test for histocompatibility in which lymphocytes from donor and recipient are cultured together. If the two people are histoincompatible, the recipient’s T cells recognize the allogeneic MHC molecules on the cells of the other donor as ‘foreign’ and proliferate.
molecular mimicry The similarity between some pathogen antigens and host antigens, such that antibodies and T cells produced against the former also react against host tissues. This similarity may be the cause of some autoimmunity.
monoclonal antibodies Antibodies produced by a single clone of B lymphocytes, so that they are all identical.
monocyte Type of white blood cell with a bean-shaped nucleus; it is a precursor of tissue macrophages.
monomorphic Describes a gene that occurs in only one form. Cf. polymorphic.
motheaten A mutation in the SHP-1 protein phosphatase that impairs the function of some inhibitory receptors, such as Ly49, resulting in over-activation of various cells, including NK cells. Mice with this mutation have a 'motheaten' appearance due to chronic inﬂammation.
MR1 A 'non-classical' MHC class Ib molecule that binds certain folic acid metabolites produced by bacteria for recognition by mucosal associated invariant T (MAIT) cells.
MRE11A (meitotic recombination 11 homolog a) A protein involved in DNA damage and repair mechanisms that also recognizes cytoplasmic dsDNA and can activate the STING pathway.
MSH2, MSH6 Mismatch repair proteins that detect uridine and recruit nucleases to remove the damaged and several adjacent nucleotides.
mTOR (mammalian target of rapamycin) Serine/threonine kinase that functions in regulating numerous aspects of cell metabolism and function in complex with regulatory proteins Raptor or Rictor. The Raptor/mTOR complex (mTORC1) is inhibited by the immunosuppressive drug rapamycin.
mTORC1, mTORC2 Active complexes of mTOR formed with the regulatory proteins Raptor and Rictor, respectively.
mucins   Highly glycosylated cell-surface proteins. Mucin-like molecules are bound by L-selectin in lymphocyte homing.
Muckle–Wells syndrome An inherited episodic autoinﬂammatory disease caused by mutations in the gene encoding NLRP3, a component of the inﬂammasome.
mucosal associated invariant T cells (MAIT) Primarily γ:δT cells with limited diversity present in the mucosal immune system that respond to bacterially derived folate derivates presented by the nonclassical MHC class Ib molecule MR1.
mucosa-associated lymphoid tissue (MALT) Generic term for all organized lymphoid tissue found at mucosal surfaces, in which an adaptive immune response can be initiated. It comprises GALT, NALT, and BALT (when present).
mucosal epithelia   Mucus-coated epithelia lining the body’s internal cavities that connect with the outside (such as the gut, airways, and vaginal tract).