Rheb A small GTPase that activates mTOR when in its GTP-bound form, and is inactivated by a GTPase-activating protein (GAP) complex TSC1/2.
rheumatic fever Disease caused by antibodies elicited by infection with some Streptococcus species. These antibodies cross-react with kidney, joint, and heart antigens.
rheumatoid arthritis (RA) A common inﬂammatory joint disease that is probably due to an autoimmune response.
rheumatoid factor An anti-IgG antibody of the IgM class first identified in patients with rheumatoid arthritis, but which is also found in healthy individuals.
Rho See Rho family small GTPase proteins.
Rho family small GTPase proteins Several distinct small GTPase family members that regulate the actin cytoskeleton in response to signaling through various receptors. Examples: Rac, Rho, and Cdc42.
Rictor See mTORC2.
RIG-I (retinoic acid-inducible gene I) See RIG-I-like receptors (RLRs).
RIG-I-like receptors (RLRs) A small family of intracellular viral sensors that use a carboxy terminal RNA helicase-like domain in detection of various forms of viral RNA. These signal through MAVS to activate antiviral immunity. Examples include RIG-I, MDA-5, and LGP2.
RIP2 A CARD domain containing serine-threonine kinase that functions in signaling by NOD proteins to activate the NFκB transcription factor.
Riplet An E3 ubiquitin ligase involved in signaling by RIG-I and MDA-5 for the activation of MAVS.
rituximab A chimeric antibody to CD20 used to eliminate B cells in treatment of non-Hodgkin's lymphoma.
R-loops A structure formed when transcribed RNA displaces the nontemplate strand of the DNA double helix at switch regions in the immunoglobulin constant-region gene cluster. R-loops are thought to promote class switch recombination.
RNA exosome A multisubunit complex involved in processing and editing of RNA.
ruxolitinib An inhibitor of JAK1 and JAK2 approved for treatment of myelofibrosis.
S1PR1 A G protein-coupled receptor expressed on circulating lymphocytes that binds the chemotactic phospholipid, sphingosine 1-phosphate, which forms a chemotactic gradient that promotes the egress of non-activated lymphocytes out of secondary lymphoid tissues into the efferent lymphatics and blood. See also CD69.
SAP (SLAM-associated protein) An intracellular adaptor protein involved in signaling by SLAM (signaling lymphocyte activation molecule). Inactivating mutations in this gene cause X-linked lymphoproliferative (XLP) syndrome.
scaffolds Adaptor-type proteins with multiple binding sites, which bring together specific proteins into a functional signaling complex.
scavenger receptors Receptors on macrophages and other cells that bind to numerous ligands, such as bacterial cell-wall components, and remove them from the blood. The Kupffer cells in the liver are particularly rich in scavenger receptors. Includes SR-A I, SR-A II, and MARCO.
scid   Mutation in mice that causes severe combined immunodeficiency. It was eventually found to be due to mutation of the DNA repair protein DNA-PK.
SCID See severe combined immunodeficiency.
seasonal allergic rhinoconjunctivitis IgE-mediated allergic rhinitis and conjunctivitis caused by exposure to specific seasonally occurring antigens, for example grass or weed pollens. Commonly called hay fever.