serum sickness A usually self-limiting immunological hypersensitivity reaction originally seen in response to the therapeutic injection of large amounts of foreign serum (now most usually evoked by the injection of drugs such as penicillin). It is caused by the formation of immune complexes of the antigen and the antibodies formed against it, which become deposited in the tissues, especially the kidneys.
severe combined immunodeficiency (SCID) Type of immune deficiency (due to various causes) in which both B-cell (antibody) and T-cell responses are lacking; it is fatal if not treated.
severe congenital neutropenia (SCN) An inherited condition in which the neutrophil count is persistently extremely low. This is in contrast to cyclic neutropenia, in which neutrophil numbers ﬂuctuate from near normal to very low or absent, with an approximate cycle time of 21 days.
SH2 (Src homology 2) domain See Src-family protein tyrosine kinases.
shear-resistant rolling The capacity of neutrophils to maintain attached to the vascular endothelium under high rates of ﬂow—or shear—enabled by specialized plasma membrane extensions called slings.
shingles Disease caused when herpes zoster virus (the virus that causes chickenpox) is reactivated later in life in a person who has had chickenpox.
SHIP (SH2-containing inositol phosphatase) An SH2-containing inositol phosphatase that removes the phosphate from PIP3 to produce PIP2.
shock The potentially fatal circulatory collapse caused by the systemic actions of cytokines such as TNF-α.
SHP (SH2-containing phosphatase) An SH2-containing protein phosphatase.
signal joint The noncoding joint formed in DNA by the recombination of RSSs during V(D)J recombination. Cf. coding joint.
signal peptide The short N-terminal peptide sequence responsible for directing newly synthesized proteins into the secretory pathway.
signal transducers and activators of transcription (STATs) See Janus kinase (JAK) family.
signaling scaffold A configuration of proteins and modifications, such as phosphorylation or ubiquitination, that facilitates signaling by binding various enzymes and their substrates.
single-chain antibody Referring to the heavy-chain-only IgGs produced by camelids or shark species that lack the light chain present in conventional antibodies.
single-nucleotide polymorphisms (SNPs) Positions in the genome that differ by a single base between individuals.
single-positive thymocytes A mature T cell that expresses either the CD4 or the CD8 co-receptor, but not both.
single-stranded RNA (ssRNA) Normally confined to the nucleus and cytoplasm, this normal molecular form serves as a ligand for TLR-7, TLR-8, and TLR-9 when it is present in endosomes, as during parts of a viral life cycle.
sipuleucel-T (Provenge) Cell-based immunotherapy used to treat prostate cancer that combined prostatic acid phosphatase as a tumor rejection antigen presented by dendritic cells derived from a patient's monocytes.
sirolimus See rapamycin.
Sjögren’s syndrome An autoimmune disease in which exocrine glands, particularly the lacrimal glands of the eyes and salivary glands of the mouth, are damaged by the immune system. This results in dry eyes and mouth.
Skint-1 A transmembrane immunoglobulin superfamily member expressed by thymic stromal cells and keratinocytes that is required for the development of dendritic epidermal T cells, which are a type of γ:δ T cell.
SLAM (signaling lymphocyte activation molecule) A family of related cell-surface receptors that mediate adhesion between lymphocytes, that includes SLAM, 2B4, CD84, Ly106, Ly9, and CRACC.
slings See shear-resistant rolling.