n. a molecule that binds to another molecule, as in antigen–antibody and hormone–receptor bondings.
n. any one of a family of proteins that form the protein components of *lipoproteins, which transport hydrophobic lipid molecules in the plasma. Individual members of the family are designated by the abbreviation ‘Apo’ followed by a capital letter. Apolipoproteins have a range of molecular weights and perform a variety of functions during the life cycle of the lipoproteins in which they are found. These include acting as ligands for the binding of enzymes (ApoB) and as cofactors for the action of other enzymes (ApoA and ApoC).... apolipoprotein
an inherited immunodeficiency syndrome characterized by normal or high IgM levels with absence of IgA, IgG, and IgE (see immunoglobulin). Patients are susceptible to bacterial and opportunistic infections. Some cases are due to a mutation in the gene encoding the CD40 ligand, which is synthesized by *helper T cells and is involved in activation of B cells to produce circulating antibodies.... hyper-igm syndrome
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