conjugate vaccines Antibacterial vaccines made from bacterial capsular polysaccharides bound to proteins of known immunogenicity, such as tetanus toxoid.
constant Ig domains (C domains) Type of protein domain that makes up the constant regions of each chain of an immunoglobulin molecule.
constant region, C region That part of an immunoglobulin or a T-cell receptor that is relatively constant in amino acid sequence between different molecules. Also known as the Fc region in antibodies. The constant region of an antibody determines its particular effector function. Cf. variable region.
continuous epitope, linear epitope Antigenic structure (epitope) in a protein that is formed by a single small region of amino acid sequence. Antibodies that bind continuous epitopes can bind to the denatured protein. The epitopes detected by T cells are continuous. Also called a linear epitope.
conventional (or classical) dendritic cells (cDCs) The lineage of dendritic cells that mainly participates in antigen presentation to, and activation of, naive T cells. Cf. plasmacytoid dendritic cells.
co-receptors Cell-surface protein that increases the sensitivity of a receptor to its ligand by binding to associated ligands and participating in signaling. The antigen receptors on T cells and B cells act in conjunction with co-receptors, which are either CD4 or CD8 on T cells, and a co-receptor complex of three proteins, one of which is the complement receptor CR2, on B cells.
cortex The outer part of a tissue or organ; in lymph nodes it refers to the follicles, which are mainly populated by B cells.
corticosteroids Family of drugs related to natural steroids such as cortisone. Corticosteroids can kill lymphocytes, especially developing thymocytes, inducing apoptotic cell death. They are medically useful anti-inﬂammatory and immunosuppressive agents.
co-stimulatory molecules Cell-surface proteins on antigen-presenting cells that deliver co-stimulatory signals to naive T cells. Examples are the B7 molecules on dendritic cells, which are ligands for CD28 on naive T cells.
co-stimulatory receptors Cell-surface receptors on naive lymphocytes through which the cells receive signals additional to those received through the antigen receptor, and which are necessary for the full activation of the lymphocyte. Examples are CD30 and CD40 on B cells, and CD27 and CD28 on T cells.
CR1 (CD35) A receptor expressed by phagocytic cells that binds to C3b. It stimulates phagocytosis and inhibits C3 convertase formation on host-cell surfaces.
CR2 (CD21) Complement receptor that is part of the B-cell co-receptor complex. It binds to antigens coated with breakdown products of C3b, especially C3dg, and, by cross-linking the B-cell receptor, enhances sensitivity to antigen at least 100-fold. It is also the receptor used by the Epstein–Barr virus to infect B cells.
CR3 (CD11b:CD18)   Complement receptor 3. A β2 integrin that acts both as an adhesion molecule and as a complement receptor. CR3 on phagocytes binds iC3b, a breakdown product of C3b on pathogen surfaces, and stimulates phagocytosis.
CR4 (CD11c:CD18) A β2 integrin that acts both as an adhesion molecule and as a complement receptor. CR4 on phagocytes binds iC3b, a breakdown product of C3b on pathogen surfaces, and stimulates phagocytosis.
CRAC channel Channels in the lymphocyte plasma membrane that open to let calcium ﬂow into the cell during the response of the cell to antigen. Channel opening is induced by release of calcium from the endoplasmic reticulum.