Much of our immune defense against invading organisms is predicated upon the tremendous diversity of immunoglobulin (Ig) molecules. Igs are glycoproteins produced by B lymphocytes and plasma cells. These molecules can be considered receptors because the primary function of the Ig molecule is to bind antigen. A single person can synthesize 10–100 million different Ig molecules, each having a distinct antigen-binding specificity. The great diversity in this so-called humoral immune system allows us to generate antibodies specific for a variety of substances, including synthetic molecules not naturally present in our environment. Despite the diversity in the specificities of antibody molecules, the binding of antibody to antigen initiates a limited series of biologically important effector functions, such as complement activation or adherence of the immune complex to receptors on leukocytes. The eventual outcome is the clearance and degradation of the foreign substance. This chapter describes the structure of Igs and outlines the mechanisms by which B cells produce molecules of such tremendous diversity with defined effector functions.
Acronyms and Abbreviations
ADCC, antibody-dependent cellular cytotoxicity; AID, activation-induced deaminase; APRIL, a proliferation inducing ligand; BACH2, basic leucine zipper transcription factor 2; BAFF B-cell activating factor; BCL-6, B-cell chronic lymphocytic leukemia/lymphoma 6; BiP, immunoglobulin-binding protein; Blimp-1, B-lymphocyte-induced maturation protein-1; BLNK, B-cell linker protein; BTK, Bruton tyrosine kinase; C, constant; CDR, complementarity determining region; CRI, cross-reactive idiotype; CSR, class switch recombination; D, diversity; DLBCL, diffuse large B-cell lymphoma; DNA-PK, DNA protein kinase; DSB, double strand break; E5, exon 5; E2F1, E2F transcription factor 1; EBF1, early B-cell factor 1; ER, endoplasmic reticulum; ERGIC, ER-Golgi-intermediate compartment; FCRL4, Fc receptor like protein 4; FR, framework region; H, heavy; HMG, high-mobility group protein; HR, homologous repair; HS1, hepersensitive site 1; Ig, immunoglobulin; IL, interleukin; IRF4, interferon regulatory factor 4; IRTA1, immunoglobulin superfamily receptor translocation-associated 1; ITAM, immunoreceptor tyrosine-based activation motif; κ, immunoglobulin kappa light chain; Kde, kappa-deleting element; λ, immunoglobulin lambda light chain; L, light; Lig 4, DNA ligase IV; MITF, microphthalmia-associated transcription factor; MYBL1 and 2, v-myb myeloblastosis viral oncogene homologues 1 and 2; NHEJ, nonhomologous DNA end-joining; PAX5, paired box gene 5; PDI, protein disulphide isomerase; PLC, phospholipase C; POU2AF1, Pou domain, class 2, associating factor 1; POU2F2, Pou domain, class 2, factor 2; PRDM1, positive regulatory domain 1-binding factor-1; RAG, recombination-activating gene; RSS, recombination signal sequence; SCID, severe combined immunodeficiency; SH2, scr homology 2; SHP-1, Src homology 2 domain-containing protein tyrosine phosphatase-1; SHIP-1, phosphatidylinositol-3,4,5-trisphosphate 5-phosphatase 1; TCFE2A, transcription factor E2a; UNG, uracil-DNA glycosylase; V, variable-region gene; V(D)J, exon created by a rearranged immunoglobulin heavy-chain variable-region gene, diversity gene segment, and joining gene segment; XBP1, X-box binding protein-1; XRCC4, X-ray repair complementing defective repair in chinese hamster ovary cells protein-4.
All naturally occurring immunoglobulin (Ig) molecules are composed of one or several basic units consisting of two identical heavy (H) chains ...