The first example of an isoallotype of human IgG located on the Fd fragment

Human Gm, Km, and Am allotypes and their molecular characterization: a remarkable demonstration of polymorphism

Human immunoglobulin allotypes are antigenic determinants (or "markers") determined serologically, classically by hemagglutination inhibition, on the human immunoglobulin (IG) heavy and light chains. The allotypes have been identified on the gamma1, gamma2, gamma3, and alpha2 heavy chains (they are designated as G1m, G2m, G3m, and A2m allotypes, respectively), and on the kappa light chain (Km allotypes). Gm-Am allotypes are inherited in fixed combinations, or Gm-Am haplotypes, owing to the linkage of the human IGHC genes (IGHG3, IGHG1, IGHA1, IGHG2, IGHG4, IGHE, and IGHA2 from 5' to 3' in the IGH locus on chromosome 14). Gm and Am allotypes have been one of the most powerful tools in population genetics and very instrumental in molecular characterization of the human IGHC genes (gene conversion, copy number variation, gene order). They represent a major system for understanding immunogenicity of the polymorphic IG chains, in relation with amino acid and conformational changes. The correlation between G3m allotypes and amino acid changes has been possible with the sequencing of many alleles of the IGHG3 gene, from individuals from different populations and with known allotypes. In this chapter, we integrate genetics and sequence data and provide an updated overview of the Gm-Am haplotypes and Km allotypes. We propose, for the first time, a complete elucidation of the G3m allotypes, illustrated by the "IMGT G3m allele butterfly" concept that allows a graphical representation of the G3m alleles (variants of a gene expressing a given set of allotypes). Knowledge of allotypes is important in antibody engineering and humanization of monoclonal antibodies to improve immunotherapy.

Development of two murine monoclonal antibodies recognizing human nG1m(a)-like isoallotypic markers

Antigenic determinants of immunoglobulin molecules are categorized into three groups: idiotypes, isotypes, and allotypes. An isoallotype is defined as an isotypic determinant in one or more subclasses and an allotype in another subclass of a given isotype. The isoallotype nG1m(a), formerly called non-a, is an allotype located on human IgG1 molecules lacking the G1m(a) allotype. This marker, however, is also detectable on all human IgG2 and IgG3 molecules. Anti-isoallotypic antibodies are useful tools for structural studies of immunoglobulins, forensic science, and epidemiological demographic investigations. In this study, two murine monoclonal antibodies (MAbs) recognizing nG1m(a)-like epitope(s) were generated against a human IgG myeloma protein. These MAbs are produced by hybridoma clones (4F18B12 and 6F18D1) obtained by fusion of SP2/0 myeloma cells with splenocytes from BALB/c mice immunized with heavy chain of a human IgG3 myeloma protein. These MAbs reacted with Fc, but not Fab fragment of the immunizing IgG3 paraprotein. Specificity of the MAbs was further analyzed using a panel of purified myeloma proteins and polyclonal IgG3, including IgG1 (n = 9), IgG2 (n = 4), IgG3 (n = 8), and IgG4 (n = 6) subclasses. Our results demonstrated that these MAbs reacted with linear epitope(s) located on heavy chain of all IgG2 and IgG3 molecules tested and some paraproteins of IgG1 subclass, but none of the IgG4 molecules. So these MAbs seem to recognize nG1m(a)-like isoallotypic marker. These MAbs showed no cross-reactivity with serum of other species tested. Both MAbs belonged to IgG1 subclass with affinity constants of 4.5 x 10(9) mol(-1) (4F18B12) and 3.46 x 10(9) mol(-1) (6F18D1), respectively. These MAbs might be used as a tool to detect nG1m(a) + IgG molecules.

Human IgG allotypes co-occurring in more than one IgG subclass

Inheritance of an excess of immunoglobulin allotypes in one haplotype was encountered which could not be explained by the assumption of a duplicated locus. The surplus of allotypes was related to markers on the CH3 domain of gamma 3 chains. Two such cases were investigated extensively. The IgG3 molecules were isolated by gel filtration and by absorption on protein A. Only the usual combination of allotypes appeared to be present on the IgG3 molecules. The supernumerary markers were found in one case on IgG2 molecules and in the other case on IgG1 molecules. This followed from investigations of eluates after separation of the subclasses by immune absorptions. A hypothesis was proposed to explain these events by mutation of a particular position of an otherwise homologous stretch of gamma-subclass DNA.

Human IgG3 allotypes, with special reference to a new allotype related to G3m(g) (G3m21)

The IgG3 allotype described as L1 (Blanc et al., 1976) occurs on the CH3 region of G3m(g) proteins, in contrast to G3m(g) that is known to be present on the CH2 region. G3m(g) and L1 are, as a rule, present on the same gamma3 heavy chain, just like the G3m(b) subspecificities of the CH2 region, (b1) and (b4), with those of the CH3 region (b0), (b3) and (b5). Several families were investigated that showed inheritance of rare combinations of IgG3 allotypes. The data obtained are suggestive for notation of L1 as (g5), since L1 probably occupies a position antithetical to (b5). The relation of amino acid substitutions to allotypes and isoallotypes is discussed.