The genetic control of gamma-globulin heavy chains. Studies of the major heavy chain subgroup utilizing multiple genetic markers

Novel approach to monitor intravenous immunoglobulin pharmacokinetics in humans using polymorphic determinants in IgG1 constant domains

Clinical efficacy of intravenous immunoglobulin treatment (IVIg) is related to its pharmacokinetic (PK) profile. Its usual evaluation, by measuring serum total IgG levels, is imprecise, because IVIg cannot be distinguished from endogenous IgG. We developed ELISAs to specifically monitor the PK of IVIg using the polymorphic determinants G1m(a), G1m(x), and G1m(f). The specificity of the IgG1 allotype assays was sufficient to determine IVIg concentrations as low as 0.1 mg/mL in sera from individuals not expressing the respective markers. IVIg was quantified in posttreatment serum from patients with Guillain-Barré syndrome (GBS) by measuring IgG1 allotypes not expressed endogenously. After serotyping, 27/28 GBS patients were found eligible for IVIg monitoring using one or two genetic markers. In 17 cases, IVIg levels could be determined by both anti-G1m(a) and anti-G1m(x) measurement, showing significant correlation. Longitudinal monitoring of IVIg PK in seven GBS patients showed potential differences in clearance of total IgG versus IVIg-derived IgG, highlighting that total IgG measurements may not accurately reflect IVIg PK. To summarize, anti-IgG1 allotype assays can discriminate between endogenous IgG and therapeutic polyclonal IgG. These assays will be an important tool to better understand the variability in IVIg PK and treatment response of all patients treated with IVIg.

FURTHER STUDIES ON THE gammaG-HEAVY CHAIN GENE COMPLEXES, WITH PARTICULAR REFERENCE TO THE GENETIC MARKERS Gm(g) AND Gm(n)

The recently described Gm (g) and Gm (n) genetic markers of the γG3- and γG2-subgroups of γ-globulin were characterized in detail primarily through studies of myeloma proteins, their polypeptide chains and fragments. Antisera derived from rabbits, non-human primates and rheumatoid arthritis patients gave identical results. This contrasted with the Gm (b) system where the rabbit antisera react with a different genetic determinant (b⁰) than the sera from rheumatoid arthritis patients (b). The Gm (g) and Gm (n) antigens were detected both by precipitin analysis and by hemagglutination inhibition. The Gm (g) antigen was not associated with any of the other genetic antigens of the γG3-proteins which all belonged in the Gm (b) class. The genes for the latter were always allelic to the gene coding for Gm (g), with that for Gm (b⁰) constantly present when that for Gm (g) was absent. The Gm (g) and Gm (n) markers were of particular value in tracing the various gene complexes made up of the closely linked subgroup genes. Further support was gained for the concept that the different gene complexes of various population groups arose primarily through crossing-over. The Gm^g and Gm^b genes for the γG3-subgroup were extremely closely linked to those for the γG1-subgroup. However the Gm (n) marker indicated that the γG2-subgroup genes were probably further separated on the chromosome. Additional evidence was obtained for the γG2-γG3-γG1-order of the subgroup cistrons. Among the wide range of gene complexes a new type (γG2,—,γ/G1) was described. This complex appeared to have a deletion of the γG3-cistron. Lower levels of γG3-globulin were found in the sera of the individuals with this gene in the heterozygous state. The possibility that this unusual complex arose through an unequal nonhomologous crossing-over is discussed.

Evidence for recent duplications among certain gamma globulin heavy chain genes

A survey of a large number of human sera with the heavy chain genetic markers of the gamma-globulin system has revealed an unusual gene complex which is inherited as a unit through two different families. The gene complex involves two pairs of gammaG1 genetic markers which ordinarily behave as homoalleles, Gm(z) and Gm(f) for the Fd part of gammaG1 molecules, and Gm(a) and non-a for the Fc part. Isolation of the gammaG1 fraction from the unusual sera demonstrated the presence of the important non-a antigen in the gammaG1 fraction. Through the use of immunoadsorbents it was shown that these antigens were not part of a single molecule but that separate molecules were involved. The accumulated evidence indicated that the appearance of such homoalleles on the same chromosome probably resulted from a recent gene duplication, giving rise to two gammaG1 cistrons on one chromosome.

Receptors for human gamma G globulin on human neutrophils

Cell surface receptors for human gammaG antibodies directed against bacterial antigens were demonstrated on human neutrophils using an in vitro bacteriocidal-phagocytic assay. These results were confirmed by adherence of sensitized erythrocytes to monolayers of neutrophils or monocytes. Erythrocytes sensitized indirectly with antibacterial gammaG antibodies after passive sensitization with bacterial antigens adhered to both neutrophils and monocytes. Erythrocytes sensitized directly with conventional anti-D gammaG antibodies adhered only to monocytes, while those sensitized with the hyperimmune anti-CD gammaG antibody Ripley adhered to both monocytes and neutrophils. Adherence of anti-Rh or antibacterial gammaG antibodies to monocytes and neutrophils could be inhibited by whole gammaG, myeloma globulins of the gamma(1) or gamma(3) subclasses, or Fc fragments, but not by Fab fragment. These results indicate that receptors for the Fc portion of human gammaG antibodies exist on both neutrophils and monocytes, and that gammaG antibodies differ in their ability to attach to these two cell types. Differences in the behavior of the gammaG antibodies studied may be related to differences in the density of antibodies on the erythrocyte surface and receptors on the phagocytic cells.

Imbalances of gamma globulin subgroups and gene defects in patients with primary hypogammaglobulinemia

Analysis of immunoglobulin classes, gammaG subgroups, and Gm genetic markers from 59 patients with various types of immune deficiencies was undertaken to assess the function of the several cistrons concerned with synthesis of gamma globulins. 13 patients including two sibling pairs were found to have gammaG subgroup imbalances. All of these patients had non sex-linked disease. 11 of the 13 had preponderance of the gammaG3 subgroup. In most instances of gammaG3 preponderance it was the Gm(b) type of gammaG3 that was selectively retained; the Gm(g) type, controlled by the allelic gene was markedly depressed but not absent in the cases where it could be studied. Other imbalances, either seen concomitantly with gammaG3 preponderance or independently, included predominance of the gammaG2 subgroup and selective absence of single gammaG subgroups.One family was encountered with probable structural gene abnormalities in the autosomal Gm loci. Both parents had different abnormal gene complexes detectable by absence of specific Gm markers and the propositus received both types from the parents. Similar gene complexes have been seen previously in rare instances through population screening but only in the heterozygous state and were not associated with clinically evident hypogammaglobulinemia. Of several other families of patients with subgroup imbalance, two were informative in that structural gene defects could be excluded. Studies on 22 first degree relatives of patients with subgroup imbalances indicated that the most common abnormality detected was in gammaA which was absent in 3 and markedly decreased in 2 others; other abnormalities included decreased levels of specific genetic types of gammaG globulin. It is concluded that gammaG subgroup imbalances are frequently found in non sex-linked immunoglobulin deficiency disorders and in some instances may be associated with family abnormalities suggesting either regulator or structural gene defects.

Anti-globulin antibodies detecting hidden gamma G antigens: characterization of the "pepsin site" by different immune antisera

The antigenic region of human γG-globulin revealed by pepsin digestion has been studied by means of four different `pepsin agglutinator' (PA) containing sera. Two of these were `naturally occurring' agglutinators found in human and subhuman (baboon) sera respectively. The other two were heteroimmune antisera produced by the immunization of rabbits with human and baboon F(ab′)₂ fragments. All of the PAs were agglutinating but not precipitating.

Each PA reacted specifically with γG₁ and γG₃ immunoglobulins as determined by testing with isolated human myeloma proteins. One of the rabbit PAs (RAHPA) reacted with both reduced and unreduced pepsin fragments in contrast to the other agglutinators. In addition, different reaction patterns were evident when the PAs were tested with a panel of pepsin digested primate γG-globulins.

The general trend of the data suggested that a similar antigen was being detected by the four PAs. Further, it was evident that a limited degree of heterogeneity existed within the human `pepsin site' and between similar regions in higher primates.

Naturally occurring pepsin agglutinators in the serum of subhuman primates

Antibodies directed against both human and infrahuman pepsin digested γ-globulin were present in a majority of the primate sera tested. The subhuman pepsin agglutinators paralleled previously described human pepsin agglutinators in respect to their wide distribution in normal sera, their specificity and cross-reactivity, and their immunochemical features. The pepsin agglutinators† at different primate levels appeared closely related.

Among the subhuman pepsin agglutinators a subspecificity was described for a subhuman primate antigen. This finding suggested some limited differences between the subhuman pepsin agglutinators and the human pepsin agglutinators.

Experimental immunization of four cynomologous monkeys failed to elicit or alter these serum reactants.

Two distinct groups of immunoglobulin A(IgA) revealed by peptic digestion

Serum IgA M-components, secretory IgA separated from colostrum, and IgA from serum of patients with cirrhosis of the liver were digested with pepsin at pH 4.1. The IgA M-components segregated into two groups on the basis of their relative rates of peptic digestion. Serum and colostral IgA were digested at a total rate intermediate to that of the two groups of IgA myeloma proteins. It appeared, however, that colostral IgA may have been initially more resistant to peptic digestion than serum IgA. The variability in the rate of peptic digestion was not related to electrophoretic mobility, light-chain type, or IgA subclass. Experimental conditions related to enzyme to substrate ratio or to the pH of the reaction mixture did not appear to explain the differences found.These findings indicate that (a) two groups of IgA proteins can be distinguished on the basis of susceptibility to proteolysis with pepsin, and (b) secretory piece confers, at most, only a minor increase in stability to the IgA molecule against the digestive action of pepsin.

Crossing over between genes in the immunoglobulin heavy chain linkage group of the mouse

Immunoglobulin heavy chain genes were found in wild mice (Mus musculus) that could best be explained as recombinants of immunoglobulin genotypes. In wild mice from Kitty Hawk, N. C., two new heavy chain linkage groups, G(3,5,7,8)H(9,11)F(f)A(-) and G(3,5,8)H(9,11)F(f)A(-), were found, each of which genetically controls both the 3 and 5 distinct immunoglobulin determinants. In inbred strains the 3 and 5 determinants are found independently. The new heavy chain allotype G(3,5,7,8)H(9,11)F(f)A(-) probably arose from a homologous (intragenic) cross-over between G(3,8)H(9,11)F(f)A(-) and G(5,7,8)H(9,11)F(f)A(14) heavy chain linkage groups. It was suggested that genes controlling G(3,8)G(5,7,8), G(3,5,8), and G(3,5,7,8) are alleles. Another homozygous wild mouse (Kyushu, Japan) showed a new heavy chain allotype, (2)G(1,6,7,8)H(9,16)F(s)A(15). The 2 and G(1,6,7,8) determinants are also separated in inbred strains. The 2 determinant in inbred mice is not on the gammaF, gammaH, or gammaA heavy chain and is probably on a gammaG or gammaG-like immunoglobulin heavy chain. Papain digestion of serum from the Kyushu mouse showed two electrophoretically different Fc fragments, one carrying the G(1,6,7,8) and the other the 2 determinant. The new heavy chain allotype, (2)G(1,6,7,8)H(9,16)F(s)A(15), of the Kyushu wild mouse probably arose from a nonhomologous (unequal) cross over between (2)G(-)H(9,16)F(s)A(15) and G(1,6,7,8)H(9,11)F(f)A(12,13,14) heavy chain linkage groups. The linkage group of the Kyushu wild mouse has at least five heavy chain genes, while that of the inbred mice has four.

Serum opsonin, bacteria, and polymorphonuclear leukocyte interactions in subacute bacterial endocarditis. Anti-gamma-globulin factors and their interaction with specific opsonins

The effect of anti-gamma-globulin factors on 7S gamma-globulin opsonins from patients with subacute bacterial endocarditis has been examined with a quantitative in vitro phagocytosis system. Human anti-gamma-globulin factors from patients with subacute bacterial endocarditis and rheumatoid arthritis inhibited the opsonic action of 7S gamma-globulin specifically bound to bacteria. A similar antiopsonic effect was obtained with rabbit antiserum to human gammaG globulin. The antiopsonic effect of anti-gamma-globulin factors did not correlate with their ability to potentiate agglutination of bacteria by 7S antibody. Competition was demonstrated between the antiopsonic effect of anti-gamma-globulin factors and the phagocytosis-promoting action of heat-labile serum factors containing hemolytically active complement.

Studies on human antibodies. VI. Selective variations in subgroup composition and genetic markers

The composition of various isolated antibodies was determined by quantitative analyses for heavy chain subgroups and light chain types. Certain antibodies such as anti-tetanus toxoid and anti-A isoagglutinins were predominantly of the major gammaG1-type. However, a high preponderance of molecules of the minor gammaG2-subgroup was found for antibodies to dextran, levan, and teichoic acid. These findings explain some unusual features previously noted for anti-dextrans such as weak PCA reactions and lack of Gm antigens. Studies of several isolated antibodies from single heterozygous individuals showed a selective absence of genetic markers in certain antibodies and their presence in others. The "allelic exclusion" principle was clearly evident in the isolated antibodies of two different individuals. Large differences in the ratio of kappa to lambda light chains were observed for the same type of antibody from different individuals. Subfractionation of dextran antibodies by affinity for specific glycosidic linkage or combining site size produced marked changes in the ratios. The isomaltohexaose eluates of the dextran antibodies from two subjects were primarily kappa and the isomaltotriose eluates were predominantly lambda. The one anti-levan antibody studied was uniquely homogeneous, consisting exclusively of gammaG2-heavy chains and kappa light chains. By these criteria as well as others, it closely resembled myeloma proteins.