Isotype restriction of idiotopes associated with human anti-streptococcal A carbohydrate antibodies

Manipulation of the glycan-specific natural antibody repertoire for immunotherapy

Natural immunoglobulin derived from innate-like B lymphocytes plays important roles in the suppression of inflammatory responses and represents a promising therapeutic target in a growing number of allergic and autoimmune diseases. These antibodies are commonly autoreactive and incorporate evolutionarily conserved specificities, including certain glycan-specific antibodies. Despite this conservation, exposure to bacterial polysaccharides during innate-like B lymphocyte development, through either natural exposure or immunization, induces significant changes in clonal representation within the glycan-reactive B cell pool. Glycan-reactive natural antibodies (NAbs) have been reported to play protective and pathogenic roles in autoimmune and inflammatory diseases. An understanding of the composition and functions of a healthy glycan-reactive NAb repertoire is therefore paramount. A more thorough understanding of NAb repertoire development holds promise for the design of both biological diagnostics and therapies. In this article, we review the development and functions of NAbs and examine three glycan specificities, represented in the innate-like B cell pool, to illustrate the complex roles environmental antigens play in NAb repertoire development. We also discuss the implications of increased clonal plasticity of the innate-like B cell repertoire during neonatal and perinatal periods, and the prospect of targeting B cell development with interventional therapies and correct defects in this important arm of the adaptive immune system.

Association of placental transfer of anti-Haemophilus influenzae type b polysaccharide antibodies with their V regions

Immunization of mothers during pregnancy may be an effective means of providing protection to infants during the first months of life against many pathogens. Previous studies have identified factors that influence the transfer of immunoglobulin across the placenta, including the time of vaccination during pregnancy and isotypes of specific immunoglobulins. By studying antibodies to Haemophilus influenzae type b polysaccharide (Hib-PS) in 26 pairs of maternal-cord sera obtained from unimmunized healthy women and 22 pairs of maternal-cord sera from women immunized with one of three different Hib vaccines, we have found that the immunoglobulin transfer is also dependent on the V region of antibodies. Anti-Hib-PS derived from the V kappa II gene "A2" was transferred about ten times more efficiently to the fetus than other anti-Hib-PS antibodies (20% vs 1-2%). It was found that antibodies derived from the A2 V kappa gene are primarily IgG whereas other antibodies are preferentially associated with the IgM isotype. The potential association between the antibody V region with preferential placental transfer should be considered for future studies involving maternal immunization.

Human immunoglobulin G (IgG) Fc receptor IIA (CD32) polymorphism and IgG2-mediated bacterial phagocytosis by neutrophils

Human immunoglobulin G (IgG) Fc receptor IIa (Fc gamma RIIa; CD32) is expressed on phagocytes, triggers phagocytosis, and represents the sole Fc receptor for IgG (Fc gamma R) capable of interaction with IgG2, the main IgG subclass induced in response to bacterial capsular polysaccharides. The two genetically determined structurally different allotypes of human Fc gamma RIIa, the products of the Fc gamma RIIa-R131 and IIa-H131 alleles, have functionally different reactivities with human IgG2. In humans, the Fc gamma RIIa-H131 allotype is known to interact efficiently with complexed human IgG2, whereas the IIa-H131 allotype does so only poorly. This polymorphism may therefore have implications for IgG2-mediated phagocytosis of encapsulated bacteria and susceptibility to bacterial infections. Phagocytosis of IgG2-opsonized bacteria by homozygous Fc gamma RIIa-R/R131, heterozygous IIa-H/R131, and homozygous IIa-H/H131 polymorphonuclear cells (PMN) was compared. A higher phagocytic capacity of IgG2-opsonized group B type III streptococci by PMN of homozygous H/H131 individuals compared with PMN from homozygous R/R131 individuals was observed (P = 0.001), while heterozygous IIa-H/R131 PMN showed intermediate phagocytosis. In this model system, IgG2-mediated phagocytosis was independent of the Fc gamma RIIIb-NA1/NA2 allelic polymorphism.

Ontogeny of the humoral response to group A streptococcal carbohydrate: class and IgG subclass composition of antibodies in children

We determined isotypes of natural antibodies to streptococcal group A carbohydrate (A-CHO) in sera from 101 children between 1 and 16 years of age, using a calibrated enzyme-linked immunosorbent assay system. Anti-A-CHO IgM could be detected in all but one sera. Median levels increased with age and were highest between 8 and 12 years. IgG antibodies were present at low concentrations up to the age of 4 years, and consisted predominantly of the IgG1 subclass. Between 4 and 8 years, concentrations of anti-A-CHO IgG markedly increased and median levels continued to increase through age 12-16. Anti-A-CHO IgG1 levels closely followed the pattern of IgG antibody concentrations. The number of IgG2 antibody positive sera was low in young children, as expected. In the 8-12 year age group and later, anti-A-CHO IgG2 was present in more than half of the samples, and in children between 12 and 16, medians of IgG2 and IgG1 antibodies were similar. Sera containing anti-A-CHO IgG3 were rare in children up to 4 years of age, but in the group of 4-8-year-old children, this subclass was detectable in 36% and later in up to 77% of the sera. Thus, the IgG response to A-CHO showed a clear maturation during childhood, involving the subclasses IgG1, IgG2 and IgG3. There were no significant differences in A-CHO levels between boys and girls.

Human immune response to group A streptococcal carbohydrate (A-CHO). III. Comparison of the efficiencies of anti-idiotopic antibody and of nominal antigen in the induction of IgM anti-A-CHO-producing B cells

In this study the efficiencies of a monoclonal anti-idiotopic (Id) antibody (anti-Id498) and of various preparations of nominal antigen in the induction of an antigen-specific human B cell response in vitro were compared. Anti-Id498 recognizes a recurrent, binding site-related Id present on IgM antibodies with specificity for N-acetyl-D-glucosamine, the immunodominant group of streptococcal group A carbohydrate (A-CHO). We have previously shown that anti-Id498 induces IgM anti-A-CHO secretion from B cells of donors that possess Id-498+ antibodies in their serum. A-CHO was presented to B cells either in soluble or insoluble form, i.e. coupled to beads or as intact bacteria. Purified blood B cell populations from three Id+ healthy donors with high numbers of circulating anti-A-CHO B cells were used and antibody-producing B cells are enumerated in a single-cell assay (spot ELISA). The data show that anti-Id498 was superior in the induction of IgM anti-A-CHO-secreting B cells in two donors (factor 4.6 and 13.5 as compared to the most efficient antigenic stimulation). In the third donor antigen stimulation was slightly more efficient than anti-Id but only with Sepharose-bound A-CHO and not with soluble A-CHO or intact bacteria. The increase of specific B cells induced after stimulation with anti-Id498 could be abolished after addition of autologous T cells in two donors. On the contrary, an enhancement of the specific response was observed after addition of autologous T cells in antigen-stimulated cultures. Neither suppression nor enhancement were induced by addition of irradiated T cells.

Human immune response to allergens of house dust mite, Dermatophagoides pteronyssinus. V. Auto-anti-idiotypic antibody characterization and cross-reactivity

From the serum of 10 allergic subjects we have prepared IgG antibodies recognizing idiotopes carried by specific antibodies to Dermatophagoides pteronyssinus (Dpt) allergens, and studied cross-reactivity of anti-Dpt IgG bystander and antigen-binding site-associated idiotopes by latex agglutination assays. Idiotopes of specific anti-Dpt IgE were evaluated by radioimmunoassays. Depending on the assay, a binding or inhibition of more than 50%, as compared to the reactivity of specific antibodies with the corresponding anti-idiotypic (anti-Id) IgG, was considered significant. Cross-reactivity of antigen-binding site-associated idiotopes attained a mean proportion of 6/10 for IgG and 9.6/10 for IgE. By contrast, bystander idiotopes cross-reacted only occasionally with a mean proportion of 2/10 for both IgG and IgE antibodies. Anti-Id antibodies from two subjects have been isolated by adsorption on insolubilized anti-Dpt antibodies of the corresponding patient. Using this purified material we have confirmed that (a) the majority of anti-Id antibodies carry an "internal image" of the initial antigen and compete in a dose-dependent manner with Dpt allergens for the binding to the anti-Dpt antibodies and (b) paratope-associated idiotopes of anti-Dpt antibodies are shared by unrelated individuals.

Human immune response to allergens of house dust mite, Dermatophagoides pteronyssinus. III. Cross-reactivity of bystander idiotopes on allergen-specific IgE antibodies

Rabbits were inoculated with affinity-purified human antibodies to the common house dust mite Dermatophagoides pteronyssinus (DPT) to produce anti-idiotypic (Id) antibodies. The Id carried by human IgE antibodies were studied in a radioimmunoassay in which specific anti-DPT IgE were first insolubilized on rabbit F(ab')2 fragments against human Fc epsilon. In a single individual specific anti-DPT IgE antibodies shared bystander idiotopes (i.e. idiotopes located outside the antigen-binding site) with IgG antibodies of the same specificity, since the adsorption on insolubilized anti-DPT IgG almost completely eliminated the binding of anti-Id antibodies to IgE. This differed from our previous observations (J.-M. R. Saint-Remy et al., Eur. J. Immunol. 1986. 16: 575) wherein distinct paratope-associated idiotopes were identified on IgG and IgE anti-DPT antibodies. The frequency of cross-reactions between idiotopes of anti-DPT IgE antibodies observed in ten unrelated individuals was less than 10% for bystander idiotopes. This finding confirmed the private character of the above idiotopes that we found earlier on anti-DPT IgG antibodies. However, one anti-Id antibody preparation was found to react with bystander idiotopes of anti-DPT IgE of most individuals, thereby suggesting the existence of a recurrent idiotope. The low frequency of inter-individual bystander idiotope cross-reactivity contrasted with the public character of paratope-associated idiotopes.