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Biomedical subjects

R Jefferis

Publications and source records attributed to R Jefferis.

At least 55 records · Page 3Linked to original sources
PubMed1995

Oligosaccharide-protein interactions in IgG can modulate recognition by Fc gamma receptors.

X-ray crystal structures of IgG-Fc provide evidence of extensive noncovalent interactions between the protein and carbohydrate moieties, and glycosylation, at Asn-297 within the Fc, has been shown to be important for effector functions mediated through Fc gamma receptors expressed on leukocytes. We have applied protein engineering in an attempt to define protein/carbohydrate interactions essential to wild-type biological activity. We demonstrate that replacement of Lys-246, Asp-249, and Glu-258, which make contacts with GlcNac and Gal on the outer alpha[1-->6] arm, do not affect recognition of human chimeric IgG3 by human Fc gamma RI and Fc gamma RII. However, replacement of Asp-265, which make contacts with the primary GlcNac sugar residue and is covalently attached to Asn-297, resulted in loss of recognition of both Fc gamma RI and Fc gamma RII. Similarly, replacement of Asp-265 in mouse IgG2b resulted in loss of recognition by mouse Fc gamma RII. These results suggest that noncovalent contacts of Asp-265 with the primary GlcNac residue are important for maintenance of recognition of IgG by Fc gamma receptors whereas contacts with GlcNac and Gal on the alpha [1-->6] arm do not have a measurable effect. This conclusion was supported by experiments in which galactose-deficient and fully galactosylated forms of a human IgG4-Fc fragment were shown to be equivalent in their ability to inhibit superoxide generation by IgG4 stimulated U937 cells.

Animals↗
PubMed1995

Activation of effector functions by immune complexes of mouse IgG2a with isotype-specific autoantibodies.

Analysis of five monoclonal autoantibodies, rheumatoid factors produced by hybridomas generated from spleen cells of BALB/c mice repeatedly infected with A/PR/8/34 human influenza A virus, revealed that they recognized distinct but spatially related epitopes. The differing isoallotypic specificity of the IgM and IgA monoclonal antibodies correlated with the presence of Ile258 and Ala305, respectively. Although these data suggest that the epitopes recognized are within the CH2 domain, all antibodies failed to inhibit IgG antigen reactivity with Staphylococcus aureus protein A (SpA), C1q, mouse C3, human Fc gamma RI or mouse Fc gamma RII, activities known to be predominantly determined by CH2 domain structures. Reactivity of the IgA antibody, Z34, with IgG2b allowed further specificity studies using a panel of 26 mutant IgG2b proteins, each having single amino acid replacements over the surface of the CH2 domain. The only substitution that affected Z34 reactivity was Asn/Ala297, which destroyed the glycosylation sequon, resulting in secretion of an aglycosylated IgG molecule. The epitope recognized by Z34 therefore seems to be located outside of the Fc gamma R and C1q binding sites, but to be dependent on the presence of carbohydrate for expression. In contrast to the binding studies, complement activation by aggregated IgG2a, through classical or alternative pathways, was inhibited by the presence of autoantibodies. The functional significance of isotype-specific autoantibody in immune regulation is discussed.

Animals↗
PubMed1994

A novel 13C isotopic labelling strategy for probing the structure and dynamics of glycan chains in situ on glycoproteins.

A protocol is described for uniform 13C labelling of terminal galactose residues of the glycan chains of glycoproteins, using an enzymatic method which does not perturb the protein. The technique is illustrated by application to the biantennary N-linked glycan chains attached at Asn 297 of immunoglobulin G (IgG). Isotope-edited NMR experiments on this glycoprotein yield data which suggest that the galactose residues on the glycan exist in two discrete environments, with the galactose in one environment having greater mobility than that in the other. These data are qualitatively consistent with crystallographic data on an Fc fragment, which suggest that one arm of the glycan is in contact with the protein, while the other projects into the space between the C gamma 2 domains. Quantitatively, however, these data cannot be rationalized with the crystallographic data, which implies subtle differences in oligosaccharide structure and dynamics between the solution and crystal states of Fc.

Carbohydrate Sequence↗
PubMed1994

Characterisation of putative monoclonal anti-G3m(u) and anti-G3m(g) reagents and their antigenic determinants.

Monoclonal antibodies (MAbs) against IgG3 allotypic markers were evaluated in haemagglutination inhibition and IgG3 capture ELISA. MAbs PNF69C and 200D1 exhibited G3m(u) and G3m(g) specificity respectively. In HAI target epitopes detected by MAbs were remarkably stable to physiochemical degradation. Western blotting revealed that MAb 200D1, bound to intact IgG3 heavy chain disease protein and not its pFc' fragment; a result consistent with the CH2 domain location of the G3m(g) allotope. The G3m(u) allotope is also located within this domain. Surprisingly anti-G3m(u) MAb PNF69C bound to the pFc' of IgG3-related protein, HW, and to the pFc' of IgG1-related protein, PR, in Western blot.

Antibodies, Monoclonal↗
PubMed1994

Effects of HIV infection on VH3 (D12 idiotope) B cells in vivo.

The abnormalities of B lymphocytes in human immunodeficiency virus (HIV) infection usually have been attributed to secondary consequences of disturbed immunoregulation. However, recent work has revealed avid binding of HIV gp120 to a conserved immunoglobulin motif unique to the VH3 gene family and the selective gp120-induced activation of VH3 B cells in vitro. This cross-sectional clinical study tests whether HIV infection is associated with a selective response of VH3 B cells in vivo. Levels of blood B cells and serum immunoglobulins (Ig) expressing the D12 idiotope of the VH3 gene family were measured in subjects of the Multicenter AIDS Cohort Study grouped according to clinical stages of HIV infection. A 3-fold elevation in D12 B cells was observed in HIV seropositive versus seronegative groups. This was selective for the D12 population, since total B cell numbers were identical in the two groups. The levels of D12 B cells and CD4 T cells were significantly correlated, and D12 B cells were markedly reduced in the AIDS group (4- and 10-fold, compared to the seronegative and seropositive groups). Analogous differences were also seen in the levels of serum anti-gp120 D12 Ig. This change in VH3 B cells among groups of HIV-infected individuals provides further evidence identifying gp120 as a VH3 B cell superantigen.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Effector mechanisms activated by human IgG subclass antibodies: clinical and molecular aspects. Review article.

Secondary systemic immune responses are predominantly of the IgG class and passive administration of intravenous IgG, from pooled normal serum, is an effective prophylactic and/or therapeutic treatment for patients with defined immunodeficiencies. However, the proportions of each IgG subclass present within a specific antibody response may differ dramatically from that of the total IgG pool. For some antigens the response may be essentially restricted to a single subclass and it may be presumed that the antibody isotype produced has an optimal protective role. The clinical consequences of selective IgG subclass deficiency appears to validate this presumption. In this review we emphasize the differences in effector functions activated by the IgG subclasses and hence the mechanisms responsible for the removal and destruction of antigen/antibody complexes. These studies are relevant to diagnosis and treatment of patients with recurrent infection; the IgG isotype of monoclonal antibodies selected for passive in vivo therapy; the generation of customized antibodies having a pre-determined profile of effector functions and 'immuno-direction' with new vaccines to provoke an antibody response having an isotype profile optimal for the proposed application.

Complement Activation↗
PubMed1993

Lymphoproliferation in primary Sjögren's syndrome. Evidence of selective expansion of a B cell subset characterized by the expression of cross-reactive idiotypes.

OBJECTIVE: To evaluate the possibility that lymphoproliferation in primary Sjögren's syndrome (SS) arises within a subset of B cells. METHODS: A panel of monoclonal antibodies (MAb) specific for rheumatoid factor (RF)-associated cross-reactive idiotypes (CRI) and anti-V kappa and anti-VH subgroup antibodies were used to define the clonality of B lymphocytes undergoing neoplastic transformation in 5 patients with primary SS. Anti-CRI antibodies were also used to study longitudinal variations in serum paraprotein levels and in vitro regulation of IgM and IgM-RF production by peripheral blood lymphocytes. The levels of CRI, IgM, and IgM-RF were quantitated in serum and culture supernatants by enzyme-linked immunosorbent assay. Heavy and light chain isotypes and VH subgroups of the paraproteins were determined by immunoelectrophoresis, immunofixation, and Western blotting. RESULTS: Paraproteins from all patients expressed an epitope associated with V kappa IIIb sub-subgroup of light chains. Three of the paraproteins were cryoglobulins with RF activity, all of which expressed the V kappa IIIb-associated CRI (detected by MAb 17-109) and the VHI-associated CRI (detected by MAb G6 and G8). None of the paraproteins expressed the VHIII-associated CRI (detected by MAb B6 and D12). The CRI were consistently expressed over a period of 5-6 years. The anti-CRI and anti-subgroup antibodies substantially inhibited spontaneous production of IgM-RF and IgM by peripheral blood B lymphocytes from 3 of the SS patients. CONCLUSION: These results suggest that lymphoproliferation in primary SS is highly selective, and that the anti-CRI antibodies can be used as an aid to early diagnosis as well as for monitoring and modulating the lymphoproliferative process in primary SS.

Adult↗
PubMed1993

Engagement of CD40 lowers the threshold for activation of resting B cells via antigen receptor.

Cross-linking of surface Ig (sIg) on resting B cells can generate intracellular signals; however, for T-dependent antigens to promote growth and differentiation additional surface receptors must be engaged. Ligation of CD40 can stimulate B cell proliferation in the presence of interleukin-4. A recently identified counterstructure for CD40 is found on T helper cells and is believed to represent the cognate ligand for B cell activation. This study investigates the role of CD40 as an accessory molecule in sIg-dependent B cell activation. Simultaneous ligation of sIg and CD40 by monoclonal antibodies (mAb) in the presence of mouse L cells which express human Fc gamma receptor type II (Fc gamma RII-L cells) results in potent stimulation of small resting B cells. When CD40 is co-ligated, picomolar concentrations of mouse IgG1 anti-mu, and anti-delta mAb can stimulate B cell proliferation. This requires interaction of the anti-Ig mAb with the Fc gamma RII-L cells: a mouse IgG2a anti-mu mAb which is not recognized by Fc gamma RII, was > or = 1000-fold less effective. These findings suggest a mechanism for B cell activation whereby engagement of T cells via CD40 and its cognate ligand provides potent enhancement of signals delivered through sIg. Based on these observations, models for the activation of B cells by T-dependent antigens are presented.

Antibodies, Monoclonal↗
PubMed1993

Immunophenotypic and idiotypic characterisation of the leukaemic B-cells from patients with prolymphocytic leukaemia: evidence for a selective expression of immunoglobulin variable region (IGV) gene products.

B-cell prolymphocytic leukaemia (B-PLL) is a rare chronic lymphoproliferative disease characterised by a massive splenomegaly associated with a mild or no lymphadenopathy and a high leukocyte count, mostly representing prolymphocytic features. We have studied membrane expression of certain Ig VK and VH gene products in five patients with B-PLL using a panel of monoclonal anti-subgroup and anti-cross-reactive idiotype (CRI) antibodies. Membrane expression of leukocyte-associated markers has also been investigated. The leukaemic cells from four patients expressed VKIII and VKIIIb subgroup and sub-subgroup kappa light chains. The VKIIIb and VHI-associated CRI identified by the monoclonal antibodies (MoAb) 17-109 and G8 were co-expressed in one patient. No B-cells from the patients expressed the VHIII-associated CRI. The same pattern of CRI expression was observed in a serum paraprotein collected from one of the patients. These results suggest a biased selection for the IG VKIII and VKIIIb light chains in B-PLL.

Aged↗
PubMed1993

Aglycosylated chimaeric human IgG3 can trigger the human phagocyte respiratory burst.

This study investigates the capacity of a complexed aglycosylated chimaeric human IgG3 antibody to induce the respiratory burst in human monocyte-like U937 cells. It demonstrates that the aglycosylated antibody, prepared by cell culture in tunicamycin, retains significant capacity to trigger this effector function which was assayed as superoxide generation. Erythrocytes sensitized with near maximal levels of aglycosylated IgG3 were able to trigger > 80% of the superoxide generation triggered by the glycosylated antibody from U937 cells induced to differentiate by interferon gamma and the aglycosylated IgG3 gave half maximal responses at sensitization levels only 72% higher than those required by the glycosylated form. Aglycosylated IgG3 was, however, much less effective in triggering superoxide generation by interferon gamma treated U937 cells at low sensitization levels as threshold responses required only 60 glycosylated IgG3 molecules per erythrocyte compared with 16,000 aglycosylated molecules. In addition, these studies indicate significant differences between the target cell to effector cell ratios which permit IgG sensitized erythrocytes to stimulate the respiratory burst and those which stimulate ADCC in the same effector cell type.

Dose-Response Relationship, Immunologic↗
PubMed1993

Restricted immunoglobulin variable region gene usage by hybridoma rheumatoid factors from patients with systemic lupus erythematosus and rheumatoid arthritis.

Rheumatoid factors (RFs) are autoantibodies that are produced by approximately 75% of patients with rheumatoid arthritis (RA). Their role in pathogenesis is not well understood. In this study of 81 human hybridoma IgM antibodies derived from unstimulated peripheral blood B-cells of patients with RA and systemic lupus erythematosus (SLE), we have demonstrated that idiotypes associated with RFs derived from patients with mixed cryoglobulinemia were expressed by approximately 60% of RFs and 6% of IgM antibodies lacking RF activity. The specificity of the RFs for the Fc portion of IgG only (monospecificity) or for Fc and additional self antigens (polyreactivity) was found to correlate with the expression of specific heavy chain associated idiotypes. The VH3 associated RF idiotypes, D12 and B6, were expressed by 0/16 (0%) of monospecific RFs compared with 6/22 (27%) of polyreactive RFs. The predominant use of VH3 was verified by analysis of the expressed Ig with VH family specific anti-peptide antibodies. The light chains expressed by both populations of IgM RFs were found to be predominantly VKIII, both by detection of specific epitopes/idiotypes and V family analysis. This non-random gene usage of both the heavy and light chains suggests that there is a selective expression of V regions in the RF producing B-cells in patients with RA and SLE. We suggest that different antigen-driven, clonal selection events may occur which result in either monospecific RFs or polyreactive RFs.

Arthritis, Rheumatoid↗
PubMed1993

Human Fc gamma RI triggering of the mononuclear phagocyte respiratory burst.

This study investigates the role played by Fc gamma RI and Fc gamma RII in triggering the respiratory burst induced in human monocyte-like U937 cells by monoclonal chimaeric anti-NIP antibodies expressing the human IgG subclass and mouse IgG2b heavy chains. Respiratory burst activity was measured as superoxide generation. Four separate lines of evidence indicate a predominant role for Fc gamma RI in triggering superoxide generation induced by erythrocytes sensitized with up to the maximum of 100,000 IgG molecules per cell. Firstly, erythrocytes sensitized with mouse IgG2b anti-NIP antibodies which are not recognized by human Fc gamma RI, did not induce a response but when residue Glu-235 was replaced by Leu to give the lower hinge sequence of mouse IgG2a which is recognized by Fc gamma RI, the mutant bound to Fc gamma RI and induced a response equal to 80% of that given by chimaeric human IgG3. Chimaeric human IgG3 antibodies with amino acid substitutions in the lower hinge showed reduced activity and the greatest reductions (< 32% of wild type antibody activity) were associated with changes at Leu-235 which is critical for recognition by Fc gamma RI. Secondly, chimaeric human IgG4 antibodies which are not recognized by Fc gamma RII, were able to induce superoxide generation. The rank order of abilities of chimaeric human IgG subclass antibodies to induce responses was IgG3 > IgG1 > IgG4 > > IgG2. Thirdly, responses induced by chimaeric human IgG were inhibited by concns of monomeric human IgG3 in the nM range. Finally, chimaeric human IgG3 induced responses were inhibited by anti-Fc gamma RI, but not anti-Fc gamma RII monoclonal antibodies. Consistent with a major role for Fc gamma RI in triggering the responses of U937 cells, erythrocytes sensitized with chimaeric human IgG3 did not induce superoxide generation by neutrophils which express Fc gamma RII and Fc gamma RIII, or eosinophils which express Fc gamma RII, but neither of which expresses Fc gamma RI.

Antibodies, Monoclonal↗
PubMed1993

Control of IgG/Fc glycosylation: a comparison of oligosaccharides from chimeric human/mouse and mouse subclass immunoglobulin Gs.

Oligosaccharide profiles were obtained for chimeric mouse-human antibodies corresponding to each of the human IgG subclasses 1-4, and mouse IgG2b antibodies each expressed in the mouse J558L cell line. These antibodies have specificity for the NIP hapten and form a matched set of IgGs. An IgG4 chimeric antibody (B72.3) produced in the chinese hamster ovary (CHO-K1) cell line was also analysed for carbohydrate. Additionally aglycosylated mutants of this IgG4 (B72.3) and anti-NIP mouse IgG2b were analysed. The total lack of carbohydrate found in the aglycosylated site-directed mutants human chimeric IgG4 B72.3 (Asn 297-->Gln) and mouse IgG2b (Asn 297-->Ala) demonstrates that there are no N-glycosylation sites other than Asn 297. Therefore glycosylation profiles for all the IgGs analysed reflect carbohydrate attached to this site. Factors such as cell type (A), template direction by the IgG heavy chains (B) and culture conditions (C) are shown to influence IgG glycosylation profiles. (A) The anti-NIP IgG antibodies expressed by the J558L cell line may have one or two Gal (alpha 1-->3) Gal residues per oligosaccharide unit, indicative of the presence of (alpha 1-->3) galactosyl transferase in the J558L mouse cell line. (B) The galactosylation profiles obtained for the IgG heavy chains, in particular the preference for galactosylation of the Man (alpha 1-->6) arm rather than the Man (alpha 1-->3) arm, contrary to the beta-galactosyltransferase specificity, suggest that the polypeptide chain may act as a template to influence the extent of galactosylation and hence the proportions of each oligosaccharide incorporated. The IgG2 antibody does not display this galactosylation preference. (C) The extent of galactosylation appears to be influenced by the growth conditions, with the highest levels of galactosylation being found for IgG produced by cells grown in still cultures, rather than cells grown as ascites or in hollow fibre bioreactors. It is concluded that though the profile of glycosylation is controlled predominantly by the glycosylation activity of the cell in which the IgG is expressed, differences between the IgG heavy chain templates of the various subclasses and culture conditions can also influence glycosylation.

Animals↗
PubMed1993

What is an idiotype?

Idiotypy is an important concept with significant practical implications for the manipulation of B- and T-cell clones. However, this potential depends on a correct identification of idiotypy and the development of appropriate reagents. Current knowledge of the structure and polymorphism within the Ig loci reveals that several idiotypic paradigms are based on isotypic or allotypic structures rather than supposed crossreactive idiotypes.

Animals↗
PubMed1993

A quantitative ELISA for measurement of rheumatoid factor associated cross-reactive idiotypes in serum from patients with rheumatic diseases.

A sensitive ELISA for the quantitation of RF associated cross-reactive idiotypes (CRI) has been developed. CRI bearing IgM was captured by immobilized F(ab')2 fragments of monoclonal anti-CRI antibodies and revealed with isotype specific conjugates. Factors affecting sensitivity, specificity and reproducibility of the assay were assessed. The sensitivity limit was less than 10 ng/ml and the linear assay range for the CRI standard curve was from 80 to 500 ng/ml. Using this ELISA system we have quantitated serum levels of the CRI in different groups of patients with RA, early synovitis and normal individuals. Our results indicate a significant increase in the levels of the CRI in the patient groups compared to the normal subjects tested, and suggest involvement of a diverse repertoire of Ig variable region germline genes and/or somatic mutation in production of polyclonal RF in RA.

Cross Reactions↗