Fv structure of monoclonal antibody II-481 against herpes simplex virus Fc gamma-binding glycoprotein gE contains immunodominant complementarity determining region epitopes that react with human immunoglobulin M rheumatoid factors

Rheumatoid factor in idiotypic regulation of autoimmunity

AIM

Rheumatoid factor (RF) is known to be heterogeneous, and RFs detected by various methods exhibit different characteristics. In addition to interacting with the Fc region of immunoglobulin G (IgG), certain RFs are able to recognize idiotypes of antibodies. Given the important role of idiotypic interactions in regulating autoimmunity, we hypothesize that RF is involved in regulation of lymphocyte activity against autoimmune disease-inducing antigens via idiotype-anti-idiotype interactions with these lymphocytes.

METHOD

RF level and the existence of idiotype-anti-idiotype interactions between RF and antibodies to autoimmunity-inducing antigens were studied in rats resistant and sensitive to collagen-induced arthritis, encephalomyelitis and atherosclerosis. RF was assayed by agglutination of tanned IgG-loaded erythrocytes.

RESULTS

Rat resistance to autoimmune disease is associated with high RF production during the initiation of the immune response, and a low RF level during this period may be a preclinical marker of experimental autoimmune disease manifestation. RF-containing sera compete with an antigen if the RF-containing sera were obtained from rats immunized with that antigen, and they non-specifically inhibit binding of different antigen-antibody pairs. This suggests that RFs are anti-idiotypic antibodies that carry two kinds of paratopes: a particular paratope that recognizes the antigen-binding sites of antibodies, and a shared paratope that serves to recognize the recurrent idiotype on antibodies. Antigenic epitopes for the shared RF paratope can be created in the hinge region of Fc fragments of homologous IgG.

CONCLUSION

RF detected by agglutination of tanned IgG-loaded erythrocytes is involved in negative idiotypic regulation of lymphocytes specific to autoimmunity-inducing antigens.

Cross-reactivity of human IgG anti-F(ab')2 antibody with DNA and other nuclear antigens

OBJECTIVE

To characterize immunologic specificity and possible antiidiotype activity of IgG anti-F(ab')2 in normal subjects as well as in patients with active and inactive systemic lupus erythematosus (SLE).

METHODS

IgG anti-F(ab')2 and anti-double-stranded DNA (anti-dsDNA) were affinity isolated from immunoadsorption columns of F(ab')2 and dsDNA linked to Sepharose 4B. Affinity-purified IgG anti-F(ab')2 (APAF) and affinity-isolated IgG anti-dsDNA (APAD) were tested by enzyme-linked immunosorbent assay (ELISA) for other cross-reacting specificities including anti-Sm, anti-Sm/RNP, and anti- Crithidia binding. Anti-DNA specificity of APAF and APAD was assayed by S1 nuclease treatment of heat-denatured DNA. Rabbit antiidiotypic antisera were prepared by immunization with APAF and APAD from normal subjects and SLE patients and absorption with insolubilized human Cohn fraction II (Fr II). VL and VH regions of 5 monoclonal IgM antibodies with anti-F(ab')2/anti-DNA specificity generated by Epstein-Barr virus B cell stimulation were sequenced by polymerase chain reaction and characterized for VH and VL subgroup. APAF and APAD were also examined by high-resolution electron microscopy for possible ring forms indicative of antiidiotypic V-region interactions.

RESULTS

APAF from normal subjects, representing 0.08-0.18% of serum IgG, showed striking relative concentrations of both anti-F(ab')2 and anti-DNA, as well as anti-Sm and anti-Sm/RNP ELISA reactivity. Both APAF and APAD reacting with F(ab')2 or dsDNA on the ELISA plate could be cross-inhibited by F(ab')2 or DNA in solution. Anti-DNA reactivity in normal APAF and APAD was much more sensitive to S1 nuclease treatment than similar fractions from SLE patients. Neither APAF nor APAD from controls produced positive antinuclear immunofluorescence or positive Crithidia staining, whereas these were strongly positive using SLE APAF and APAD. Absorbed rabbit antisera against normal or SLE APAF and APAD showed strong ELISA reactivity against both APAF and APAD, but no residual reactivity with normal Fr II. VL and VH sequencing of monoclonal human IgM antibodies showing both anti-F(ab')2 and anti-DNA reactivity showed relative VH3, V kappa 1 or VH1, V kappa 3 restriction. No evidence of ring forms or V-region "kissing" dimers was obtained when normal or SLE APAD or APAF was examined by high-resolution electron microscopy.

CONCLUSION

IgG anti-F(ab')2 in both normal subjects and SLE patients represents a polyreactive Ig subfraction with concomitant anti-DNA, anti-Sm, and anti-Sm/RNP specificities. Anti-DNA reactivity in SLE is qualitatively different from that in normal APAD and APAF since normal APAD and APAF anti-DNA is much more sensitive to S1 nuclease digestion of denatured dsDNA. APAF and APAD share distinct V-region antigens which may be related to prominent VH3 or VH1 antigenic components. No evidence for in vivo complexing of anti-DNA and anti-F(ab')2 as ring forms or antiidiotype-IgG complexes was observed during ultrastructural studies. In both normal individuals and SLE patients, APAF may represent a small polyreactive IgG subfraction which also contains antinuclear and anti-DNA specificities.

Molecular localization of human IgG anti-F(ab')2 reactivity with variable- and constant-region lambda light-chain epitopes

Human IgG antibodies reacting with antigenic determinants on F(ab')2 fragments represent generic antiidiotypic antibodies present in the serum of normal individuals. Additionally, the titers of these antibodies in the sera of patients with systemic lupus erythematosus (SLE) are inversely related to disease activity. Because these autoantibodies recognize predominantly light chain-related epitopes, especially lambda type, we synthesized constant (C)lambda- and variable (V)lambda-related overlapping 7-mer peptides on polypropylene pins to determine anti-F(ab')2-reactive epitopes on human lambda light chains. ELISA reactivity of affinity-purified anti-F(ab')2 antibodies obtained from normal individuals and from patients with SLE, as well as murine anti-human light-chain monoclonal antibodies specific for C lambda and V lambda subgroup-related determinants, was tested using the overlapping 7-mers of human lambda light-chain sequence. The patterns of reactivity against C lambda-related peptides were similar in both normal and SLE-derived anti-F(ab')2 antibodies. However, reactivity profiles against V lambda-related peptides were distinctively different between the normal and the SLE-associated anti-F(ab')2 autoantibodies. A decrease in reactivity among the SLE IgG anti-F(ab')2 antibodies was noted for particular amino acid V lambda complementarity-determining region (CDR) residues, including glycine at positions 27 and 54, alanine at 16 and 37, and tyrosine at 28 and 91. This different pattern of reactivity from normal may indicate that in SLE there is a failure of antiidiotypic control mechanisms, as reflected by a defect in production of antibody to immunodominant V lambda CDR residues.