Hulya Kaymaz

Antigenic mapping of a human λ light chain: Correlation with three dimensional structure

Although the amino acid sequence and three-dimensional structure of human immunoglobulin light chains have been known for more than 15 years, the location of antigenic markers characteristic of λ chains has not been determined. Here, we use a set of synthetic overlapping peptides to completely model the sequence of the λ chain Mcg and test these for the binding or rabbit and goat antisera specific for λ chain determinants. We assess peptide contributions to λ-antigenic reactivity and also to identify a portion of C-region where conformational factors contribute to the antigenicity. Specific determinants occur both in the constant and variable (first and third framework) domains of the molecule. The fourth framework of the variable region, a segment specified by the joining gene, is also recognized and cross-reacts antigenically with the homologous region of T cell receptor β chains. Major λ specific determinants are localized in the N- and C-terminal segments, which are linear and devoid of major conformational folding. Other segments that are strongly antigenic, such as the third framework of the V region (residue 78–93) and a segment of the constant region (residues 177–192), show strong conformational dependence in antigenicity.

Lack of preferential Vβ usage in synovial T cells of rheumatoid arthritis patients

The T-cell receptor Vβ subfamily repertoires of synovial and peripheral T cells of 8 rheumatoid arthritis (RA) patients were determined using the polymerase chain reaction. Three normal controls were included. Some of the rheumatoid synovial samples did not express the complete range of Vβ families and lacked as many as 6 gene families. However, these patients showed considerable individual variation in expression. Overall, the data do not support preferential T-cell receptor Vβ usage in synovial T cells of RA patients either in comparison to their autochthonous peripheral T cells or to peripheral T cells of normal subjects.

Naturally Occurring Human Autoantibodies to Defined T-Cell Receptor and Light Chain Peptides

We used synthetic peptides duplicating the structures of a human lambda light chain (Mcg), and a human T-cell receptor (Tcr) alpha and a Tcr beta chain predicted from gene sequence to determine the presence and loci of activity of natural human autoantibodies directed against these antigen recognition molecules. We report that normal individuals and patients suffering from autoimmune diseases have antibodies directed against regions of lambda light chains and Tcr beta chains corresponding to the first complementarity determining region and the third framework region of the variable domain and to constant region determinants. The levels of IgM natural antibodies particularly against the CDR1 peptides tend to be higher in RA patients than in normals or SLE patients. Although polyclonal IgG immunoglobulins from healthy individuals did not show detectable reactivity to Tcr alpha peptides, such reactivity was found in the IgM immunoglobulins of RA patients, thereby showing that Tcr alpha peptides can be autoantigenic in man. The levels of IgM autoantibodies to V beta CDR1 peptides tend to decrease with age. By contrast, there was a marked increase in IgG natural autoantibodies to certain CDR1 sequences with advancing age. We suggest that the natural antibodies to defined regions of immunoglobulins and T-cell receptors are part of a physiological network for the regulation of the immune response.

Autoreactive sites of human lambda light chain mapped by comprehensive peptide synthesis.

Autoantibodies reactive against immunoglobulins are associated with autoimmune disorders as well as with immunization and infection. Moreover, recent interest is focused on auto-antidiotypes because of their possible role in immunoregulation. In this study, we used a set of overlapping synthetic peptides duplicating the structure of the monoclonal human λ light chain Mcg to map autoreactive dterminants recognized by natura lantibodies present in normal polycolonal human IgG. We found that autoantibodies in human IgG react strongly with two distinct Vλ determinants corresponding to the first complementarity determining region (CDR1) and the third framework (Fr3). Antibodies showing weak reactivities against three regions of the constant domain also occur in the preparations. The antibodies directed against light chain peptides comprise less than 0.1% of the IgG pool. Analysis by direct binding and by competitive ELISA inhibition established that affinity purified antibodies specific for CDR1 and Fr3 peptide determinants react with the intact light chain Mcg as well as with the corresponding peptide. Competitive inhibition studies comparing total IgG and affinity-purified antibodies indicate that natural antibodies showing a wide range of affinities are present. The polyclonal nature of the natural antibodies is further shown by the presence of both κ and λ light chains in the purified antibodies. Although the role of such natural antibodies remains to be determined, the cross-reactivity between Vλ peptides and the intact chain suggest that they can function in regulation of antibody formation.

Light and heavy chains specifying a human IgMκ autoantibody to a T-cell receptor Vβ-antigen

Abstract Humans frequently produce serum IgM autoantibodies reactive with T-cell receptor β chains at a determinant defined by peptides corresponding to the first complementarity determining region. It is likely that this determinant serves as a public idiotype involved in immunoregulation. Following screening of culture supernatants from over 60 Epstein-Barr virus-carrying B-cell lines of normal and neoplastic origin, we identified a line, IARC307, that secretes an IgMκ protein showing marked specificity for the Vβ8.1 CDR1 sequence CKPISGHNSLFQWYRQT. We cloned and sequenced the complete variable regions of the Vκ and V H chains used by the autoantibody. The light chain has a VκIII sequence related to the ‘a’ subgroup and uses Jκ2. The heavy chain has a V H III sequence essentially identical to the germline sequence DP54 and uses the J H 6C minigene. The CDR3 is unique, differing from those of other autoantibodies. The antibody is rigorously specific in its specificity for the Vβ8 peptide and does not show polyspecificity for protein or DNA antigens.