The binding of synovial tissue-derived human monoclonal immunoglobulin M rheumatoid factor to immunoglobulin G preparations of differing galactose content.

There are several sites on IgG Fc that have been reported to be the epitopes for binding rheumatoid factors (RF). It is now established that there are alterations in the oligosaccharides on IgG from patients with rheumatoid arthritis and it has been suggested that these changes may enhance immune complex and cryoglobulin formation. We have used a series of IgG preparations differing in their content of oligosaccharide chains lacking galactose from 18 to 86% to determine whether changes in sugar content affect the binding of rheumatoid factor. Five of 16 monoclonal rheumatoid factors prepared from synovial tissue, from patients with juvenile or adult rheumatoid arthritis, bound better to IgG which was deficient in galactose. Six of the 16 rheumatoid factors from the same patients bound independently of the galactose content. Four of the 16 rheumatoid factors could not be absolutely grouped in this manner but seemed to demonstrate a preference for agalactosyl IgG. One rheumatoid factor bound better to fully galactosylated IgG. There was an association between enhanced binding to galactose-deficient IgG and monoreactivity and a very strong association between the functional affinity of the rheumatoid factors and the dependent binding.

A critical evaluation of the magnetic cell sorter and its use in the positive and negative selection of CD45RO+ cells.

In this paper, we report on our year-long experience with the magnetic cell sorter (MACS), and present a critical evaluation of its pitfalls and benefits. Satisfactory separation of lymphocytes into subsets with preservation of function can be achieved, but there are several drawbacks: in comparison with Dynal beads, MACS results in a higher cell loss due to the increased number of separation steps and requires depletion of plastic-adherent cells as these will engulf microbeads and contaminate the enriched fraction, and is more expensive. The advantage of MACS over Dynal beads is that the microbeads are biodegradable and do not interfere with proliferation assays: both the depleted and enriched fractions of cells can therefore be used in culture immediately following separation. We used MACS for the positive and negative selection of CD45RO cells: the enriched fraction was of high purity (greater than 98%), but a depleted fraction of greater than 90% purity could not be obtained even after running the same sample over three separating columns. Dynabeads, on the other hand, achieved 98% pure CD45RO-depleted fractions after three separation runs.

Framework peptides from kappa IIIb rheumatoid factor light chains with binding activity for aggregated IgG.

Most monoclonal human rheumatoid factors (RF) and some RF from rheumatoid patient's synovia are restricted in their light chains, using predominantly the kappa IIIb subfamily. Very few sequence differences are found between these light chains. Light chains with similar variable region framework sequences are also found in some mouse monoclonal RF derived from mice stimulated with lipopolysaccharide or secondarily immunized with protein antigens. There are two likely explanations for this restriction in framework sequences between the two species: (a) the sequences are important for the immunoregulation of RF production or (b) the sequences are concerned with the antibody binding specificity of the RF. We have examined overlapping octapeptides from the kappa IIIb light chain variable region and show that some framework peptides have the ability to bind aggregated IgG. Replacement of amino acids within the peak binding peptide have indicated the critical amino acids necessary for binding.

Epitope mapping.

The immune response to extrinsic and intrinsic antigens involves specific antigen receptors on T and B cells. The precise antigenic determinants, or epitopes, recognized by these receptors are discrete sequences within the native antigen. The ability to identify and manufacture key epitopes in the immune response has important implications for disease diagnosis and immunointervention. Consequently, increasingly sophisticated technologies are being applied to epitope mapping. This report from a recent workshop gives a balanced view of progress to date and the challenges ahead.

Rheumatoid factors and complex formation. The role of light-chain framework sequences and glycosylation.

New information regarding rheumatoid factors (RFs) indicates that the RFs synthesized in synovium and lymphoid tissues of patients with rheumatoid arthritis (RA) are different from monoclonal and nonspecific RFs associated with other inflammatory states. The characteristics of RF associated with RA are as follows. They are of all Ig isotypes (not just IgM), indicating T-cell participation in antibody maturation. They have higher avidity for human IgG than for rabbit IgG. They use the human germline heavy-chain variable region (VH) gene VHIII more frequently than other VH genes, and light chains from multiple families. (In contrast, monoclonal RFs use predominantly VH1 and very commonly the V kappa IIIb germline gene HUMkv325). RA IgG is somatically mutated. (In contrast, monoclonal RFs use unmutated germline Ig genes). This suggests they are matured by stimulation either with specific antigens or other activation signals such as cytokines. They are abnormally glycosylated. In general, during periods of disease activity in adult and juvenile RA, a galactose is missing from the Fc of the IgG molecule, leaving an empty "pocket" between the C gamma 2 domains of heavy chains. The IgG RFs self-associate. This may result at least in part when galactose on the F(ab')2 portion of one IgG molecule fills the empty pocket in the Fc of another Ig molecule. Self-association forms immune complexes capable of fixing complement and probably of causing joint damage and vasculitis.