Fv Structure of Monoclonal Antibody II-481 Against Herpes Simplex Virus Fcy-binding Glycoprotein gE Contains Immunodominant Complementarity Determining Region Epitopes that React with Human Immunoglobulin M Rheumatoid Factors

Human immunoglobulin M (IgM) rheumatoid factors (RFs) show primary direct enzyme-linked immunosorbent assay (ELISA) reactivity with Fab rather than Fc fragments of monoclonal antibody (mAb) II-481 directed against the Fc3'-binding site of herpes simplex virus glycoprotein gE. This preferential anti-Fab specificity suggests that RFs react with antigen-binding portions of mAb II-481 as anti-idiotypic antibodies directed at the combining site regions of mAb reacting with the Fc3'-binding region of gE. Analysis of this idiotype-anti-idiotype reaction employed polymerase chain reaction amplification and sequencing of the variable heavy and light (VH and VL) regions of mAb 11-481. When VH and VL regions of mAb II-481 were synthesized as overlapping 7-met peptides on polypropylene pins, a panel of 10 polyclonal and 6 rnonoclonal human IgM RFs reacted primarily with epitopes within the three solvent-exposed mAb 11-481 complementarity determining regions (CDRs). Preincubation of single CDR heptamer peptides with IgM RFs in free solution, resulted in 63-100% inhibition of RF binding to mAb II-481 on the ELISA plate, confirming the antigenic importance of linear CDR regions for RF reactivity. Combinations of two or three CDR peptides frequently produced 94-100% inhibition of RF binding to whole mAb II-481. Control peptides, singly or in combination, showed no inhibition. Computer modeling suggested that the R.F-reactive mAb II-481 Fv region and a previously demonstrated R.F-reactive CH3 epitope displayed considerable three-dimensional similarities in conformation. These studies may provide insight into limited shape homologies possibly involved in an R.F anti-idiotypic reaction.