ANALYSIS OF IDIOTOPE STRUCTURE OF OVARIAN-CANCER ANTIBODIES - RECOGNITION OF THE SAME EPITOPE BY 2 MONOCLONAL-ANTIBODIES DIFFERING MAINLY IN THEIR HEAVY-CHAIN VARIABLE SEQUENCES
R. Slobbe et al., ANALYSIS OF IDIOTOPE STRUCTURE OF OVARIAN-CANCER ANTIBODIES - RECOGNITION OF THE SAME EPITOPE BY 2 MONOCLONAL-ANTIBODIES DIFFERING MAINLY IN THEIR HEAVY-CHAIN VARIABLE SEQUENCES, Clinical and experimental immunology, 98(1), 1994, pp. 95-103
Two MoAbs, independently raised against ovarian carcinoma cells and re
ferred to as OV-TL3 and OV-TL16, display an identical reaction pattern
with a membrane-associated protein in both normal and malignant ovari
an cells. Also, a similar binding affinity constant and a similar numb
er of binding sites per cell indicate that both MoAbs bind to the same
antigen. Competition assays reveal that OV-TL16 is able to compete wi
th OV-TL3 for binding to OVCAR-3 cells. Epitope mapping using a filame
ntous phage hexapeptide epitope library showed that both MoAbs are abl
e to select identical phages, suggesting that their epitopes are ident
ical or at least overlapping. However, purified polyclonal and monoclo
nal anti-idiotypic antibodies directed against OV-TL3 failed to recogn
ize the OV-TL16 idiotype, indicating that the structure of the antigen
-binding regions of both antibodies is distinct. This was corroborated
by molecular cloning and sequencing of the variable heavy (V-H) and l
ight (V-L) chain immunoglobulin regions of both MoAbs. The V-H regions
of both antibodies were found to be distinct, whereas the V-L regions
are almost identical. Computer modelling of the idiotypes suggests th
at the complementarity determining regions (CDR), with the exception o
f V(H)CDR3, have (almost) identical spatial configurations. Our data i
ndicate that, although structurally different in their V-H regions, OV
-TL3 and OV-TL16 are able to bind to identical epitopic regions on the
antigen, because differences in primary structure do not exclude the
formation of sufficient and similar spatial structures for the interac
tion with an epitope.