Network of idiotypic and anti-idiotypic antibodies related to the ovarian carcinoma-associated folate binding protein

The present paper describes the generation and characterization of anti-idiotypic monoclonal antibodies (Ab2 MAbs) produced against the MOv19 MAb (Ab1 MAb), which shows a restricted reactivity with human ovarian carcinoma. The Ab2 MAbs were produced by immunizing mice with MOv19 conjugated to syngeneic mouse red blood cells (MRBC). After the somatic hybridization, five Ab2 MAbs, designated Id19.1, Id19.2, Id19.3, Id19.4 and Id19.5, were selected by a sandwich assay on the basis of their specific reactivity to the MOv19 MAb, but not to the isotype-matched MAb used as a control. A complete cross-inhibition between these 5 MAbs was observed, indicating that they recognize overlapping idiotopes on MOv19. The Ab2/antigen relationship of two Ab2 MAbs (Id19.1 and Id19.2) was investigated by competition experiments on a relevant tumor target cell line. We showed that both Ab2 MAbs were able to interfere with the antigen binding capacity of ¹²⁵I-MOv19. Moreover, Id19.1 was able partially to inhibit the binding of the purified radiolabelled antigen recognized by the MOv19 MAb (¹²⁵I-CaMOv19) on insolubilized MOv19. To investigate further whether the Ab2 MAb is the internal image, of CaMOv19, Id19.1 was used as immunogen with the aim to induce an anti-CaMOv19 response. The antisera tested by indirect solidphase radioimmunoassay (RIA) on the Ab2 MAb and the irrelevant isotype-matched control MAb revealed an anti-anti-idiotypic response (Ab3). However, no Ab3 antibodies with Ab1-like specificity (Ab1') were found in the immune sera, as assessed by testing the antisera both in indirect immunofluorescence (IF) and solid-phase RIA on CaMOv19-positive target cell lines.