IDENTIFICATION OF THE TUMOR-ANTIGEN 90K DOMAINS RECOGNIZED BY MONOCLONAL-ANTIBODIES SP2 AND L3 AND PREPARATION AND CHARACTERIZATION OF NOVEL ANTI-90K MONOCLONAL-ANTIBODIES

The tumor antigen 90K (Mac-2BP, L3 antigen), which has been shown to h ave T cell costimulatory activity, is a similar to 90 kDa secreted pro tein found in high levels in plasma, saliva, breast milk and other hum an fluids. The 90K antigen can be divided into three domains: an amino terminal scavenger receptor cysteine-rich (SRCR)-like domain (D1), fo llowed by a heavily glycosylated mucin-like domain (D2) and a similar to 27 kDa carboxy-terminal domain (D3). In this study we report on the construction of six different 90K immunoglobulin (Ig) fusion proteins containing different 90K domain combinations. Initially these fusion proteins were used to identify which 90K domain contains the epitopes recognized by the anti-90K monoclonal antibodies (mAb) SP2 and L3. Bot h of these mAbs were found to recognize 90K-D2. A new panel of anti-90 K mAb was then generated by immunizing mice with ascites derived 90K p rotein. The 90K domain specific fusion proteins were then used to iden tify novel anti-90K mAbs which recognize the amino terminal SRCR domai n and the carboxy terminal similar to 27 kDa domain of 90K. Two novel anti-90K SRCR (D1) and one anti-90 27 kDa domain (D3) mAbs were obtain ed. These 90K-Ig fusion proteins, as well as the novel and existing an ti-90K mAbs, provide a set of tools which will allow further dissectio n of the structure and function of this immune modulatory protein. (C) 1997 Academic Press.