The target of antibody responses is bovine apoB. (A) 3E8.1 binding to BW cells (thick solid lines) is blocked with antimouse LDL receptor antibody and heparin (dotted lines) but the binding of H-2Kk antibody is not blocked. (B) Sera from mice, adult cows, and human donors were immunoprecipitated by 3E8.1 or isotype-matched control. Human serum was immunoprecipitated by antihuman apoB antibody (bottom, right). “C” refers to immunoprecipitation using isotype matched control antibody and “3” to immunoprecipitation with 3E8.1 mAb. (C) BW cells cultured with 10% FCS (dark solid line) or 10% lipoprotein deficient (LD) medium (dotted line) were stained with indicated antibodies. Isotype-matched antibody (thin solid line) and normal rabbit Ig (dashed line) are negative controls. (D) BW cells incubated for 1 hour in PBS containing various concentrations of FCS were stained with indicated reagents.