Follicular lymphomas express B7-1 and B7-2 on the cell surface in situ. Immunoperoxidase staining of a representative small cleaved follicular center cell lymphoma using the Vectastain ABC Elite reagents. For B7-1, MoAb clone EW3.4B2.C4 was used and for B7-2 detection clone HA5.2B7. Similar staining for B7-1 and B7-2 were seen using other B7-1 or B7-2 MoAbs or CTLA4-Ig, respectively.