After terminal bleeding and fusion of splenocytes to Sp2/0 myeloma cells, individual hybridoma cells were selected by limit dilution, and the presence of antibodies recognizing P2X4 in the supernatant was tested by immunocytochemistry on CHO cells transiently transfected with either human or mouse P2X4-Y378F. The gene discussed is P2RX4; the disease is plasma cell myeloma.