Single-cell isolation of one HRS cell from a frozen section of a lymph node involved by HD and immunostained with CD30/HSR4 MoAb. (A) Tissue section before single-cell picking: HRS cell is strongly positive with the anti-CD30 antibody, whereas the surrounding lymphocytes are negative. (B) Tissue section after the micromanipulation of the nucleus of HRS cell (APAAP technique with nuclear counterstaining; original magnification × 400).