Piringer’s lymphadeno- pathy. Radioactive in situ hybridization for the detection of Ig heavy chain gene transcripts. (a) Igμ in situ hybridization, antisense: the vast majority of the monocytoid B cells are negative, whereas resting mantle B cells are clearly labeled. Some plasma B cells in the germinal center display extremely intensive labels. (b) Igγ in situ hybridization, antisense: most monocytoid B cells are weakly labeled, whereas mantle B cells are completely negative. Some germinal center B cells display a moderate labeling, whereas others are very intensely labeled (plasma cells). (c) Igγ in-situ hybridization, sense: negative control. No cells are labeled. MCB, monocytoid B cells; FM, follicle mantle; GC, germinal center.