13 using lymph node biopsies from four untreated patients newly diagnosed with classical nodular sclerosis hd a benign reactive lymph node biopsy was used as a control for in situ hybridization paraffin sections were mounted and fixed according to standard protocols a human cdna probe specific for il 13 was generated by pcr using rt pcr and il 13 specific primers set out in seq id nos 1 and 2 pcr was carried out using standard conditions well known and routinely practiced in the art the 388 bp amplification product was cloned into the pcrii vector ta cloning kit invitrogen carlsbad calif usa sense and antisense probes were synthesized from the linearized vector with sp6 or t7 polymerase labeled with 32 p utp and processed as previously described hui el al nat genet 3 241 246 1993 the sections were counterstained with toluidine blue using a standard protocol the results confirmed strong and specific il 13 expression by morphologically identifiable h rs cells in all patients in contrast to background levels of il 13 expression in non h rs cells and cells from the control biopsy to investigate the effects of il 13 and il 5 on the proliferation of h rs cells l428 kmh2 and hdlm2 cells were incubated with either i medium alone ii medium containing neutralizing antibodies to il 13 or il 5 or ii isotype matched control antibodies proliferation was measured by determining 3 h thyridine incorporation at 24 48 or 72 hours after treatment hd derived l428.