Characteristics of the cell populations involved in extra-thymic lymphosarcoma induced in C57BL/6 mice by RadLV-Rs

The viral isolate RadLV-Rs induces in C57BL/6 mice an extra-thymic lymphosarcoma characterized by a massive enlargement of spleen and lymph nodes, which results in 100% mortality within 100 days. The spleen is the primary focus of the disease whereas lymph nodes are secondarily invaded. Simultaneously mice display a mild anaemia and an increased spleen CFU content. The enlarged organs contain an heterogeneous cell population formed of T cells, B cells and cells in which neither T nor B marker could be detected (non-T non-B cells). In spleen, T cells initially increase and afterwards decline, whereas B cells expand constantly although at a slower rate than non-T non-B cells whose number reaches 5–10 times the normal range. An almost absolute unresponsiveness of spleen and lymph node cells to Con A and PHA is observed at every stage of the disease. Response of B cells to LPS is initially normal in lymph nodes but depressed in spleen. Afterwards it drops to nil value in both organs. Although the presence of suppressive cells was demonstrated in leukaemic spleens, an intrinsic unresponsiveness of some elements cannot be ruled out. Defect (or suppression) of the T sub-population involved in B maturation was suggested by the high levels of IgM and IgG 2a and the simultaneously decreased values of IgA and IgG 1 in leukaemic mice sera. Experiments carried out with radio-chimaera restored with bone marrow differing by chromosome marker indicate that (a) cells necessary for leukaemia induction are provided by the progeny of the injected CFUs (b) very few progenitors need to be transformed to initiate the proliferative disorder. The present results indicate that the malignant proliferation belongs to the non-T non-B cell population.