INFLUENCE OF THE LPR ENVIRONMENT ON THE LYMPH-NODE CELL PHENOTYPES INC57BL 6 NUBG AND NULPR CHIMERAS/

Mice homozygous for the lpr gene show a marked lymphoproliferative syn drome. Most T cells which accumulate in their lymphoid organs belong t o a fairly unusual subpopulation. Although being CD44(+) T cells expre ssing neither CD4 nor CD8, they are CD3 T-cell receptor (TCR) crp posi tive and express both Thy-1 and B220, the B-cell form of the CD45 mark er. To support engraftment and development of transferred lpr lymphomy eloid cells, athymic recipients must be genetically lpr. While nude/be ige (nubg) recipients do not allow the development of any lymphoprolif erative syndrome, this is variable in nude/lpr (nulpr) recipients, and the genotypic origin of the proliferating lymphocytes in nulpr recipi ents is unclear. In this study, the surface phenotype of lymph node ce lls from nulpr recipients of lpr grafts ([lpr --> nulpr] chimeras) was analysed by flow cytometry, and compared with various chimeras and pa rental (donor and recipient) strains as controls. Abnormal cells of th e lpr type were not detectable either in [lpr --> nubg] chimeras or in [wild --> nubg] controls. Absence of lpr cells was also seen in neona tal Ipl thymus-grafted nubg mice engrafted previously with lpr haemato poietic cells. In contrast, a substantial emergence of double-positive B220(+) Thy-1(+) + cells occurred in [lpr --> nulpr] chimeras, togeth er with high levels of CD4(+) cells, a substantial fraction of which m ight express B220. Finally, in thymus-grafted nulpr mice, the levels o f B220(+) Thy-1(+) cells were as high as in lpr mice and there was aga in an expansion of CD4(+) (potentially B220(+)) cells. Abnormality of the nulpr haemopoietic environment was also shown by the low percentag es of T cells, particularly CD8 + cells, in short-lived [wild --> nulp r] chimeras. Taken together, our results underline the differences bet ween the nubg and nulpr environments.