Molecular aspects of systemic lupus erythematosus: murine endogenous retroviral expression.

Systemic lupus erythematosus is an immune-mediated disease in which the etiology is unknown. Full-length (8.4 kb), type C, modified polytropic (Mpmv) retroviral transcripts from the thymus are characteristic of murine lupus. Reciprocal bone marrow transplantation studies determined that this thymic expression maps to the pre-T bone marrow stem cell. In vitro and in vivo oligonucleotide antisense work suggest that type C retroviruses play a role in immune activation. This paper summarizes our studies of endogenous retroviruses in murine lupus.

Studies of T cell deletion and T cell anergy following in vivo administration of SEB to normal and lupus-prone mice.

This study examines the responses of lupus-prone NZB, (NZB x NZW) F1, BXSB, MRL-lpr/lpr and control mice (H-2 and Mls matched) to in vivo administration of the superantigen staphylococcal enterotoxin B (SEB). Two weeks after i.v. administration of 500 micrograms SEB, CD4+V beta 8+ lymph node T cells were deleted equivalently by lupus-prone and control mice. However, IE+ strains deleted a greater proportion (47% to 77%) of their CD4+V beta 8+ cells than did IE- strains (24% to 27%). CD8+V beta 8+ cells were deleted less than CD4+V beta 8+ cells by injection of 500 micrograms SEB. IE- strains failed to delete CD8+V beta 8+ cells, whereas six of seven IE+ strains deleted > 25% of their CD8+V beta 8+ cells. IE+ MRL-lpr/lpr mice showed some impairment in deletion: they failed to delete CD8+V beta 8+ cells at all doses of SEB and had reduced deletion of CD4+V beta 8+ cells at low doses of in vivo SEB (10 and 50 micrograms). Peripheral expansion of the intrathymically deleted V beta 7 TCR family was not observed in lupus-prone mice 2 wk after 500 micrograms in vivo SEB. In vitro restimulation with SEB of mice previously injected with 500 micrograms SEB demonstrated anergy in T cells from all strains, including the IE- and MRL-lpr/lpr. This result contrasts with previous reports of tolerance defects in lupus-prone strains using B cell read-out assays as measures of tolerance. The present study demonstrates that there is no global defect in peripheral T cell deletion or anergy in lupus-prone mice to the superantigen SEB. Although additional Ag would need to be studied, these experiments raise the possibility that some reported tolerance defects in lupus-prone strains may reflect excessive B cell responses to relatively normal T cell signals.

Role of endogenous retroviruses in autoimmune diseases.

Retroviruses have been implicated in the pathogenesis of murine and human lupus; however, many positive findings have been followed by alternative explanations. Initial findings implicating xenotropic retroviruses were subsequently invalidated. The first solid demonstration that endogenous retroviruses mediate disease was the study of SL/Ni mice. Here budding ecotropic retroviral particles from arterial smooth muscle cells caused an antibody response to the particles with subsequent complement deposition. Our laboratory has focused on derangements in endogenous MCF retroviral expression. We found that lupus-prone NZB, BXSB and MRL strains have a marked increase in expression of Mpmv RNA in their thymuses while bone marrow expression did not differ from normal strains. Sequence analysis demonstrated mutations in the NZB endogenous retroviruses which could alter expression. A phosphorothioate antisense oligonucleotide to the initiation sequence of Mpmv caused lymphocyte activation in vivo in normal mice, providing further evidence for in vivo effects of Mpmv and potential for pathological abnormalities in lupus-prone strains.

Uptake of oligodeoxyribonucleotides by lymphoid cells is heterogeneous and inducible.

Oligonucleotide uptake was studied in cultured murine spleen and lymph node cells using internally radiolabeled and fluorescein-5-isothiocyanate (FITC)-labeled oligonucleotides. Lymphoid subpopulations were distinguished by flow cytometry and staining with antibodies to cell-surface molecules. Approximately 5% of fresh lymphoid cells take up substantial amounts of oligonucleotide. The percentage of B cells that take up oligonucleotide increased fivefold if cells were cultured for at least 24 hr prior to incubation with labeled oligonucleotides, and increased 10-fold if cells were precultured for 48 hr. T-cell uptake changed very little in culture. Cultured CD4+ and CD8+ T cells had similar oligonucleotide uptake that was less than one-third of that in cultured B cells, but CD4-CD8- T cells had a higher percentage of cells taking up oligonucleotide than did B cells. T- or B-cell mitogens caused markedly increased oligonucleotide uptake in T or B cells, respectively. Oligonucleotide uptake could be inhibited only partially with competitor DNA. To distinguish between cell membrane-bound and intracellular oligonucleotide, cells were washed in acid glycine buffer (which removes most surface oligonucleotide). This demonstrated that most of the oligonucleotide was intracellular. We conclude that oligonucleotide uptake is quite heterogeneous among cultured cells, and that this uptake is inducible by mitogens. These data may be important for the design and interpretation of in vitro experiments, and for the planning of in vivo therapy with antisense oligonucleotides.