Passive transfer of antibodies to the linear epitope 60 kD Ro 273–289 induces features of Sjögren’s syndrome in naive mice (1)
Sjögren’s syndrome (SS) is an autoimmune inflammatory disease that affects the lacrimal and salivary glands causing dry eyes and mouth. Anti-Ro60 antibodies are observed in SS patients. The Ro60 273-289 (Ro274) is identified as the B-cell epitope of Ro60. In fact, anti-Ro274 antibodies were shown in SS patients. Immunization of Ro274 elicits anti-Ro274 antibodies and induces SS like illness. Passive transfer of anti-Ro274 antibodies induce suction deficit in simulated salivary flow into naive Balb/c mice, however no mononuclear cell infiltration and histological abnormality in salivary glands.
Sjögren’s syndrome (SS) is an autoimmune disease affecting the exocrine glands. Ro/SS-A (Ro60) and La/SS-B (La) of nuclear antigens are specifically targeted in systemic lupus erythematosus (SLE) and SS. In the previous studies, Ro274 (273-289), Ro413 (413-428) and Ro 480 (480-494) were found as B-cell epitopes on Ro60. The Ro274 amino acid sequence is conserved 100% between mouse and human.
Balb/c, 6-10 weeks old, were used. The mice received the immunization intraperitoneally (i.p.) with 50 ug of Ro274 peptide tagged with a terminal cysteine (LQEMPLTALLRNLGKMT) with complete Freund’s adjuvant (CFA) on day 0, followed by the same peptide with incomplete Freund’s adjuvant (IFA) on day 14, 35, 51, and 63.
NOTE: Is there sex-bias in the model?
The serum was collected and the total IgG was purified by Protein G affinity column. The Ro274 specific antibodies were purified using a Ro274 multiple antigenic peptide (MAP) coupled cyanogen bromide activated sepharose column.
Naive mice received 100 ug of total IgG or anti-Ro274 antibodies by IP injection. Saliva volumes were evaluated on day 0 and day 4 after the antibody transfer.
The Ro274 peptide immunized mice developed anti-Ro274 antibodies on day 16.
Adaptive transfer of anti-Ro274 antibodies deposited on salivary glands but histologically normal. However, these mice showed significantly lower salivary flow in mice on day 4, suggesting the salivary glands have lower function by the anti-Ro274 antibodies
Many SS patients with severely dry mouths have histologically normal salivary glands, indicating the salivary glands are not destroyed but simply not functioning. The results may be correlated with the human patients. The salivary dysfunction can be restored by washing out deposited IgG in the adaptive transfer animal models. In addition, the antibodies may penetrate into live cells by endocytosis using Fc receptors on plasma membranes, resulting in binding antibodies with Ro60 in the nuclear fraction of cells. Antibodies can also get into cells without the Fc receptor.
Ribosomal phosphoprotein P0 antigen present on the cell surface may contribute to the translocation. These binding induced dysfunction of cells in the salivary glands.
Since, inflammatory cytokines such as tumour necrosis factor (TNF)-α and interferon (IFN)-γ can upregulate Ro60 and its translocation to the cell membrane, lipopolysaccharide injection may assist to develop the salivary gland dysfunction with the anti-Ro274 antibody transfer.