Background In a previous study we demonstrated that serum autoantibodies from patients with Systemic Lupus Erythematosus (SLE) were able to induce autophagy in peripheral lymphocytes . Moreover, it is firmly established that a population of serum autoantibodies from patients with SLE can react with lymphocyte membrane proteins. Rho GDP-dissociation inhibitor β or D4-GDI, is a Rho guanosine diphosphate (GDP) dissociation inhibitor which, by binding to Rho, a small GTP-binding protein, can inhibits its dissociation from GDP. It has been demonstrated that D4-GDI controls Rho GTPase cellular distribution and interactions during cell processes, including cell polarity, cytoskeletal organization, and transduction of signals from the extracellular environment. Interestingly, D4-GDI was shown to be preferentially expressed in hematopoietic tissues, predominantly in B and T cells, and involved in lymphocyte activation, survival, and responsiveness .
Objectives We aimed to identify, in SLE patients, the specific target of autoantibodies able to react with lymphocyte surface, and to evaluate their role in perturbing autophagy.
Methods Flow cytometry analysis was performed on non-permeabilized T lymphocytes in order to demonstrate whether purified IgG from SLE patients might specifically react with the lymphocyte surface. Aiming to identify the antigenic target of these autoantibodies, an immunoproteomic analysis on cell-surface membrane proteins and mass spectrometry (MS) analysis were used. After cDNA cloning in an expression vector, the recombinant protein, corresponding to the spot identified by MS, was expressed, purified, and then used as antigen in ELISA. Fifty-two consecutive patients with SLE (F/M 50/2; mean age 39.2 years; mean disease duration 11 years), attending the Lupus Clinic of “Sapienza” University of Rome, were enrolled in this study and their sera were analyzed for the presence of specific autoantibodies. Finally, we studied if these autoantibodies were able to modulate autophagy in T lymphocytes from healthy donors by measuring the autophagy marker microtubule-associated protein 1 light chain 3 (LC3)-II in Western blot.
Results Purified IgG from sera of patients with SLE bind the lymphocyte surface and immunoproteomic analysis showed one strongly reactive spot that was identified as D4-GDI by MS. Anti-D4-GDI antibodies were detected in 24 out of 52 sera analyzed (46%). In vitro study of their effects on lymphocytes suggest that these autoantibodies are able to induce autophagy in cells from healthy donors.
Conclusions We identified a subgroup of autoantibodies reactive to lymphocyte surface as directed against D4-GDI. Studies on their effects in lymphocytes prompt us to consider these autoantibodies as potential modulators of autophagy.
Alessandri C, Barbati C, Vacirca D, Piscopo P, Confaloni A, Sanchez M, et al. T lymphocytes from patients with systemic lupus erythematosus are resistant to induction of autophagy. FASEB J. 2012;26(11):4722-32.
Scherle P, Behrens T, Staudt LM. Ly-GDI, a GDP-dissociation inhibitor of the RhoA GTP-binding protein, is expressed preferentially in lymphocytes. Proc Natl Acad Sci U S A 1993;90:7568–72.
Disclosure of Interest None Declared
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