Background/Purpose:

The interplay between effector and regulatory T cells (Tregs) is a key element among peripheral tolerance mechanisms in Systemic Lupus Erythematosus (SLE). Resistance to suppression has been acknowledged as part of the defects shown by lupus T cells. The E3 ligase Cbl-b has been shown to modulate T cell unresponsiveness in SLE. However its role in peripheral Tregs tolerance has not been addressed. The aim of this study was to assess Cbl-b expression and its relationship to the resistance to suppression phenotype, as well as the ubiquitination profile in SLE.

Methods:

We included 30 SLE patients (20 with active disease and 10 with clinical remission) and 30 age and gender matched healthy controls. Peripheral blood mononuclear cells were isolated by density-gradient sedimentation. Effector (CD4⁺CD25^–) and Tregs (CD4⁺CD25⁺CD127^–) were purified by magnetic selection. The expression of Cbl-b and the ubiquitination profile were analyzed by western blot. Proliferative responses were assessed in allogeneic and autologous cocultures by CFSE method. Differences were assessed by t Student test. p<0.05 was considered as statistically significant.

Results:

We found decreased Cbl-b expression in Tregs from SLE patients in comparison to healthy controls (1.1±0.9 vs 2.5±1.8+6, p=0.003), which was associated with resistance to suppression in proliferation assays (r=0.633, p=0.039). This phenomenon was related to a differential polyubiquitination profile characterized by deficient expression of Lys63 (K63) substrates in regulatory T cells from SLE patients when compared to healthy controls. We analyzed different signaling molecules that are prone to K63 regulation and found increased expression of phosphorylated STAT3 (pSTAT3) in T cells from SLE patients in comparison to healthy controls.

Conclusion:  Our data suggest that Cbl-b is able to regulate the interplay between effector and Tregs, particularly, the resistance to suppression by regulating the K63 polyubiquitination profile in T cells from SLE patients. Moreover, deficient K63 polyubiquitination mainly of STAT3 is associated to the enhanced pSTAT3 expression and might play a role in the maintenance of resistance to suppression in SLE, as has been previously reported for other autoimmune diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/lys63-polyubiquitination-by-the-e3-ligase-casitas-b-lineage-lymphoma-b-modulates-peripheral-regulatory-t-cell-tolerance-in-patients-with-systemic-lupus-erythematosus/