Impaired T cell capping and receptor regeneration in active systemic lupus erythematosus. Evidence for a disorder intrinsic to the T lymphocyte.
It is currently unclear whether the T cell dysfunctions observed during active systemic lupus erythematosus (SLE) reflect a disorder intrinsic to the T cell or defects that result from interaction with anti-T cell autoantibody. To determine whether a disorder intrinsic to the T cell exists in SLE, the T cell capping mechanism was selected as a model of cellular function. The normal T cell capping mechanism is a rapid, energy-dependent and coordinated sequence of membrane events that consists of microaggregation, capping, endocytosis, and regeneration of the surface molecule. The monoclonal antibodies OKT3, OKT4, and OKT8, directed against the T cell-specific membrane glycoproteins T-3, T-4, T-8, served as specific probes of the glycoproteins' mobility within the membrane and membrane glycoprotein regeneration. When compared with greater than 91% T cell capping in normal and control subjects with active Sjögren's syndrome, active rheumatoid arthritis and active tuberculosis, only 49-60% of T cells from active SLE patients completed the capping sequence (SLE vs. healthy controls; T-3, P less than 0.002; T-4, P less than 0.004; T-8, P less than 0.002). Colchicine (10(-5) M), which inhibits microtuble polymerization and augments the rate of normal T cell capping, failed to restore the abnormal capping. However, as judged by the elapsed time intervals to half-maximal capping, the capping kinetics of the T cells able to initiate capping were not significantly different from controls. Fluorescence microscopy demonstrated an abnormal staining pattern characterized by microaggregation of ligand-glycoprotein complexes on resting T cells, coarse aggregation of ligand-glycoprotein complexes over the surfaces of cells that failed to cap, and cleaved or disrupted caps. After clearance of determinants by capping, greater than 94% of T cells from healthy controls regenerated T-3, -4, and -8 within 24 h. In contrast, only 20-40% of capped T cells from active SLE patients reexpressed new determinants. With improving disease activity, the proportion of cells capping and regenerating T-3, -4, and -8 increased, but remained significantly below control levels. In conclusion, this study has identified a disorder of T cell surface glycoprotein mobility and regeneration affecting the majority (60-80%) of both the T-3+, T-4+, (inducer/helper), and T-3+, T-8+ (suppressor) subsets during active SLE. Although the impaired capping and reexpression improve with disease remission, a residual defect persists. The data support the concept of a disorder intrinsic to the T cell in SLE.