Increased level of serum HLA class I antigens in patients with systemic lupus erythematosus. Correlation with disease activity

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Abstract
The level of soluble pYn‐assoriated HLA Class I heavy chains (sHLA‐I) and of soluble β2‐μ‐free HLA Class I heavy chains (sHLA‐FHC) was found to be significantly higher in sera from 58 patients with systemic lupus erythematosus (SLE) than in those from 82 age and sex‐matched controls. The level of serum sHLA‐I in patients with SLE was significantly correlated to disease activity. Western blotting analysis showed that the 44‐kDa isoform represents the major component in the antigens immuno‐precipitated by anti‐β2‐μ mAb NAMB‐1 and by anti‐β2‐μ‐free HLA Class I heavy chain mAb HC‐10 from sera of patients with SLE. These results suggest that the increased serum levels of sHLA‐I and of sHLA‐FHC in patients with SLE reflect their increased shedding from cell membrane. In view of the ability of sHLA‐I and of sHLA‐FHC to induce apoptosis of activated T cells, it is suggested that their increased serum levels in patients with SLE is triggered by dysregulation of the immune system leading to T‐cell activation. The increased serum levels of sHLA‐I and of sHLA‐FHC may be used by the immune system to control the pool of activated T cells by inducing apoptosis. If this possibility is proven to be correct, modulation of the serum level of sHLA‐I and of sHLA‐FHC may be utilized to develop strategies to treat SLE.