Diminished peripheral blood monocyte DR antigen expression in systemic lupus erythematosus

We have studied DR expression on peripheral blood adherent cells, that consist of greater than 95% nonspecific esterase positive monocytes, of 50 systemic lupus erythematosus (SLE) patients. DR expression was determined using anti-DR antibody and complement mediated cytotoxicity. DR expression by SLE cells was significantly less than normal (p less than 0.001). There was no significant correlation between diminished DR expression and clinical activity or steroid treatment of the SLE patients. The DR expression on monocytes from seven patients that had elevated serum interferon levels was either in the normal range or above normal. DR expression by unstimulated SLE monocytes incubated for 3 days in vitro spontaneously decreased to 23 +/- 4% which was comparable to 31 +/- 4% for controls. The addition of interferon containing concanavalin A stimulated mononuclear cell culture supernatant (Con A sup) only partially prevented this decrease and yielded 49 +/- 7% DR+ SLE monocytes as compared with 69 +/- 6% DR+ control monocytes after 3 days of incubation (P less than 0.02). Addition of indomethacin to cells incubated with Con A sup did not significantly increase SLE monocyte DR expression, suggesting that prostaglandins did not play an important role in reducing in vitro DR expression by SLE cells. The reasons for the depressed SLE adherent cell DR expression remain unclear, as well its possible affect on immune responses. Further study of SLE monocytes may provide clues to understanding the disease.