Supressor monocytes in patients with systemic lupus erythematosus. Evidence of suppressor activity associated with a cell-free soluble product of monocytes.

Abnormal SLE mononuclear cell responses to PHA can be corrected by removal of adherent mononuclear cells. The present study demonstrates that cell-free supernatants from allogeneic adherent cell cultures inhibit lymphocyte response and that addition of indomethacin to cultures partly blocks the inhibitory effect of the resulting supernatant. Supernatants from SLE monocyte cultures suppressed allogeneic normal T cell responses by 36% (response in supernatant 33,515 +/- 3814 cpm, media control 51,947 +/- 3173 cpm) but normal monocyte culture supernatants did not suppress (48,384 +/- 4172 vs. 47,477 +/- 3221 cpm). Early (less than 24 hr) addition of indomethacin to monocyte cultures prevented elaboration of inhibitory material. In normals, indomethacin-treated supernatants were strikingly stimulatory (response 178% +/- 24 of control), whereas similarly treated supernatants of SLE monocyte cultures were not stimulatory (response 103% +/- 8 of control). The data indicate that a soluble inhibitor of lymphocyte blastogenesis is produced by SLE monocytes.