In vitro effect of thymosin on T-lymphocyte rosette formation in rheumatic diseases.

The in vitro effect of calf thymosin fraction 5 on T-rosette forming cells (E-RFC) was studied in Sjögren's syndrome (SS), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE). The baseline percent E-RFC in sixteen normal controls was67-2 +/- 6-9. E-RFC was significantly decreased in SLE (42-6 +/- 17-0, P less than 0-0001) and SS (51-8 +/- 16-9, P less than 0-002) but not in RA (59-7 +/- 14-1). Ten of twenty-five SS patients and two of eleven RA patients had less than 50% E-RFC, and all showed a significant increase after incubation with thymosin (+ 16-5 +/- 6-5%, P less than 0-0001, and + 11 +/- 4-9%, P less than 0-001, respectively). Eleven of sixteen SLE patients had less than 50% E-RFC. Their response to thymosin was less dramatic but still statistically significant (+ 5-3 +/- 6-0%, P = 0-03). There was no response to thymosin in control subjects or in patients with baseline E-RFC greater than 50%. No increase in E-RFC was seen after incubation with calf spleen fraction 5 or known stimulators of cyclic-AMP. Sera from four active SLE patients, as well as the supernatant obtained from overnight culture of the lymphocytes from one SLE patients, were able to block T-rosette formation by normal lymphocytes, even after exposure to thymosin. Two 'blocking' sera were fractionated by sucrose density gradient ultracentrifucation. In one, the blocking capacity was found to reside in the 19S region containing IgM. In the second, the blocking capacity was in the 7S region containing IgG. Four 'blocking' lupus sera were depleted of IgG or IgM by immunoabsorption with goat anti-human IgG or goat anti-human IgM sepharose 4B. The blocking ability in three sera was partially decreased by depletion of either IgG or IgM, and in a fourth, only by removing IgG. The percent of lymphocytes staining with fluorescein labelled goat anti-human immunoglobulin antisera was increased in SLE patients (35-9 +/- 20-2 vs 21-7 +/- 5-9 in controls, P = 0-02). After overnight culture, the percent of staining cells decreased to normal values. These results suggest that thymosin can stimulate the differentiation of T-lymphocytes in patients with SS, SLE, and RA when the baseline E-RFC is decreased. Furthermore, the decreased percent E-RFC in SLE is probably due to cell-bound anti-lymphocyte antibodies that block sheep erythrocyte receptors on the T-cell and, possibly, thymosin receptors on undifferentiated lymphocytes.