In vitro thymosin effect on T lymphocytes in ankylosing spondylitis.

Peripheral blood "total" and "avid" T-cell rosettes (ER) were enumerated in 35 patients with ankylosing spondylitis (AS). The in vitro effect of thymosin fraction 5 on "avid" ER formation was also determined. "Total" ER numbers, but not proportions, were lower in patients with AS as compared to matched controls, Both the proportion and number of "avid" ER were lower in the patient group. Thymosin induced a significant increase in "avid" ER proportions and numbers in the patient group with no such effect observed in the controls. It is suggested that there are increased numbers of circulating T lymphocytes in patients with AS that can respond to exogenous thymic factors and acquire the capability to form "avid"ER.