Thymosin-dependent T-lymphocyte response in inflammatory bowel disease.

Peripheral blood "total" and "avid" thymus-dependent (T) lymphocytes were enumerated in 45 patients with Crohn's disease (CD) and in 23 patients with ulcerative patients (UC) by using the spontaneous rosette technique (ER). The in vitro effect of thymosin fraction 5, a polypeptide extract of the thymus gland, on avid ER formatin was also determined in these patients. The proportion and number of "total" ER were lower in patients with CD (P < 0.02), but not with UC, when compared with controls. More impressive differences were observed when "avid" ER were determined in patients with CD (P < 0.001) and UC (P < 0.05). Incubation with thymosin resulted in a significant increase in "avid" ER in patients with CD and UC, with no such effect observed in the controls. These results indicate that the determination of "avid" rather than "total" ER provides a more sensitive method for detecting alterations in T-cell immune competence. In addition, it is suggested that there is an increased number of circulating T-lymphocytes in CD and UC capable of responding to exogenous thymic factors. This may indicate the presence of a thymosin-responsive immunodeficiency state in these diseases.