Mechanisms of T cell hyperreactivity in obese strain (OS) chickens with spontaneous autoimmune thyroiditis: lack in nonspecific suppression is due to a primary adherent cell defect

The disturbed homeostasis of the immune system in Obese strain (OS) chickens with spontaneous autoimmune thyroiditis consists in a general T cell hyperreactivity (concanavalin A hyperresponsiveness, interleukin 2 (IL 2) hypersecretion), particularly expressed by those lymphocytes which infiltrate the diseased thyroid gland. This abnormality has been attributed to a defective regulation of both IL 2 production and IL 2 function by low m.w. factors, which are present in serum and splenocyte culture supernatants of normal chickens, but deficient in the OS. In the present study we identified the cellular origin of IL 2 antagonistic activity as a nonlymphoid, adherent cell. Suppressor factor production in vitro was confined to the plastic adherent fraction of spleen cells and preincubation of splenocytes with nylon wool, silica particles, or carbonyl iron significantly reduced the nonspecific suppressive activity of the culture supernatant. Kinetic studies revealed the defect in nonspecific suppression to entail prolonged IL 2 production by concanavalin A-activated OS spleen cells. In vivo treatment of normal White Leghorn chickens with silica led to a decrease in suppressive serum activity down to the OS level, whereas neither neonatal thymectomy nor bursectomy had any effect. The defective suppressor factor production in autoimmune chickens appeared to be due to a functional, but not numeric defect of macrophages as revealed by phenol red staining. The possibility that this aberration in adherent cell function might be a secondary phenomenon to the recently described reduced corticosterone tonus in OS chickens was excluded by in vivo substitution with exogenous glucocorticoids which did not normalize the suppressor defect in serum or in conditioned medium. Finally, we present evidence that T lymphoblasts from OS animals are less susceptible to IL 2 antagonistic regulation than normal cells, which possibly further contributes to the T cell hyperfunction of this autoimmune strain.