Thyrocytes Responding to IFN-γ Are Essential for Development of Lymphocytic Spontaneous Autoimmune Thyroiditis and Inhibition of Thyrocyte Hyperplasia

IFN-gamma promotes the development of lymphocytic spontaneous autoimmune thyroiditis (L-SAT) in NOD.H-2h4 mice and inhibits the development of thyrocyte hyperplasia and proliferation (TEC H/P). The precise mechanisms by which IFN-gamma promotes L-SAT and inhibits TEC H/P are unknown. To determine whether responsiveness of lymphocytes or thyrocytes to IFN-gamma is important for the development of these lesions, IFN-gammaR-/- mice, which develop TEC H/P similar to IFN-gamma-/- mice, were used as recipients for adoptive cell transfer. Wild-type (WT) splenocytes or bone marrow induced L-SAT and inhibited TEC H/P in IFN-gamma-/-, but not IFN-gammaR-/- recipients. IFN-gammaR-/- recipients of WT cells developed severe TEC H/P, but did not develop L-SAT, suggesting that thyrocytes responding to IFN-gamma are important for inhibition of TEC H/P. Unexpectedly, IFN-gammaR-/- splenocytes or bone marrow did not induce L-SAT in IFN-gamma-/- or WT mice even though IFN-gammaR-/- lymphocyte donors produced as much IFN-gamma as lymphocytes from WT donors, and thyrocytes could respond to IFN-gamma. Real-time PCR indicated that recipients of IFN-gammaR-/- bone marrow expressed less mRNA for IFN-gamma-inducible chemokines compared with recipients of WT bone marrow. This might limit the migration of IFN-gammaR-/- lymphocytes to thyroids. Few IFN-gammaR-/- lymphocytes infiltrated thyroids even in the presence of WT lymphocytes, suggesting that lymphocytes unable to respond to IFN-gamma are not induced to migrate to thyroids. These results suggest that thyrocytes must be able to respond to IFN-gamma for the development of L-SAT and inhibition of TEC H/P, and lymphocytes must be able to respond to IFN-gamma to induce L-SAT.