Increase in peripheral large granular lymphocytes in postpartum autoimmune thyroiditis

In order to elucidate the mechanism of postpartum aggravation of autoimmune thyroid disease (AITD), we serially examined the change in the proportion of peripheral large granular lymphocytes (LGL), which have activities of NK, K and/or cytotoxic T cells, in their postpartum period. Within 6 months postpartum, the percentage of LGL increased transiently in patients with AITD who remained euthyroid, or developed destructive thyrotoxicosis and/or hypothyroidism due to thyroiditis and even in normal controls. These changes in the LGL percentage were more obvious in the patients who had marked postpartum thyroid dysfunction. In contrast, we did not find a definite increase in the LGL percentage within 6 months postpartum in patients with Graves' disease who relapsed into Graves' thyrotoxicosis. These deta suggest that the increase in LGL in the postpartum period may be related to the induction of postpartum destructive thyrotoxicosis and/or hypothyroidism in AITD.