[Characteristics of distribution and quantity of dendritic cells subtypes in hyperplastic thymus in patients with myasthenia gravis]

Objective: To investigate the characteristics of the distribution and amount of different subtypes of dendritic cell (DC) in myasthenia gravis(MG). Methods: We collected the thymic specimens from 32 patients who received thymoctomy because of cardiac surgery from January 2016 to December 2016 and selected 14 of them as normal control. Meantime, 61 MG patients who combined with thymic hyperplasia and received extended thymectomy were collected and selected 8 of them as experiment group.Immunohistochemical methods were used to label the two subtype DCs: plasmacytoid dendritic cell (pDC) and classical/conventional dendritic cell (cDC), to observe the distribution of these two DC subtypes in thymus and also quantify them in different thymus structures by image analysis software.Comparing with normal thymus of the same age, we intended to demonstrate the characteristics of distribution and density of DC subtypes in patients who had MG and hyperplastic thymus. Results: (1) We labeled pDC and cDC by staining with CD123 and CD11c.The two DC subtypes distributed in both cortex and medulla, and the majority gathered in medulla, the density of pDC in thymus cortex was (34±6)/mm(2)(n=14), the density of pDC in thymus medulla was (247±35)/mm(2)(n=14), the density of cDC in thymus cortex was (21±4)/mm(2)(n=14), the density of cDC in thymus medulla was (123±16)/mm(2) (n=14). (2) The density of pDC in thymus cortex and medulla of patients with MG was lower when compared with the normal group (the density of pDC in thymus cortex, [(39±10)/mm(2) vs (29±5)/mm(2)], the density of pDC in thymus medulla, [(279±48)/mm(2) vs (236±49)/mm(2)], but with no significant difference.There was no significant difference between the density of cDC in thymus cortex of patients with MG patients and normal people, however, the amount of cDC increases in medulla and the difference was statistically significant (P<0.05). (3) The density of cDC in thymus medulla (except for germinal center) was higher than normal people (110±18) /mm(2) vs (187±29/mm(2)), though the difference was not statistically significant (P=0.059 9). The density of cDC in the ectopic germinal center (GC) of MG patients increased obviously compared with that in thymus medulla [(203±44) /mm(2) vs (439±69)/mm(2)] and the difference was statistically significant (P<0.05). Conclusions: The density of cDC increases significantly in thymus medulla of MG patients, especially gathering around or in the ectopic GC. It indicates that cDC may play an important role in the formation of ectopic GC in the hyperplasia thymus, thus involves in the disease process.