Introduction
Thymoma is the most common anterior mediastinal mass in adult[1]. About 30% of patients with thymoma have MG (thymomatous MG) [2]. Almost all patients with thymomatous MG have antibodies to ACHR [3]. However, the pathogenesis of thymomatous MG and the signal path of antibodies generation are not entirely clear. Studies reveal that TFH cells play a fundamental role in humoral immunity deriving from their ability to provide help for germinal center (GC) formation, B cell differentiation into plasma cells and memory cells, and antibody production in secondary lymphoid tissues [4]. Furthermore, Lieping Chen and his colleagues found that PD-1 expression on T cells and PD-L2 expression on B cells controlled TFH and PC numbers. PD-1 regulates germinal center B cell survival and the formation and affinity of long-lived plasma cell[5].
What’s more, thymic TFH cells might involve in the pathogenesis of MG with thymoma [6,7].
PD-1 is highly expressed in TFH. The roles of PD-1/PD-L1,2 signaling in the pathogenesis of thymomatous MG has been virtually unstudied. However, numerous studies showed that PD-L1 protein expression was not associates with the status of MG [8,9]. In that case, PD-L2 may be an alternative and valuable marker. Previous studies shown that PD-L2 was expressed on solid tumor, APC (Regulation of PD‐1, PD‐L1, and PD‐L2 expression during normal and autoimmune responses) and medullary thymic epithelial cells[10] with high expression in some organs ( like lung, liver and heart) and low expression in some others (like spleen, lymph node and thymus. And there is a growing relationship between PD-1/PD-Ls and autoimmune disease[11]. So, we have a guess that PD-L2 may play an important role in the status of MG in patients with thymoma.
The purposes of this retrospective study were to characterize the association between the expression of PD-L2 in thymoma and the clinicopathologic features of the patients and to evaluate the relationship of PD-L2 expression and the status of MG.