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.