The phentypic changes of stromal cells in NPs with or without eLTs
The production of CXCL13 by nasal stromal cells in NPs without eLTs may point a role of stromal cells in the recruitment of B cells and initiation of eLT development. We then compared the CXCL13 expression in stromal cells from different types of sinonasal tissues. We found that compared to those in control tissues, CXCL13 mRNA expression was increased in stromal cells purfied from both NPs with and without eLTs, although a more prominent upreglation was noted in NPs with eLTs than those without eLTs (Fig 2, A).
Based on CD31 and podoplanin (Pdpn, also known as gp38) expression,29, 30 CD45 and epithelial cell adhesion molecule double negative stromal cells are classified into four subpopulations including CD31+Pdpn-blood endothelial cell (BEC), CD31-Pdpn+ fibroblastic reticular cell (FRC), CD31+Pdpn+ lymphoid endothelial cell (LEC), and CD31-Pdpn- double negative cell (DN) (Fig 2, B), which have different functions. We studied whether specific stromal cell types are involved in eLT formation in NPs. We discovered that the frequencies of FRCs were increased in both NPs with and without eLTs, and the frequencies of LECs were only increased in NPs with eLTs compared with those in control tissues (Fig 2, C and D). In contrast, the frequencies of DNs were reduced in NPs with eLTs and no significant change of BECs was found in NPs in comparison to those in control tissues (Fig 2, C and D).
Analyzing CXCL13 expression in different nasal stromal cell types, we found that CXCL13 expression was enhanced in FRCs and LECs in both types of NPs in comparision to control tissues, with NPs with eLTs having a higher upregulation than NPs without eLTs (Fig E1, A and B). CXCL13 expression in DNs was only upregulated in NPs with eLTs and no upregulation of CXCL13 was found in BECs in NPs (Fig E1, A and B). We determined the contribution of different types of stromal cells to CXCL13 expression and found that FRCs were the major source of stromal cell dervied CXCL13 in NPs (Fig 2, E and F).