In adaptive immunity, CLEC-2+ dendritic cells (DCs) contact fibroblastic reticular cells (FRCs) inhibiting podoplanin-dependent actomyosin contractility, permitting FRC spreading and lymph node (LN) expansion. The molecular mechanisms controlling LN remodelling are incompletely understood. We asked how podoplanin is regulated on FRCs in the early phase of LN expansion, and which other proteins are required for the FRC response to DCs. We find that podoplanin and its partner proteins CD44 and CD9 are differentially expressed by specific LN stromal populations in vivo, and their expression in FRCs is coregulated by CLEC-2. Both CD44 and CD9 suppress podoplanin-dependent contractility. We find that beyond contractility, podoplanin is required for FRC polarity and alignment. Independently of podoplanin, CD44 and CD9 affect FRC-FRC interactions. Further, our data show that remodelling of the FRC cytoskeleton in response to DCs is a two-step process requiring podoplanin partner proteins CD44 and CD9. Firstly, CLEC-2/podoplanin-binding inhibits FRC contractility, and secondly FRCs form protrusions and spread which requires both CD44 and CD9. Together, we show a multi-faceted FRC response to DCs, which requires CD44 and CD9 in addition to podoplanin.
Fibroblastic reticular cell tumour in axilla- A rare entity