Protein Signature of LMP1 Signaling in PTLDs Identifies and Mimics Inter/Perifollicular CD30+ EBV− B Blasts.

EBV-associated B-cell Post-Transpant Lymphoproliferative Disorders (PTLDs) represent a diverse group of lesions morphologically, in clinical presentation and behaviour, ranging from early reversible lesions to monomorphic aggressive lymphomas.

Polymorphic cases, which represent the focus of our analysis, contain a mixture of cells in various EBV latency stages, defined by EBNA1, EBNA2 and LMP1 immunostaining.

LMP1 is a key viral protein for cellular transformation and, analogously to CD40, engages TNF Receptor Associated Proteins and activates NF-kB and NF-kB-responsive genes.

We analyzed the protein signature of LMP1 in PTLDs and non-PTLD tonsils by double staining for LMP1, CD30, CD20, Pax5 and signaling molecules. A remarkably conserved set of proteins, associated with LMP1/CD40 signaling and NF-kB activation is expressed both in the EBV-infected lymphoid population in polymorphic PTLDs and in a normal B-cell subset(s) in reactive tonsils. These proteins include highly expressed CD30, JunB, nuclear cRel, TRAF-1, Bcl-XL, MUM1, CCL22 and downregulated BCL6 and CD10.

We observed that EBV infection, possibly through LMP1 and LMP2A signaling, results in varioius degrees of differentiation within the neoplastic clone. EBER+ terminally differentiated mucosa-associated IRTA-1+ marginal zone B-cells and CD138+ plasma cells were identified in most cases, including control post-transplant tonsils with no overt disease. We document for the first time in situ, in-vivo evidence of EBV latently infected post-Germinal Center B cells of marginal and plasma cell types in PTLDs. Polymorphic PTLD cases represent EBV-induced expansion of B cells, mimicking CD40L-like activated Peri/Interfollicular CD30+ normal B-cells.