Isolation of bovine follicular dendritic cells allows the demonstration ofa particular cellular prion protein

As interaction of cellular prion protein (PrPc) and the infectious agent (P rPres) appears to be a crucial pathogenic step promoted by homology, variat ion in PrPc isoforms on bovine immune cells may explain the absence of infe ctivity in most bovine lymph organs. In this study, we examined PrPc expres sion in bovine lymph organs (tonsils and lymph nodes) and on isolated folli cular dendritic cells (FDCs). We used a panel of different monoclonal antib odies (MoAbs) raised against different epitopes of prion protein. Two MoAbs recognise amino acids 79-92 (SAF 34 and SAF 32 MoAbs); the 6H4 antibody re acts with a specific peptide comprising the 144-152 amino acids, and the 12 F10 MoAb recognises the sequence 142-160. After immunolabelling of frozen s ections of lymph organs with 6H4 or 12F10 MoAbs, we detected cellular prion protein in germinal centres. However, using the SAF 34 or SAF 32 antibodie s, PrPc was revealed outside the lymphoid tissues. No PrPc was observed in the germinal centres. Therefore, we adapted the method of FDC isolation, ma king it suitable for the study of PrPc expression on their surface. Using e lectron microscopy, the presence of PrPc on the surface of FDCs was demonst rated only with 6H4 MoAb. These results suggest that bovine follicular dend ritic cells express a particular form of prion protein. Either the N-termin al part of PrPc is cleaved or the accessibility of the specific epitope (79 -92) of SAF 34 MoAb is abolished by interaction with other molecules. This particular isoform of PrPc on bovine FDCs might be related to the apparent absence of infectivity in lymph organs in cattle affected by bovine spongif orm encephalopathy.