Purification and refolding of recombinant porcine β 2 m proteins Porcine β 2 m was purified in the same way as human β 2 m (Ostergaard et al. 2001; Ferre et al. 2003) . Briefly, the ureadissolved β 2 m protein was purified by Ni 2 +/IDA metal chelating affinity column chromatography, refolded by drop-wise dilution into an excess refolding buffer under stirring (25 mM Tris, 300 mM urea, pH 8.00), and then concentrated (VivaFlow, 10 kDa). The refolded product was purified by Ni 2 +/IDA metal chelating affinity column chromatography again (this time in aqueous buffer, i.e., without urea). Fractions containing HAT-pβ 2 m were iden-tified by SDS-PAGE and pooled. Removal of the HAT tag was performed by cleavage with factor Xa restriction protease (FXa) followed by renewed purified by Ni 2 +/ IDA metal chelating affinity and Superdex200 gel filtration column chromatography, concentrated by spin ultrafiltration (10 kDa), mixed 1:1 with glycerol, and stored at −20°C.