GBP tends to exist in oligomeric forms. A, crude plasma and purified GBP were separated by SDS-PAGE with or without reducing agent. Immunoblotting (IB) was performed with anti-GBP antibody. R, reducing condition; NR, nonreducing condition. B, matrix-assisted laser desorption ionization time-of-flight spectra identified the purified 52, 26, and 18 kDa protein bands as the dimer, monomer, and N-terminal fragment of GBP, respectively.