Separation method of IgG fragments using protein L.

Protein L (IgG kappa-chain-binding bacterial protein) showed a precipitate line(pseudo-immuno-reaction) with IgG and F(ab')2 fragment, but did not show any line with the Fab fragment, the Fc fragment and free kappa-chains in the micro-Ouchterlony method. The IgG and Fab fraction obtained from pa-pain-digested IgG (from the sera of patients with chronic thyroiditis), followed by Protein A-Sepharose, were separated by Protein L-Sepharose affinity chromatography. The unbound fraction (UF) consisted of IgG(lambda) or Fab(lambda) and the bound fraction (BF) consisted of IgG(kappa) or Fab(kappa) were obtained. Anti-thyroglobulin and anti-thyroid peroxidase antibody activities were found equally in both the UF and the BF. When Fab(kappa) was reduced with dithiothreitol (DTT), the Fd fragment in the UF could be separated from the free kappa-chain and the unreduced Fab(kappa) in the BF with a Protein L-Sepharose column. A separation method of human IgG fragments such as free kappa-chain, combined forms of kappa-chain [Fab or F(ab')2], and the Fd region, using Protein L, is described.