Hepatitis virus B e antigen subtypes HBeAg/1 and HBeAg/2 can be distinguished by a micro-Ouchterlony immunodiffusion assay and a solid-phase radioimmunoassay using serum IgG-associated HBeAgs and liver- and serum-derived IgG-free HBeAgs. The liver- and serum-derived HBeAg consisted of two different antigenicities, HBeAg/1 and HBeAg/2. Both the liver-derived HBeAg/1 and HBeAg/2 had mol. wt. of 30000 (monomer) and 90000 (trimer) and shared the same isoelectric point of 4.3 to 4.8. Approximately 80% of liver-derived HBeAg (mol. wt. 30000 and 90000) had HBeAg/1 activity and the remaining 20% was HBeAg/2. The serum-derived HBeAg/1 and HBeAg/2 were both associated with IgG to form heterogeneous moieties with apparent mol. wt. of 240000, 400000 and 540000 or were free, with mol. wt. 30000 (monomer) and 90000 (trimer). The serum HBeAg of mol. wt. 90000 was further differentiated into two molecular species, one trimer and the other associated with albumin. Large types of both HBeAg/1 and HBeAg/2 were recovered by isoelectrictric focusing at pH 5.5 to 7.5 (mol. wt. 240000), 5.7 to 8.0 (mol. wt. 400000) and 6.4 to 8.4 (mol. wt. 540000) respectively, while small types of both exhibited a narrower range of isoelectric points similar to liver-derived antigens. In most sera, antigenicity of half of the serum IgG-associated HBeAg was HBeAg/1 and the remaining 50% was HBeAg/2, whereas 80% of the free HBeAg had HBeAg/1 activity and the remaining 20% was HBeAg/2. These results indicate that HBeAg/1 and HBeAg/2, although antigenically distinct, are very similar physicochemically with respect to both mol. wt. and isoelectric point. Dissociation of the ‘large’ HBeAg/1 and HBeAg/2 moieties into three mol. wt. species (160000, 32000 and 16000) was achieved by 6--guanidine-HCl treatment followed by gel filtration through Sepharose 6B. The 160000 species was IgG, having both anti-HBeAg/1 and anti-HBeAg/2 activities. In addition, the lower mol. wt. polypeptides (32000 and 16000) exhibited both HBeAg/1 and HBeAg/2 activities. Therefore, we suggest that the IgG associated with the HBeAg molecule forms a true immune complex rather than a non-specific association between HBeAg and IgG. Furthermore, the 32000 mol. wt. polypeptide split into two species of 16000 mol. wt. when heated at 100 °C for 2 min. On the basis of these results, the 16000 mol. wt. polypeptide may be assumed to be the essential polypeptide bearing HBeAg/1 and HBeAg/2 activities in the liver and serum.


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