Absorption of IgG does not enhance toxoplasma IgM and IgA immunoblotting

This study evaluated whether removing IgG from serum samples improves the detection of Toxoplasma-specific IgM and IgA antibodies using immunoblotting. Researchers tested 10 serum samples before and after IgG absorption using Protein G-Sepharose 4. While IgG levels were reduced by an average of 96%, IgM and IgA levels were also significantly reduced by 53-56% on average. The reduction occurred regardless of whether Protein G-coated or uncoated Sepharose was used, suggesting dilution rather than specific binding was responsible. Although IgG immunoblotting became negative after absorption, IgM and IgA immunoblotting patterns were either unaffected or showed fewer and weaker bands. Testing absorbed samples at higher concentrations did not improve detection. The authors concluded that IgG pre-treatment provides no benefit for Toxoplasma IgM and IgA immunoblotting and actually reduces rather than enhances sensitivity, contrasting with findings from viral pathogens.

Key findings

• IgG absorption reduced IgG levels by 96% on average but also decreased IgM and IgA levels by 53-56%, likely due to sample dilution rather than specific antibody binding.
• Complete removal of IgG (>90% reduction) did not enhance IgM or IgA immunoblotting sensitivity; instead, absorbed samples showed fewer and weaker bands in some cases.
• IgA immunoblotting patterns were completely unaffected by IgG absorption across all tested samples.
• Protein G-Sepharose 4 and uncoated Sepharose 4 produced similar reductions in IgM and IgA levels, indicating Protein G does not specifically bind these antibodies.
• Pre-treatment of sera to remove IgG provides no benefit and may reduce sensitivity for Toxoplasma IgM and IgA detection by immunoblotting.