Improvement of an enzyme linked lectin assay to determine recombinant mistletoe lectin I

Extracts from Viscum album leaves, with mistletoe lectin I (ML I) as the main therapeutic agent, are commonly used as an immunomodulating adjuvat in tumour therapy. Because of its popularity against cancer and the possibility for a better standardisation a recombinant ML I (rML I) was developed by Eck et al. To improve the sensitivity of an already established enzyme linked lectin assay (ELLA) for rML I human haptoglobins with different phenotypes (1.1, 2.1 and 2.2) are used to replace asialofetuin as matrix. To determine the carbohydrate binding specificity of the tested glycoproteins the ELLA was realised in the presence of the competitive carbohydrate beta-d-lactose. It could be shown that using haptoglobin phenotype 1.1 instead of asialofetuin improved the test results markedly. Both, the limit of detection and the limit of quantitation were decreased by an order of magnitude. However, this positive result was obviously accompanied by a loss in specificity of the test. The specificity of asialofetuin for rML I is almost six-fold higher than for the tested haptoglobins. Thus, in cases where high specificity and less sensitivity values for rML I is required the ELLA should still be run with asialofetuin as binding partner.