Complement activating agents in allergenic extracts

Extracts of environmental allergens, moulds and plant pollens are known to consume haemolytic complement (huC) in human serum in vitro through the antibody-independent engagement of the first component C1 of the classical pathway. The present work was undertaken to establish the nature and characteristics of the complement activating agents in allergenic extracts and to probe their relationship with the IgE-binding allergens.

A large series of different > 10 kDa allergenic products was investigated for their capacity to consume haemolytic complement in the sera of allergic patients with specific anti-allergen IgE antibodies, as well as in normal control sera. UV-spectroscopy was used for categorizing the non-protein components in the extracts.

The experiments confirmed that huC is consumed in an antibody-independent fashion and in a qualitatively similar, but quantitatively distinct manner. The ratio of the complement activating potencies among the different allergenic preparations thereby remained constant and independent of the serum source, while an overt relationship with specific IgE-antibodies could not be established. UV-spectroscopy of the allergenic preparations revealed the presence of chemical decomposition products in nearly every extract and roughly in proportion to the complement activating potencies.

The data support the idea that huC-activation by traditional allergenic extracts is mainly due to by-stander degradation products of the melanoidin (Maillard) or tannin type, which may or may not occur in physical association with the IgE-binding protein allergens.