Interaction of mannan-binding lectin with Trichinella spiralis glycoproteins, a possible innate immune mechanism

Complex and variable glycoconjugates presented by parasitic nematodes during infection are very important in the host-parasite interplay. Predominantly carbohydrate-rich antigens are involved in the stimulation and modulation of the stage-specific immune response of the host. The non-specific innate immune system, however, acts as the first line of host defence against pathogens, before the appearance of antigen-specific responses. The functional entities of the innate system are lectins that recognize the surface ligands of pathogens: mannan-binding lectin (MBL) is a key recognition element involved in binding oligosaccharide structures exposed on microorganisms. In the present study we investigated whether MBL binds to the parasitic nematode Trichinella spiralis (T. spiralis). Since the parasite is coated with mannose-containing glycans, these structures could represent potential ligands for MBL and contribute to activation of the innate immune response of the host. Histochemical staining revealed MBL on the surface and internal organs of T. spiralis muscle larvae. MBL bound in a mannose-inhibitable manner to both crude extracts of T. spiralis muscle larvae and larvae excretory/secretory products. Western blot analyses showed that MBL recognized glycoproteins from all stages of T. spiralis. In vitro complement activation assays suggested that MBL is capable of fixing complement components on T. spiralis crude extract coated plates and activating the complement cascade through the 'lectin pathway'.