Histochemical response of mice to mistletoe lectin I (ML I)

Mucosal immunogenicity of plant lectins in mice

The mucosal immunogenicity of a number of plant lectins with different sugar specificities was investigated in mice. Following intranasal (i.n.) or oral administration, the systemic and mucosal antibody responses elicited were compared with those induced by a potent mucosal immunogen (cholera toxin; CT) and a poorly immunogenic protein (ovalbumin; OVA). After three oral or i.n. doses of CT, high levels of specific serum antibodies were measured and specific IgA was detected in the serum, saliva, vaginal wash, nasal wash and gut wash of mice. Immunization with OVA elicited low titres of serum IgG but specific IgA was not detected in mucosal secretions. Both oral and i.n. delivery of all five plant lectins investigated ¿Viscum album (mistletoe lectin 1; ML-1), Lycospersicum esculentum (tomato lectin; LEA), Phaseolus vulgaris (PHA), Triticum vulgaris (wheat germ agglutinin (WGA), Ulex europaeus I (UEA-1) stimulated the production of specific serum IgG and IgA antibody after three i. n. or oral doses. Immunization with ML-1 induced high titres of serum IgG and IgA in addition to specific IgA in mucosal secretions. The response to orally delivered ML-1 was comparable to that induced by CT, although a 10-fold higher dose was administered. Immunization with LEA also induced high titres of serum IgG, particularly after i. n. delivery. Low specific IgA titres were also detected to LEA in mucosal secretions. Responses to PHA, WGA and UEA-1 were measured at a relatively low level in the serum, and little or no specific mucosal IgA was detected.

Induction of tumor necrosis factor expression by a lectin from Viscum album

A purified lectin (MLI) from Viscum album was used to test whether peripheral monocytes from human blood can be activated for the production of tumour necrosis factor (TNF). Cytotoxic activity was detected in the supernatant of MLI-stimulated monocyte cultures. This cytotoxic activity was completely inhibited by monoclonal antibodies to TNF alpha. Small amounts of soluble TNF protein were measured in a TNF alpha-specific enzyme-linked immunospecific assay system. Strong expression of TNF alpha mRNA was induced in human monocytes as well as in macrophage cultures from C3H/HeJ mice having a low response to endotoxin after 2 h of stimulation. Both chains of the MLI were found to induce TNF mRNA equally well in human monocytes. In macrophages of endotoxin-low-responder mice the toxic A chain was a better inducer of TNF mRNA than the galactose-specific lectin B chain. Thus, MLI has immunomodulating effects in activating monocytes/macrophages for inflammatory responses.