R 1 aDMan p12aDMan p13 R aDMan p13

Figure 4 Carbohydrate side chains of ML I according to Debray et al. (1992). There is no indication what kind of glykan chains 1-3 are localised in the heavy or light A chains or in the B chain of ML I.

Sandwich ELISA test-systems allow to identify ML I, ML III, and, at favourable concentration ratios, of ML I and ML III to ML II, and also ML II at higher concentrations and relations to ML III>5:1 (Tonevitsky et al., 1995, 1999). Franz et al. (1983) did not observed cross reactivity of anti-ML (ML I toxoid) and antiviscotoxin (A3) antibodies with ML I and viscotoxin A3 antigens and vice versa. However, Stein et al. (1998) demonstrated by Western blotting techniques that human anti-ML antibodies can be cross reactive to viscotoxins. Therefore further studies are necessary including complete pattern of ML and viscotoxins.

Biological activities of RIP 2 Viscum album lectins

The cytotoxic and immunomodulatory properties of mistletoe preparations and ML have been studied intensively in past years (see Büssing, this book). The ML were

Figure 5 Quaternary structure of ML I as determined by X-ray cristallography demonstrates a dimeric composition. ([AL-S-S-B]2) of ML I with light A chain according to Sweeney et al. (1998). The B chains have two sugar combining sites C2, C1 and C2', C1', respectively. At the A chains, one enzymatic combining site N and N', respectively, is localised. Dimerisation of two ML I monomers is performed by contacts mainly via the B chains including water molecules.

Figure 5 Quaternary structure of ML I as determined by X-ray cristallography demonstrates a dimeric composition. ([AL-S-S-B]2) of ML I with light A chain according to Sweeney et al. (1998). The B chains have two sugar combining sites C2, C1 and C2', C1', respectively. At the A chains, one enzymatic combining site N and N', respectively, is localised. Dimerisation of two ML I monomers is performed by contacts mainly via the B chains including water molecules.

suggested by some groups to represent the biological activity of mistletoe extracts used to treat tumour patients. On the other hand, there is growing evidence that different components of mistletoe, such as lectin binders like glycoproteins and oligo/ polysaccharides, viscotoxins and small molecular weight molecules, exert important biological effects in a direct or even indirect manner via stabilisation of lectins.

As shown in Table 3, which summarises the main biological activities of ML and their separated A and B subunits, the biological effects related to the mistletoe isolectin pattern of mistletoe extracts are a complex phenomenon characterised by cytotoxic and immunomodulatory effects (see Büssing, this book). ML are useful tools for the selective staining of microglia cells (Artigas et al., 1992), lymph node compartments (Pfüller and Niedobitek, 1998) and Alzheimer's plaque glycoproteins (Schumacher et al., 1994) While ricin and abrin are highly toxic in animals and humans when applied orally, there are no reports on similar effects of mistletoe preparations and extracts following oral uptake (Pusztai et al., 1998a, 1998b; Lavelle et al., 1999; see Stein, this

Table 3 Biological activities of MLs and their subunits.

biological activity

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