BIOMEDICAL APPLICATIONS III: DELIVERY OF IMMUNOSTIMULANTS AND VACCINES - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 95

and thoroughly analyse the effect of these structures on the activation of the
complement system. As regards this last aspect, the complement system is a
group of about 35 soluble and cell-surface proteins in blood which recognise,
opsonise and remove invading micro-organisms, altered host cells (such as
apoptotic or necrotic cells) and other foreign materials. 25
Complement activation may occur by any of three mechanisms, which
have been classiied into “classical”, “lectin” and “alternative” pathways. In
the classical mechanism, the protein C1q, the recognition subunit of C1,
recognises activators essentially on the basis of charge and hydrophobic
interactions. In the lectin pathway, the mannan-binding lectin (MBL) binds
to targets via neutral sugar residues (e.g., mannose). The alternative pathway
starts by the binding of the protein C3b to the pathogen surface, and the
subsequent events are analogous to those of the classical pathway (Fig. 4.7).
Figure 4.7 Complement activation via classical (up) and alternative (down) pathways.
Reproduced from Wikimedia Commons ( http://en.wikipedia.org/wiki/Alternativ e_
complement_pathway ). See also Colour Insert.
A major premise in the biomedical application of CNTs relies on the
possibility that the body's immune system can recognise CNT materials 26 and
initiate an immune response. So far, the absence of intrinsic immunogenicity
of CNTs as carriers of bioactive meolecules, 23 the translocation of CNTs across
the cell membrane and their deposition inside the cytoplasm without being