BIOMEDICAL APPLICATIONS III: DELIVERY OF IMMUNOSTIMULANTS AND VACCINES - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 96

toxic 27 and inally their ability to enhance an immune response when attached
to an antigen 7 have reinforced the possibility of using CNTs as therapeutic
and vaccine delivery tools.
At the same time, very limited information is available on the interaction
between this nanomaterial and the immune system. Green and his research
group 14 recently reported an interesting study concerning the ability of
different types of CNTs to activate the human serum complement system
via the classical pathway. In this investigation, two types of CNTs were used:
single-walled (SWCNTs) and double-walled (DWCNTs). The nanotubes
were produced through different procedures and reported as arc discharge
(arc-SWCNTs), chemical vapour deposition CNTs (CVD-SWCNTs and CVD-
DWCNTs) and high-pressure carbon monoxide SWCNTs (HIPco-SWCNTs).
The major difference among them consisted of the amount of metal element
impurities still present after the puriication process: plasma atomic
emission spectroscopy analysis revealed that arc-SWCNTs contained 1.4%
(w/w) Ni, HIPco-SWCNTs 1% (w/w) Fe, CVD-SWCNTs 0.2% (w/w) Co, and
CVD-DWCNTs 1.9% (w/w) Mo. It was observed that all the CNT samples
tested activated complement to an extent comparable with zymosan, a well-
known complement activator through the classical pathway (Fig. 4.8): more
precisely, the mechanism of such activation seemed to involve a direct and
selective binding of C1q to CNTs, since the alternative mechanisms (e.g.,
direct binding of C3b [alternative pathway] to the CNTs, binding of CNTs to
ibrinogen, or even binding of C1q or C3b to other plasma/serum proteins,

a

b

(B)

Figure 4.8 (a) Percentage consumption of human serum complement activity via
classical pathway due to the presence of different types of carbon nanotubes. (b)
Percentage consumption of human serum complement activity via alternative
pathway due to the presence of two types of carbon nanotubes. Zymosan samples
were used as the positive control. A sample of undiluted human serum incubated at
37°C served as the negative control. Reproduced from Carolina Salvador-Morales et
al. 14 with permission.