Metal Nanoparticles in Infection and Immunity

Abstract

Background Enthusiasm for the use of metal nanoparticles in human and veterinary medicine is high. Many articles describe the effects of metal nanoparticles on microbes in vitro, and a smaller number of articles describe effects on the immune system, which is the focus of this review. Methods Articles were retrieved by performing literature searches in Medline, of the National Institute of Medicine, as well as via Google Scholar. Results In vitro studies show that metal nanoparticles have antimicrobial effects. Some metal nanoparticles augment innate host immune defenses, such as endogenous antimicrobial peptides, and nitric oxide. Metal nanoparticles may also function as vaccine adjuvants. Metal nanoparticles can migrate to locations distant from the site of administration, however, requiring careful monitoring for toxicity. Conclusions Metal nanoparticles show a great deal of potential as immunomodulators, as well as direct antimicrobial effects. Before metal particles can be adopted as therapies; however, more studies are needed to determine how nanoparticles migrate though the body and on possible adverse effects.

Keywords: Gold; nitric oxide; silver; vaccine adjuvants; zinc.

Fig. 1.

Panel A, Results from the Medline database of the National Library of Medicine (NLM) from a search for articles on “Metal Nanoparticles,” indexed yearly from 2005 to 2019. Panel B, Illustration showing the categories into which articles on metal nanoparticles effects in infection and immunity can be sorted. Articles on metal particles for in vitro diagnosis and on metal particles used as carriers for other, known antimicrobials are not discussed in this review.

Fig. 2.

Interaction of Zinc Nanoparticles with Innate Immune Host Responses. Panel A, synergy between zinc oxide nanoparticles and the nitric oxide donor S-nitroso-acetyl-penicillamine (SNAP). Zinc oxide nanopowder was from Inframat Advanced Materials, Manchester, CT, and SNAP was from Enzo. The combination of ZnO nanoparticles and SNAP inhibited growth of E. coli strain B171–8, resulting in a zone of inhibition around the disk (red arrow). Panel B, cecropia moth, from which the antimicrobial peptides called cecropins were first isolated. Panel C, synergy between zinc oxide nanoparticles and cecropin A. ZnO particles alone failed to produce any zone of inhibition with E. coli strain B171–8 (disk on top left). Cecropin A alone produced a very small, barely detectable zone of inhibition (black arrow), but the combination of ZnO particles and cecropin A formed a definite zone of inhibition of growth (white arrow).