Particle size of latex beads dictates IL-1β production mechanism

Our plain-English summary of Particle size of latex beads dictates IL-1β production mechanism, by T. Adachi, K. Takahara, J. Taneo, et al (PloS One, 2013).

The study

• Authors: T. Adachi, K. Takahara, J. Taneo, Y. Uchiyama, K. Inaba
• Journal: PloS One
• Published: 2013;8(7):e68499
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Macrophages (Mϕ) are well documented to produce IL-1β through various signaling pathways in response to small particles such as silica, asbestos and urea crystals, in the presence of lipopolysaccharide (LPS). However, it has not been clear to what extent particle size affects the response. To investigate this point, we stimulated bone marrow-derived macrophages (BMDM) with size-defined latex beads (LxB). Although both nano-sized (20 nm) and micro-sized (1,000 nm) LxB induced IL-1β production, only the nano-sized particles formed large intracellular vacuoles. In contrast, 100 nm LxB did not induce either of the responses. The same cellular responses were also observed in primary microglia cells. Although K(+) efflux and NLRP3 activation in BMDM were crucial in response to both 20 and 1,000 nm LxB, only IL-1β production by 20 nm LxB was sensitive to cathepsin B and P2X7, a receptor for ATP. The response by 1,000 nm LxB relied on a robust production of reactive oxygen species (ROS), since IL-1β production was remarkably reduced by ROS inhibitors such as diphenylene iodonium (DPI) and N-acetylcysteine (NAC). In contrast, IL-1β production by 20 nm LxB was augmented by NAC and in BMDM deficient in thioredoxin-binding protein-2 (TBP-2), a negative regulator of the ROS scavenger thioredoxin. These results suggest that the cells responded differently in their secretion of IL-1β depending on particle size, and that there is a range within which neither pathway works.

In plain English

This laboratory study used mouse immune cells, not people. It did not test asbestos, which appears only in descriptions of other researchers' work. The authors grew macrophages, a type of immune cell, from mouse bone marrow. They exposed them to uniform latex beads 1,000, 100 or 20 nanometres across, plus LPS, a bacterial substance. They then measured IL-1β, an inflammatory signal. The 20 nm and 1,000 nm beads, but not the 100 nm beads, led to IL-1β production; LPS alone did not. Only the 20 nm beads produced vacuoles, large spaces inside the cells. Brain immune cells called microglia showed the same patterns. For both sizes, the response needed potassium to leave the cell and a protein called NLRP3. The 20 nm response depended on an enzyme called cathepsin B; cells lacking P2X7, a receptor for ATP, made less IL-1β with these beads. The 1,000 nm response depended on reactive oxygen species; the antioxidant NAC markedly reduced it. The authors concluded that the cells used different routes depending on particle size, with a size range where neither route worked.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment on mouse cells grown in culture (in vitro)
• Who was studied: Macrophages grown from the bone marrow of BALB/c and C57BL/6 mice, including mice lacking specific genes (NLRP3, P2X7, cathepsin B, cathepsin D, Parkin, TBP-2), plus primary microglia cells from postnatal mouse brains. Kyoto University, Japan. The number of animals is not stated.
• Exposure: Carboxyl latex beads of 1,000 nm, 100 nm or 20 nm diameter (also 30 and 300 nm, data not shown). Doses were 0.02% (v/v) in plate culture; in stirred culture, 0.06% for the 1,000 nm beads and 0.02% for the 100 and 20 nm beads. All with or without 10 ng/ml LPS, for 24 h in plates or 9 h in stirred culture. No asbestos or other mineral fibers were tested.
• Main results:
  • In mouse macrophages with LPS, the 1,000 nm and 20 nm beads, but not the 100 nm beads, induced IL-1β production. LPS alone did not.
  • Only the 20 nm beads caused vacuoles to form inside the macrophages.
  • Primary microglia cells showed the same changes in cell shape and the same IL-1β patterns.
  • Potassium leaving the cell (K+ efflux) and NLRP3 activation were needed for IL-1β, but not TNF-α, with both the 1,000 nm and 20 nm beads.
  • A cathepsin B inhibitor reduced IL-1β with the 20 nm beads but not with the 1,000 nm beads. The authors stated that cathepsin B is required for IL-1β production, but not vacuole formation, with the 20 nm beads.
  • Macrophages lacking the P2X7 receptor made less IL-1β only in response to the 20 nm beads; the authors described P2X7 as involved.
  • Strong production of reactive oxygen species inside the cells occurred only with the 1,000 nm beads. The response to the 20 nm beads was very weak.
  • The antioxidant NAC markedly reduced IL-1β with the 1,000 nm beads but increased it with the 20 nm beads.
  • In TBP-2-deficient macrophages, IL-1β was significantly increased compared with normal cells with the 20 nm beads, but not with the 1,000 nm beads.
• The authors' conclusion: The authors concluded that different-sized particles mainly used different signalling routes in mouse macrophages. Some key steps, NLRP3 activation and K+ efflux, were shared. Nano-size beads relied on cathepsin B and ATP-sensitive pathways, and micro-size beads relied on reactive oxygen species. They also concluded there is a size range within which neither pathway works.
• Limitations the authors state:
  • The authors stated that why the 100 nm beads did not induce IL-1β is unexplained and needs future experiments.
  • The authors stated that how the small amount of reactive oxygen species seen with the 20 nm beads inhibited IL-1β is not clear.
  • The authors noted that other researchers found the surface chemistry of particles affected responses. Results may therefore depend on the material and not only on size.
  • The authors stated that other pathways may be involved in the response to the 1,000 nm beads.

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Reactive Oxygen Species (ROS).

Related studies

• Size-dependent superparamagnetic iron oxide nanoparticles dictate interleukin-1β release from mouse bone marrow-derived macrophages — S. Chen, S. Chen, et al. (2018)
• Stimulation of oxidant production in alveolar macrophages by pollutant and latex particles — G.E. Hatch, D.E. Gardner, et al. (1980)
• Differential Regulation of IL-1β and IL-6 Release in Murine Macrophages — S. Hirano, Q. Zhou, et al. (2017)
• Gadolinium-based compounds induce NLRP3-dependent IL-1β production and peritoneal inflammation — C. Schmidt-Lauber, L. Bossaller, et al. (2015)
• Long, needle-like carbon nanotubes and asbestos activate the NLRP3 inflammasome through a similar mechanism — J. Palomäki, E. Välimäki, et al. (2011)
• Differences between particulate and peptide stimuli on activation of oxidant production in alveolar macrophages — G.E. Hatch, A. Spock, et al. (1980)

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