Modulation of NK cell activation by exogenous calcium from alginate dressings in vitro

Abstract

Natural Killer (NK) cells participate in the defense against infection by killing pathogens and infected cells and secreting immuno-modulatory cytokines. Defects in NK cell activity have been reported in obese, diabetic, and elderly patients that are at high risk of developing infected chronic wounds. Calcium alginate dressings are indicated for the debridement during the inflammatory phase of healing. Since calcium ions are major activators of NK cells, we hypothesized that these dressings could enhance NK functions, as investigated in vitro herein. Primary human blood NK cells were freshly-isolated from healthy volunteers and exposed to conditioned media (CM) from two alginate dressings, Algosteril® (ALG, pure Ca2+ alginate) and Biatain® Alginate (BIA, Ca2+ alginate with CMC), in comparison with an exogenous 3mM calcium solution. Our results demonstrated that exogenous calcium and ALG-CM, but not BIA-CM, induced NK cell activation and enhanced their capacity to kill their targets as a result of increased degranulation. NK cell stimulation by ALG depended on the influx of extracellular Ca2+via the SOCE Ca2+ permeable plasma membrane channels. ALG-CM also activated NK cell cytokine production of IFN-γ and TNF-α through a partly Ca2+-independent mechanism. This work highlights the non-equivalence between alginate dressings for NK cell stimulation and shows that the pure calcium alginate dressing Algosteril® enhances NK cell cytotoxic and immuno-modulatory activities. Altogether, these results underline a specific property of this medical device in innate defense that is key for the cutaneous wound healing process.

In vitro effects of wound‐dressings on key wound healing properties of dermal fibroblasts

“…The amount of Ca 2+ released by ALG has been shown to induce calcium signalling and stimulate endothelial cell activation (Duciel et al., in preparation). Thus, the difference in Ca 2+ released between ALG and BIA could explain the differences observed in a previous study on NK cell activation 24 and in this study on fibroblast activation. Moreover, some dressings containing CMC have been reported to reduce fibroblast viability and proliferation and CMC inhibited NK cell cytolytic activity 16,24 …”

“…Although ALG and BIA are both calcium alginate dressings, they induced distinct cellular effects as reported in this study on fibroblasts and in a previous study on NK cells. 24 These discrepancies could be explained by differences in their composition. ALG is composed of 100% Ca 2+ alginate fibres, BIA is composed of Ca 2+ alginate fibres combined with CMC.…”

“…[45][46][47][48][49] In a previous study, ALG-CM was shown to enhance NK cell activities, notably pro-inflammatory cytokine production, which suggested that Algosteril stimulated NK cell-mediated defence during the inflammatory phase. 24 However, an inflammatory environment affects fibroblast activities necessary for granulation tissue formation and must be resolved for healing to proceed. 3 In this study, the supernatant of activated NK cells in the presence of ALG-CM was able to restore fibroblast migration, which is inhibited by activated NK cell supernatants.…”

“…NK cells were purified from isolated human peripheral blood mononuclear cells (PBMCs) as previously described. 24 NK cells first incubated with IL-2/IL-15 in complete CT RPMI1640 during 24 h, were then stimulated by the presence of LPS (1 μg/mL) in either CT or ALG CM for a further 18 h period.…”

“…ALG-CM was previously shown to stimulate activated NK cells, 24 and these cells may inhibit fibroblast migration. 4,5,7 Therefore, the effect of the supernatant of NK cells incubated or not with ALG-CM was analysed on fibroblast migration.…”