On the origin of low-density neutrophils.

Here we elaborate on the origin of low(er)-density neutrophils (LDNs) to better understand the variation found in literature. Supplemented with original data, we test the hypothesis that buoyant density of neutrophils is characterized by a spectrum that as a whole shifts to a lower density after activation. Both the 20% highest density (HDNs) and 20% lowest density (LDNs) neutrophils from healthy donors were isolated by Percoll of different densities. Using this method we found that LDNs were significantly better in T-cell suppression and bacterial containment than their 20% highest density counterparts. We found no statistically relevant differences in neutrophil survival or bacterial phagocytosis. Stimulation of healthy donor neutrophils with N-formyl-methionyl-leucyl-phenylalanine induced LDNs co-segregating with peripheral blood mononuclear cells after Ficoll separation. These in vitro induced LDNs showed increased activation markers compared to HDNs and were comparable to the activation markers found on the LDN fraction seen in patients with chronic inflammatory conditions such as present in cancer patients. This all fits with the hypothesis that the density of neutrophils is distributed in a spectrum partially coupled to maturation. Additionally a shift in this spectrum can be induced by in vitro stimulation or by activation in disease.