Identification of a phenotypically and functionally distinct population of long-lived neutrophils in a model of reverse endothelial migration

Abstract

Recent studies have demonstrated that neutrophils are not a homogenous population of cells. Here, we have identified a subset of human neutrophils with a distinct profile of cell-surface receptors [CD54(high), CXC chemokine receptor 1(low) (CXCR1(low))], which represent cells that have migrated through an endothelial monolayer and then re-emerged by reverse transmigration (RT). RT neutrophils, when in contact with endothelium, were rescued from apoptosis, demonstrate functional priming, and were rheologically distinct from neutrophils that had not undergone transendothelial migration. In vivo, 1-2% of peripheral blood neutrophils in patients with systemic inflammation exhibit a RT phenotype. A smaller population existed in healthy donors ( approximately 0.25%). RT neutrophils were distinct from naïve circulatory neutrophils (CD54(low), CXCR1(high)) and naïve cells after activation with formyl-Met-Leu-Phe (CD54(low), CXCR1(low)). It is important that the RT phenotype (CD54(high), CXCR1(low)) is also distinct from tissue-resident neutrophils (CD54(low), CXCR1(low)). Our results demonstrate that neutrophils can migrate in a retrograde direction across endothelial cells and suggest that a population of tissue-experienced neutrophils with a distinct phenotype and function are present in the peripheral circulation in humans in vivo.

Constitutive neutrophil apoptosis: Mechanisms and regulation

“…Lastly, current understanding is that upon recruitment into tissue, neutrophils fulfill their immune functions, die, and then are cleared by macrophages within the tissue stroma [141,142]. However, there have been suggestions that neutrophils might be able to emigrate out of inflamed tissue and return to circulation [143,144]. Schwab et al showed that nonapoptotic neutrophils carrying engulfed zymosan can exit exudates and recirculate back to lymph nodes, providing a new route for resolving inflammation [145].…”

Up-Regulation and Activation of Eosinophil Integrins in Blood and Airway after Segmental Lung Antigen Challenge

“…Remarkably, eosinophils in BAL had strong homogeneous labeling for ␤ 2 and ␣ M . One possibility is that higher reacting subpopulations of circulating leukocytes represent cells that have undergone "retrograde" migration back to the blood from tissues, as has been demonstrated for zebrafish neutrophils in vivo (79) and human neutrophils in vitro (80). Blood sampling at various time points after Ag challenge, including times beyond 48 h, may shed further light on circulating eosinophil subpopulations.…”

Neutrophil integrin affinity regulation in adhesion, migration, and bacterial clearance

“…However, in the last decade, it has been appreciated that neutrophils can also reverse migrate from the tissue back into the bloodstream. 33,34 In vitro reverse migrated neutrophils presented a unique phenotype with high ICAM-1 and low CXCR1, a subset of neutrophils that is increased in the peripheral blood Figure 2. Schematic representation of the role of selectins and integrins in neutrophil rolling, adhesion, and migration from the vasculature into the tissues and back.…”

“…34 Most of the observations on reverse migration have been obtained from in vitro experiments, or with in vivo zebrafish models. Since this process is not easily visualized in mammals, definitive proof of its importance is scarce.…”