Human neutrophil heterogeneity: subsets, markers and autoantibodies

Abstract

ABSTRACT Neutrophils are phagocytic white blood cells that play essential roles in innate im-munity and inflammation. Neutrophils have traditionally been viewed as a homog-enous cell population, where all cells carry the same molecular cargo and have iden-tical functions. Lately, this view is changing and distinct subsets of neutrophils are being recognized. The aim of this thesis was to characterize neutrophil subsets and investigate the role of their markers as anti-neutrophil cytoplasmic (ANCA) anti-gens. The first paper investigated the recently discovered neutrophil subsets defined by the presence or absence of Olfactomedin-4 (OLFM4). We found that OLFM4 is indeed expressed by only a portion of the neutrophils from a given individual and that OLFM4 is a specific granule protein that can be exposed on neutrophil extracel-lular traps (NETs). We did not find any functional differences between the subsets in vitro, and the subsets migrated equally well into tissue in vivo, both to synovial fluid of arthritis patients and to aseptic experimental skin chamber on healthy skin. During routine testing for the presence of ANCA in the circulation of patients with suspected autoimmune disorders, we found sera from two patients with diffuse in-flammatory symptoms that displayed unusual staining patterns, reacting with only a subset of neutrophils. In the second paper, we identified the target antigen as OLFM4, and this was the first report of autoantibodies towards this subset marker. The third study began with two additional patient sera that gave rise to subset-restricted ANCA staining patterns. This time, we identified the target antigen as CD177, which is a known neutrophil subset marker and a known target of alloanti-bodies. CD177 has previously been shown to be of importance for trans-migration of neutrophils in vitro. However, using synovial fluid from arthritis patients and the experimental skin blister model, we found no evidence for a major general role of CD177 in in vivo neutrophil transmigration. In summary, we have characterized two bona fide neutrophil subsets and identified OLFM4 and CD177 as ANCA anti-gens.