*Purpose: Previously our group assessed the spontaneous and lipopolysaccharide-induced NETosis with confocal microscopy in kidney transplant recipients (KTR). We found an enhanced spontaneous NETosis regardless of whether they had rejection compared to the donors. Therefore, we decided to extend the study focusing in patients with acute antibody-mediated rejection (AAMR).

*Methods: The purpose of this exploratory study was to evaluate the in vivo NETosis in plasma and tissue samples of adult KTR with AAMR (n=14) and compare them with KTR without any immunologic event (n=14). We used healthy donors (n=12) as the reference group. In vivo NETosis was evaluated by a sandwich ELISA to detect the plasmatic citrullinated histone 3-DNA complexes. The amount of NETS was quantified with the Optic Density Index (ODI). In renal biopsies, the expression of myeloperoxidase (MPO) and citrullinated histone 4 (cH4) was evaluated by confocal microscopy.

*Results: KTR with AAMR had the higher amount of NETs (figure1). Only in 2 AAMR biopsies we found netting neutrophils with decondensed chromatin co-localizing with cH4 in the glomeruli (figure 2). Also, in the peritubular capillaries we detected polymorphonuclear cells with cytoplasmic MPO (figure 3).

*Conclusions: KTR, particularly those with AAMR show enhanced in vivo NETosis. Although more studies are needed, the higher amount of plasmatic NETs and the detection netting neutrophils in tissue sample from AAMR suggest a role of NETosis in the pathogenesis of this type of kidney rejection and a state of permanent activation of neutrophils..

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