Characterization of neutrophil extracellular traps in cats naturally infected with feline leukemia virus

Feline leukemia virus (FeLV), a common, naturally occurring gammaretrovirus in domestic cats, is associated with degenerative diseases of the haernatopoietic system, immunodeficiency and neoplasia. FeLV infection causes an important suppression of neutrophil function, leading to opportunistic infections. Recently, a new microbicidal mechanism named NETosis was described in human, bovine and fish neutrophils, as well as in chicken heterophils. The purpose of the present study was to characterize NETosis in feline neutrophils, as well as to evaluate neutrophil function in FeLV naturally infected symptomatic and asymptomatic cats through the phagocytosis process, release of neutrophil extracellular traps (NETs) and myeloperoxidase (MPO) activity. The results showed that feline neutrophils stimulated with protozoa parasites released structures comprising DNA and histones, which were characterized as NETs by immunofluorescence. Quantification of NETs after neutrophil stimulation showed a significant increase in NET release by neutrophils from FeLV- and FeLV+ asymptomatic cats compared with FeLV+ symptomatic cats. Moreover, the number of released NETs and MPO activity in unstimulated neutrophils of FeLV+ symptomatic cats were higher than those in unstimulated neutrophils from FeLV- and FeLV+ asymptomatic cats. This study reports, for the first time, NET release by feline neutrophils, along with the fact that NET induction may be modulated by a viral infection. The results indicate that the NET mechanism appears to be overactivated in FeLV+ cats and that this feature could be considered a marker of disease progression in FeLV infection.