Neutrophil Myeloperoxidase Index in Dogs with Babesiosis

Abstract

Babesiosis caused by the more virulent tick-borne haemoprotozoan, Babesia rossi, results in a marked systemic inflammatory host response in dogs. Neutrophils are part of the innate immune system and myeloperoxidase is the predominant component of the neutrophil lysosomal protein in azurophilic granules. This enzyme plays a crucial role in the process of destruction of microbes by neutrophils. Neutrophil myeloperoxidase index (MPXI) is a reflection of the intracellular myeloperoxidase content in circulating neutrophils. The aims of this study were to: (a) compare MPXI in dogs with babesiosis with healthy control dogs, using the ADVIA 2120; (b) compare MPXI in dogs that died from babesiosis with dogs that survived and controls; and (c) correlate the MPXI results with (i) total band and segmented neutrophil count and (ii) various cytokine concentrations. Data for 140 dogs, naturally infected with B. rossi, and 20 healthy control dogs were retrospectively evaluated. Approval was obtained from the University of Pretoria’s Animal Ethics committee, as well as the Faculty Research Committee. Owner consent was obtained for enrolment of each case. MPXI was generated on an automated cell counter, ADVIA2120, and various cytokine concentrations, including interleukin-2 (IL-2), IL-6, IL-8, IL-10, IL-18, granulocyte-macrophage colony stimulating factor (GM-CSF) and monocyte chemoattractant protein-1 (MCP-1), were determined using a canine-specific multiplex immunoassay (MILLIPLEX MAP Canine Cytokine/Chemokine Magnetic Bead Panel CCYTO-90K-07, Millipore, Billerica, USA). The mortality rate of the Babesia-infected dogs was 11% (15/140). MPXI was significantly higher in the Babesia-infected dogs (P = 0.033), as well as the Babesia-infected nonsurvivors (P = 0.011), compared to the controls. For the Babesia-infected group a significant positive correlation was found between MPXI and IL-10 (r = 0.211, P = 0.039), and a significant negative correlation between MPXI and IL-8 (r = -0.350, P < 0.001). For the dogs that died, significant positive correlations were found between MPXI and IL-2 (r =0.616, P = 0.033), IL-6 (r = 0.615, P = 0033), IL-18 (r = 0.613, P = 0.034), GM-CSF (r =0.630, P = 0.028) and MCP-1 (r = 0.713, P = 0.009). In dogs that survived, a significant negative correlation was found between MPXI and IL-8 (r = -0.363, P = 0.001). The higher MPXI value in Babesia-infected dogs and especially Babesia-infected nonsurvivors, in conjunction with cytokines, could indicate an increased inflammatory response, as is expected in B. rossi-infections. The potential of MPXI as a novel marker of inflammation and prognosis in Babesia rossi-infected dogs, warrants further exploration.