Proceedings of The Physiological Society

Puerto de la Cruz, Tenerife (2003) J Physiol 548P, P169

Poster Communications

Role of macrophage inflammatory protein-2 in a rat model of febrile neutropaenia

R. Maldonado, M.L. Ojeda, E. Tavares, D. Chbihi, A. Fernández-Alonso and F.J. Miñano

Unidad de Investigación, División de Farmacología Experimental y Clínica, Hospital de Valme, Facultad de Medicina, Universidad de sevilla, Ctra de Cádiz s/n, Sevilla, 41014, Spain

Gram-negative bacteriaemia is one of the most important causes of persistent fever and dose-limiting in the management of neutropaenic patients. The purpose of this study was to investigate and compare the role of macrophage inflammatory protein-2 (MIP-2), a powerful murine chemotactic factor for neutrophils, in the development of fever induced by bacterial endotoxin in both normal and neutropaenic animals. We show in a rat model of chemotherapy-induced neutropaenia that intraperitoneal injection of bacterial endotoxin (lipopolysaccharide, LPS) produced a fever whose magnitude was equal to or greater than that observed in normal animals.

Neutropaenia was induced in male Wistar rats (250-275 g, CRIFFA, Barcelona) by two intraperitoneal injections of cyclophosphamide (CP) of 150 mg kg-1 on day -4 and 50 mg kg-1 on day -1 (before LPS treatment). In this model of neutropaenia, the absolute neutrophil counts are very low (< 50 mm3) for 5-7 days. Also, the number of lymphocytes and monocytes are reduced, but not as strongly as the neutrophils (Bhattacharjee et al. 1994). In all experiments, the control groups received sterile saline as a placebo by the same route. Core body temperature (Tb) (± 0.1 °C) of each rat was measured by biotelemetry using precalibrated transmitters implanted intraperitoneally (Mini Mitter, Sunriver, OR), under aseptic conditions, at least 7 days before the onset of experimentation; the rats were anaesthetized with a mixture of ketamine and xylazine (Miñano et al. 1996). The kinetics of MIP-2 production were measured by specific ELISA (BioSource International, Camarillo, CA) in normal and CP-treated rats challenged with LPS.

For in vivo blocking experiments, a dose of 350 µg kg-1 neutralizing anti-MIP-2 (goat plyclonal antibody raised against rat MIP-2; Santa Cruz Biotechnology), was administered intraperitoneally, 15 min before LPS. Positive reference control animals received the same dose of an affinity-purified normal goat IgG (Santa Cruz Biotechnology). The present data show an increased MIP-2 production upon LPS challenge in normal and neutropenic rats. Although this enhanced production of MIP-2 is accompanied by an increased susceptibility of neutropenic rats to a febrile response with LPS, MIP-2 increase is responsible for the late phase of the febrile response induced by LPS in normal, but not in neutropenic, animals. By contrast, the specific neutralization of MIP-2 results in a partial reduction of the initial phase of LPS-induced fever in neutropenic rats but not in immunocompetent animals. Thus the present study indicates that blocking of MIP-2 bioactivity in vivo results in decreased endotoxin fever in normal but not neutropenic animals. These results are also the first demonstration that the chemokine MIP-2 is involved in the pathogenesis of a fever triggered by a gram-negative bacterial infection.

Where applicable, experiments conform with Society ethical requirements