Eosinophils, but Not Eosinophil Peroxidase or Major Basic Protein, Are Important for Host Protection in ExperimentalBrugia pahangiInfection

Abstract

The attenuation of eosinophilia by the administration of monoclonal antibodies to CCR3 consistently correlates with impairment in worm elimination following primary intraperitoneal Brugia pahangi infections in mice. Host protection was unimpaired in mice deficient in eosinophil peroxidase (EPO) or major basic protein 1 (MBP-1), suggesting that eosinophils are essential in host protection but that neither EPO nor MBP-1 alone is.Despite the consistent association of eosinophilia with parasitic infections, evidence supporting a host-protective role in vivo remains elusive (1-4, 16, 22). The function of eosinophils has been studied by modulating their numbers by manipulating interleukin-5 levels (5) (13) or depleting them selectively with a monoclonal antibody against the eotaxin receptor CCR3 (8). Eosinophilia correlates with improved host protection in Angiostrongylus cantonensis (19), Strongyloides ratti (17), Strongyloides stercoralis (12), Onchocerca volvulus (14), and Litomosoides sigmodontis (15) infections. In contrast, the depletion of eosinophils did not alter the course of Schistosoma mansoni (20), Mesocestoides corti (13), and Trichuris muris (3) infections. In the case of filarial parasites, eotaxin and eosinophils have been shown to play a role in host protection (21).The role of eosinophil granule constituents in host protection is also unclear. Purified eosinophil granule proteins have been shown to effectively kill Brugia microfilariae (11), schistosomulae (2), and Trichinella spiralis newborn larvae (10) in vitro. have shown that the death of onchocercal microfilariae following amocarzine treatment was associated with eosinophil degranulation. Electron microscopy analyses showed apposition of eosinophil granule material on the microfilarial surface. However, the requirement of eosinophil granule protein for in vivo host protection has not been studied extensively. In a recent study, EPO Ϫ/Ϫ and wild-type (WT) mice challenged with O. volvulus manifested similar parasite recoveries, suggesting that eosinophil peroxidase (EPO) is not required for host protection in this model (1). In order to investigate the role of the eosinophil granule proteins in host protection, we have now examined the course of Brugia pahangi infection in mice that have undergone targeted mutations in the genes encoding two of the major proteins in the eosinophil granules.C57BL/6 (hereafter WT) mice were obtained from the Jackson Laboratory (Bar Harbor, Maine). EPO Ϫ/Ϫ and MBP-1 Ϫ/Ϫ mice (6, 7) were transferred from the Mayo Clinic, Scottsdale, Arizona, where they were generated and backcrossed with C57BL/6 mice for six generations at the UCHC AAALACaccredited facility. Brugia pahangi third-stage larvae (L3) were provided by one of the following sources: TRS Inc. Monoclonal antibodies against rat RT 6.1 (DS4.23) and 6.2 (6A5) were obtained from Dale Greiner, UMass Medical Center, Worcester, MA. Antibodies were enriched from hybridoma ascites fluid by 50% ammonium sulfate precipitation. The precipitate was dialyzed against phos...

Lack of Eosinophil Peroxidase or Major Basic Protein Impairs Defense against Murine Filarial Infection

“…This may explain why a recent study failed to show a role for EPO or MBP in C57BL/6 mice infected with Brugia pahangi (37). Whether the deficiency of either granule protein on a fully permissive background such as BALB/c would also lead to a higher worm load is also an interesting question that could help determine whether the protective role for IL-5 is mediated through eosinophils or a separate effector mechanism.…”

“…Studies with O. volvulus, a nonpermissive filarial parasite in mice, did not detect a difference between EPO Ϫ/Ϫ and wild-type mice in L3 to L4 molting capacity (1). In experimental Brugia pahangi infection, also nonpermissive in mice, neither deficiency of EPO nor MBP led to an alteration of parasite loads, whereas administration of an eosinophil-depleting anti-CCR3 antibody resulted in higher parasite numbers, suggesting that eosinophils, but not EPO or MBP, are important for parasite control in this model (37).…”

Major Basic Protein from Eosinophils and Myeloperoxidase from Neutrophils Are Required for Protective Immunity to Strongyloides stercoralis in Mice

“…Protective immunity in immunized mice to the larvae of O. volvulus is dependent on eosinophils but was unaffected in EPO Ϫ/Ϫ mice (1). Studies performed on B. pahangi in mice deficient in MBP or EPO also concluded that eosinophils were essential for protective immunity, yet neither MBP nor EPO was required (54). In contrast, both MBP and EPO are required for protective immunity to Litomosoides sigmodontis in mice (61).…”

“…Specific ablation of eosinophils with a monoclonal antibody (MAb) to chemokine receptor type 3 (CCR3) (24) in mice immunized against the nematode O. volvulus not only eliminated protective immunity but also significantly increased the survival of the parasites in immunized mice to levels exceeding those seen in the controls (1). Elimination of eosinophils with the anti-CCR3 MAb also blocked resistance to primary infections with Brugia pahangi (54). Similar observations were made studying resistance to T. spiralis using CCR3-knockout mice, where there was an absence of eosinophil recruitment with a concomitant elevation in larval parasite survival (25).…”

Role of Eosinophils and Neutrophils in Innate and Adaptive Protective Immunity to LarvalStrongyloides stercoralisin Mice

“…An anti-CCR3 MAb (6S2-19-4) has been shown to specifically reduce the number of eosinophils in the peripheral blood of mice infected with Nippostrongylus brasiliensis to levels below those in naïve mice, without affecting other cell populations (24). Furthermore, treatment of mice with the anti-CCR3 MAb significantly reduced protective immunity to the filarial worms Onchocerca volvulus (1) and Brugia pahangi (49). A similar observation was made in a study of resistance to Trichinella spiralis using CCR3 Ϫ/Ϫ mice, where there was an absence of eosinophil recruitment along with a concomitant increase in larval parasite survival (25).…”