Neutrophil depletion during Toxoplasma gondii infection leads to impaired immunity and lethal systemic pathology

The immunomodulatory role of neutrophils during infection with Toxoplasma g ondii was investigated. Monoclonal antibody-mediated depletion revealed tha t neutrophils are essential for survival during the first few days of infec tion. Moreover, neutrophil depletion was associated with a weaker type 1 im mune response as measured by decreased levels of gamma interferon, interleu kin-12 (IL-12) and tumor necrosis factor alpha. IL-10 was also decreased in depleted animals. Additionally, splenic populations of CD4(+) T cells, CD8 (+) T cells, and NK1.1(+) cells were decreased in depleted mice. Neutrophil -depleted mice exhibited lesions of greater severity in tissues examined an d a greater parasite burden as determined by histopathology and reverse tra nscription-PCR. We conclude that neutrophils are critical near the time of infection because they influence the character of the immune response and c ontrol tachyzoite replication.