Role of Interferon-γ against Invasion byToxoplasma gondiiin a Human Monocytic Cell Line (THP1): Involvement of the Parasiteʹs Secretory Phospholipase A2

We examined the role of IFNγ in protection againstToxoplasma gondiiin the monocytoid cell line THP1. The addition of IFNγ to cultured infected THP1 cells reduced the number of parasited cells without altering intracellular multiplication during the first 24 hr. This reduction was potentiated by bacterial lipopolysaccharide (LPS). We also examined the role of an enzyme important forT. gondiicellular invasion, secretory phospholipase-A2 (sPLA2) and its relation with IFNγ-induced protection. Treatment of cells or parasites with a specific inhibitor of sPLA2 significantly reduced the number of infected cells at 6 hr. The addition of exogenous sPLA2 fromNaja najavenom did not interfere with the protective effect of IFNγ and confered protection when used alone. PLA2 activity was measured in supernatants of parasites maintained in the presence of IFNγ, and the results suggested that IFNγ opposes cell invasion byT. gondiiby suppressing parasite production of PLA2.