STAT1 deficiency in U3A cells is associated with high susceptibility to <i>T. cruzi</i> infection and impaired cellular responses to IFNγ.

<p>(A) Stimulation of HFF cells with IFNγ (5 ng/ml for 6 h) resulted in reduced numbers of intracellular <i>T. cruzi</i> amastigotes as determined by conventional crystal violet and May-Grünwald staining. As indicated, cells were either left untreated (w/o IFNγ) or treated with IFNγ (+IFNγ) before being infected with trypomastigotes of the Brazilian Y strain of <i>T. cruzi</i> at MOIs of 0, 2 and 10, respectively (n = 2 in duplicate). (B-E) The histograms depict the average number of infected cells per microscopic field (B,D) and the average number of intracellular amastigotes per cell (C,E) in untreated HFF cells (black columns) and cells pre-treated with IFNγ (grey columns) for 6 h (B,C) and 24 h (D,E), respectively. Fibroblasts were infected with parasites at 2 or 10 MOI before parasite burden was quantified microscopically. (F,G) No inhibitory effects of IFNγ pre-treatment on <i>T. cruzi</i>-infected U3A cells lacking STAT1 expression. Similar experiment with respect to stimulation of cells with IFNγ, incubation with parasites and measurement of parasite invasion as described in (D,E), except that U3A cells were used.