Effect of the cell-growth rate on the invasion and infection efficacy of Trypanosoma cruzi trypomastigotes, and the potential cell-to-cell transfer of the parasite

Abstract: Recent studies proposed that mammalian cell lines with slower growth rates were infected more efficiently by Trypanosoma cruzi, and that cell-to-cell transmission could be occurring during infection. This open the question of whether host cell-growth rate is a cellular characteristic influencing Trypanosoma cruzi invasion and infection. To prove if this was the case, the cell growth-rate was inhibited by starvation, reducing the foetal bovine serum concentration in the medium, and using a cell-cycle arresting drug, Baicalein. Then the percentage of infected cells of the control and the growth-modified group was measured via epifluorescence microscopy. The results did not show a strong evidence of negative correlation between the cell-growth rate and infection efficacy. To assess if cell-to-cell infection was occurring, the percentage of infected cells in contact with other infected cells was measured. This value was compared to the stochastic probability of this event happening. The results showed that the random probability of an infected cell being next to another infected cell was much lower than the percentage obtained from the empirical data. This suggests that cell-clusters found in infections are not a random event and that the dominant mechanism of infection is a short-range one: either by cell-to-cell infection, or by the proliferation of already infected cells. To support cell-to-cell transmission, parasites potentially passing from one cell to another were inspected through confocal microscopy and actin-rich regions were found at the parasite location. To determine whether actin played a role in this event, cells with a mutation in the actin gene were infected and compared to the mock group. The results showed that the percentage of infected cells in contact with other infected cells was lower for the mutant cells, suggesting that actin could play a key role in this event.