Interactions between Leishmania mexicana mexicana promastigotes and amastigotes and murine peritoneal macrophages in vitro

Abstract

Unstimulated adherent mouse peritoneal cells were cultured in vitro and infected with equal numbers of a single strain of Leishmania m. mexicana amastigotes (AM), virulent promastigotes (VP), avirulent promastigotes (AVP) and fixed promastigotes (FP). Duplicate May-Grünwald-Giemsa stained coverslips were examined at time intervals up to 13 days. By 3 hr post infection, the number of macrophages containing parasites varied between 60.5% (VP) and 84% (AM) for macrophages exposed to living parasites, compared to 6.5% for macrophages exposed for FP. However, variable numbers of parasites showed degenerative changes by 3 hr, and the number of macrophages containing morphologically intact parasites varied significantly between cells infected with AM (84%) and those infected with VP (42%) or AVP(40%). The mean number on intacte parasites/macrophage also differed significantly between AM-infected cells and living or fixed promastigotes-infected cells. Quantitation of intact and degenerated parasites indicated parasite multiplication, as well as destruction, in VP-infected cells and parasite survival and multiplication in AM-infecte monolayers; in contrast no evidence of parasite multiplication was seen in AVP-infected cells. Changes in the mono layer itself (cell loss and macrophage vacuolization) were also evaluated. These results suggest that crucial events determining the outcome of infection occur in the host-parasite relationship during the fist 24 hours of infection. These events are apparently influenced not only by parasite or host strain but by environmentally induced variation within a given strain.<br>Células peritoneais de camundongos cultivadas in vitro foram infectadas com inóculos idênticos de amastigotas (AM) e de promastigotas, respectivamente, virulentas (VP), avirulentas (AVP) e fixadas (FP) de uma mesma cepa de Leishmania m. mexicana. As monocamadas coradas com May-Grunwald-Giemsa foram examinadas em diferentes intervalos de tempo. Ao nível de 3ª hora pós-infecção o número de macrófagos contendo parasitas variou entre 60,5% (VP) e 84% (AM) nas monocamadas expostas aos parasitas viáveis, comparados com 6,5% para aquelas expostas aos parasitas fixados. Entretanto, nesse tempo de interação, houve alterações degenerativas parasitárias e o número de macrófagos contendo parasitas intatos variou significantemente entre as células infectadas com AM (84%) e aquelas infectadas com VP (42%) ou AVP (40%). O número médio de parasitas intatos/macrófago também diferiu significantemente entre as células infectadas com AM e aquelas infectadas com promastigotas viáveis ou fixadas. A análise quantitativa de parasitas intatos e degenerados indicou uma multiplicação e destruição parasitaria nas monocamadas infectadas com VP e sobrevivência e multiplicação parasitarias naquelas infectadas com AM. Em contraste, nao houve evidencia de multiplicacao de parasitas nas células infectadas com AVP. Esses resultados sugerem que os eventos cruciais que determinam a evolução da infecção ocorrem durante as primeiras 24 horas da intera...