Alterations of the microcirculatory network during the clearance of epimastigote forms of Trypanosoma cruzi: An intravital microscopic study

The distribution of epimastigote forms of Trypanosoma cruzi in the microcir culatory network and thr vessel alterations were observed using an intravit al microscopy technique. Immediately after intravenous inoculation of 2 x 1 0(6) epimastigote suspension into normal mice, parasites were seen as circu lating clumps, and their retention at some sites of the endothelium of venu les and capillaries was observed. Injection of 2 x 10(7) and 2 x 10(8) para site suspensions induced, respectively, intermittent or total stasis of ven ules and capillaries, probably via obstruction by clumping. The mobility of epimastigotes in the clumps indicates that parasites were alive in the lum en of vessels. The retention of clumps in thr capillaries, although intense , could only be observed when labeled parasites were inoculated. These resu lts suggest that the rapid clearance of epimastigote forms of T. cruzi from the blood circulation of mice may be due to the retention of parasites to the endothelium of venules and capillaries that, in turn, may facilitate ph agocytosis. This may be a mechanism by which mice are able to eliminate epi mastigote forms from the circulation. These findings are consistent with ou r previous observation, showing that epimastigotes are not lysed by complem ent activation but are phagocytosed and destroyed by a distinct population of blood cells.