Fibronectin- and laminin-mediated endocytic activity in the parasitic protozoa Trichomonas vaginalis and Tritrichomonas foetus.

The pathogenic protozoan Tritrichomonas foetus is able to ingest polystyrene particles with a diameter up to 1.0 micron. Trichomonas vaginalis, however, ingest particles as large as 4.4 microns in diameter. The particles are found within cytoplasmic membrane-bounded vacuoles. Morphometrical analysis showed that T. vaginalis presents a higher endocytic activity than T. foetus. Coating of the polystyrene particles with cationized ferritin increases their binding to the parasite surface but does not interfere with their ingestion. In contrast, coating with laminin significantly increased the uptake of the particles by both parasites while coating with fibronectin potentiates the ingestion of the particles only by T. foetus. These observations suggest the presence of laminin- and fibronectin-binding sites on the surface of trichomonads, an observation which is in agreement with the recent description of a receptor for laminin on the surface of trichomonads.