Changes in the structure of Nippostrongylus brasiliensis intestinal cells during development from the free-living to the parasitic stages.

The ultrastructure of Nippostrongylus brasiliensis intestinal cells was examined in free-living, feeding second-stage larvae, infective, nonfeeding third-stage larvae, and parasitic, feeding third-stage larvae. The intestinal cells of second-stage larvae were characterized by a well-developed microvillar border, large numbers of ribosomes, Golgi complexes, rough endoplasmic reticulum, and nuclei with prominent nucleoli. The intestinal cells of infective, third-stage larvae had very few microvilli and the cells were extremely narrow. Few ribosomes, Golgi complexes, and little rough endoplasmic reticulum were present. Nuclei did not contain nucleoli. When worms were introduced into an in vitro culture system, development of intestinal cells began. By 36 hr, microvilli were well differentiated and the cysoplasm contained numerous ribosomes and Golgi complexes, and rough endoplasmic reticulum, mitochondria, and nucleoli were prominent. These morphological changes were related to changes in the physiology of Nippostrongylus brasiliensis which occur during development from a free-living to parasitic form.

Initiation of development in vitro of third-stage Nippostrongylus brasiliensis.

Third-stage larvae of Nippostrongylus brasiliensis were maintained in vitro in 5 different culture systems at 25 C and 37 C, and initiation of development to the parasitic phase was evaluated at the morphological and biochemical levels. A few larvae grown in Krebs-Ringer-Tris solution at 25 C showed minimal development of the anterior region and intestinal cells. The amount of development was enhanced with an increase in medium complexity. At 25 C the greatest development was obtained in NCTC-135 : calf serum (8 : 2/v : v). Temperature elevation from 25 C to 37 C had a more significant effect on development than increasing the complexity of the culture medium. The number of L3 showing development in Krebs-Ringer-Tris at 37 C was significantly greater than the number maintained at 25 C in NCTC-135 : calf serum. Likewise, RNA biosynthesis was greatest in those larvae grown in NCTC-135 : calf serum at 37 C. These results support the idea that an elevation of temperature and certain nutritional components stimulate the transcription of that portion of the genome coding for development into the parasitic phase of the life-history.