Trichinella spiralis: synthesis of type IV and type VI collagen during nurse cell formation.

The portion of skeletal muscle fiber (Nurse cell) harboring Trichinella spiralis is surrounded by an acellular capsule susceptible to digestion with collagenase. Antibodies recognized type IV and type VI collagen in the capsule, while the periodic acid Schiff reagent stained the capsule differentially, revealing at least two distinct layers. RNA analysis showed that mRNA specific for type IV and type VI collagen was present in muscle tissue on Days 9 and 15, but not on Day 3, following intracellular infection. In situ hybridization showed that most of the mRNA for both types was within the Nurse cell, and all enlarged Nurse cell nuclei were transcriptionally active for those messages. Synthesis of type IV collagen mRNA was absent by Day 24. In contrast, type VI collagen mRNA was still present at 24 days and 8 months. These results support the hypothesis that T. spiralis, either directly or indirectly, influences the synthesis of these two collagen types throughout its own developmental cycle in the Nurse cell.