Internalization of macromolecules into filarial parasites – Possible operation of host's anti-fecundity immunity inside adult filarial nematodes

Objectives: Immune effector mechanisms operating against large extracellular systemic pathogens, such as adult stages of filarial nematodes, are not clearly understood. The only immune effect on the adult worms appears to be directed towards embryos in adult worms. The role of IL-4 or TLR-4 in immune responses that inhibit embryogenesis in adult filarial worms has been well-documented. This host's immune responses that control embryogenesis (anti-fecundity immunity) are considered critical and were addressed in the current study. The current investigation demonstrated the possible operation of anti-adult immunity that could be functional against large stage adults. Methods: Adult filaria worms were pulsed with macromolecules such as Concanavalin A, Human immunoglobulins, and Rabbit immunoglobulins for 6 hrs, and entry of these molecules was demonstrated using flow cytometry. Filaria worms were also preincubated with Latrunculin A, an endocytic inhibitor, to explain if macromolecules enter by endocytosis. Results: Using the flow cytometry approach, we could show the entry of immunoglobulins into the uterine cavity of female Setaria digitata, a cattle-dwelling filarial parasite. Immunoglobulins were observed to bind to the surface of intrauterine stages of female worms. We also demonstrated the presence of bovine immunoglobulins in different embryonic stages in situ. Conclusions: Overall, experimental evidence demonstrates the existence of the host's immune molecules inside large-stage adult parasites. However, future studies are directed to understand the functional aspect of the presence of these effector molecules inside the adults.