Hookworms are intestinal parasites that infect approximately 700 million people worldwide, mostly in tropical areas in underdeveloped countries. High-intensity infections with Ancylostoma duodenale and Necator americanus, the most common hookworm parasites in humans, cause anemia and protein deficiency that can result in delayed growth and mental development1. N. americanus and the rodent parasite Nippostrongylus brasiliensis induce a prototypical type 2 immune response in their host and share similarities in their life cycle. Hence, the infection of mice with N. brasiliensis is the most commonly used model for human hookworm infections. Stage 3 (L3) N. brasiliensis infective larvae move from the skin to the lung in the first few hours post-infection. Once in the lung, they become L4 and migrate up the trachea to get swallowed, pass through the stomach, and reach the gut to become adults (L5) within 4-5 days. In the gut, L5 worms lay eggs that are excreted in the feces to restart the parasite life cycle2.
The immune response induced by N. brasiliensis is characterized by an increase in several type 2 cytokines, including IL-4, IL-5, IL-9, IL-10, and IL-13, along with eosinophilia, basophilia, goblet and mast cell hyperplasia, and heightened IgG1 and IgE production. Most of the studies trying to identify and define the immune responses elicited upon N. brasiliensis infection are centered on the role of IL-4 or IL-13 in this model3. However, the identification and characterization of IL-9-expressing cells and the function of this cytokine had been largely overlooked, until Licona-Limón et al. published the first study demonstrating a critical role for IL-9 in the immune response against N. brasiliensis. Using reporter mice, this study described T cells (mostly T helper 9) and type 2 innate lymphoid cells (ILC2s) as the main cellular subsets expressing IL-9 upon infection4.
Isolation and characterization of immune cells from helminth-infected lungs is feasible, and has been extensively reported3,4. However, because of the inherent tissue remodeling and mucus production, to do so in the infected gut proved to be a technical challenge, until the recent publication of Ferrer-Font et al.5. The group outlined a protocol to isolate and analyze single-cell suspensions of immune subsets from Heligmosomoides polygyrus-infected murine intestines. Based on it , we have now standardized a protocol for isolation and cytometric analysis of IL-9-expressing lymphoid cells from the N. brasiliensis infected gut. In addition, we have established IL-9 kinetics from different cellular sources and anatomical locations throughout the infection.
Characterizing the distinct cell populations involved in this infection is vital for a wider understanding of the immune response to the parasite and its interaction with the host. This comprehensive protocol provides a clear route to isolate and analyze IL-9-producing cells from desired organs at disease stages of interest, allowing for a sharp improvement of the knowledge about the role of these cells in N. brasiliensis infection and parasite infections in general.