Critical Role for Interleukin-25 in Host Protective Th2 Memory Response against Heligmosomoides polygyrus bakeri

Abstract

Infection with parasitic nematodes, especially gastrointestinal geohelminths, affects hundreds of millions of people worldwide and thus poses a major risk to global health. The host mechanism of defense against enteric nematode infection remains to be fully understood, but it involves a polarized type 2 immunity leading to alterations in intestinal function that facilitate worm expulsion. We investigated the role of interleukin-25 (IL-25) in host protection against Heligmosomoides polygyrus bakeri infection in mice. Our results showed that Il25 and its receptor subunit, Il17rb, were upregulated during a primary infection and a secondary challenge infection with H. polygyrus bakeri Genetic deletion of IL-25 (IL-25^-/-) led to an attenuated type 2 cytokine response and increased worm fecundity in mice with a primary H. polygyrus bakeri infection. In addition, the full spectrum of the host memory response against a secondary infection with H. polygyrus bakeri was severely impaired in IL-25^-/- mice, including delayed type 2 cytokine responses, an attenuated functional response of the intestinal smooth muscle and epithelium, diminished intestinal smooth muscle hypertrophy/hyperplasia, and impaired worm expulsion. Furthermore, exogenous administration of IL-25 restored the host protective memory response against H. polygyrus bakeri infection in IL-25^-/- mice. These data demonstrate that IL-25 is critical for host protective immunity against H. polygyrus bakeri infection, highlighting its potential application as a therapeutic agent against parasitic nematode infection worldwide.

FIG 1

Upregulation of Il25 and its receptor in the intestines of mice infected with H. polygyrus bakeri. Mice received a primary infection or a secondary challenge infection with H. polygyrus bakeri and were studied at day 14 postinfection. qPCR was performed to measure the levels of mRNA expression in the small intestine. The fold changes were relative to the level of expression for the individual vehicle groups after normalization to the level of 18S rRNA expression. *, P < 0.05 versus the respective vehicle group; ϕ, P < 0.05 versus the respective primary infection group (n ≥ 5 for each group).

FIG 2

Impaired type 2 cytokine response to primary infection with H. polygyrus bakeri in mice deficient in IL-25. Mice received a primary infection with H. polygyrus bakeri. Segments of jejunum were collected at day 14 postinfection and analyzed by qPCR for the levels of expression of mRNA for type 2 cytokines (A), molecular markers for alternatively activated macrophages (B), and host defense effector molecules (C). The fold changes in levels of expression were relative to the levels of expression for the respective WT-vehicle groups after normalization to the level of 18S rRNA expression. *, P < 0.05 versus the respective vehicle group; ϕ, P < 0.05 versus the respective WT group. (D) The numbers of worm eggs were determined at 14 and 18 days postinfection (Dpi). *, P < 0.05 versus WT mice infected with H. polygyrus bakeri (WT-H. bakeri) (n ≥ 5 for each group).

FIG 3

Impaired host defense against a secondary challenge infection with H. polygyrus bakeri in mice deficient in IL-25. Mice were infected with H. polygyrus bakeri, cured with an anthelmintic drug, and reinfected with H. polygyrus bakeri infective larvae. (A) Numbers of adult worms in the intestines of mice euthanized at 10, 14, and 20 days postinfection (Dpi). *, P < 0.05 versus the WT group. N.D., not detected. (B to I) Segments of jejunum were collected at 10 and 14 days postinfection and analyzed by qPCR for the levels of expression of mRNA for the type 2 cytokines Il4 (B), Il5 (C), Il13 (D), alternatively activated macrophage markers Arg1 (E) and Chil3 (F), the general macrophage marker Adgre1 (G), and host defense effector molecules Retnlb (H) and Muc5ac (I). The fold changes in levels of expression were relative to the levels of expression for the respective WT-vehicle groups after normalization to the level of 18S rRNA expression. *, P < 0.05 versus the respective vehicle group; ϕ, P < 0.05 versus the respective WT group (n ≥ 5 for each group).

FIG 4

Attenuated intestinal smooth muscle hypercontractile responses to H. polygyrus bakeri infection in mice deficient in IL-25. Mice were infected with H. polygyrus bakeri, cured with an anthelmintic drug, and reinfected with H. polygyrus bakeri infective larvae. Mice were euthanized at day 14 postinfection, and the intestinal strips were suspended longitudinally in organ baths for in vitro contractility studies in response to acetylcholine (10 nM to 0.1 mM) (A) and EFS (1 to 20 Hz, 100 V) (B). VEH, vehicle. (C) Representative H&E-stained intestinal sections from mice euthanized at 10 or 14 days postinfection (Dpi). Magnification, ×100. (D) The thickness of the smooth muscle layer was measured by microscopic examination of the H&E-stained intestinal sections. *, P < 0.05 versus the respective vehicle group; ϕ, P < 0.05 versus the respective WT group (n ≥ 5 for each group).

FIG 5

Attenuated intestinal epithelial hyposecretion and delayed mucosal permeability increase in mice deficient in IL-25 in response to infection with H. polygyrus bakeri. Mice were infected with H. polygyrus bakeri, cured with an anthelmintic drug, reinfected with H. polygyrus bakeri infective larvae, and euthanized at day 10 or 14 postinfection (Dpi). Muscle-free mucosa was mounted in Ussing chambers for the epithelial secretory response to acetylcholine (A) or in a microsnap well system for the measurement of TEER (B). *, P < 0.05 versus the respective vehicle group; ϕ, P < 0.05 versus the respective WT group (n ≥ 5 for each group).

FIG 6

Exogenous IL-25 restores the protective memory response against H. polygyrus bakeri infection in mice deficient in IL-25. WT or IL-25^−/− mice were infected with H. polygyrus bakeri, cured with an anthelmintic drug, and reinfected with H. polygyrus bakeri infective larvae. IL-25 or BSA, as a control, was injected into mice every other day starting at 5 days post-secondary infection, and the mice were euthanized at 10 days post-secondary infection (10 Dpi) (C) or 14 days post-secondary infection (A, B). (A) Numbers of adult worms in the intestines of mice at 14 days postinfection. Segments of jejunum collected at 10 days postinfection (C) and 14 days postinfection (B) were analyzed by qPCR for expression of mRNA for Il13, Arg1, and Retnlb. The fold changes in the levels of expression were relative to the levels of expression for the respective WT-vehicle groups after normalization to the levels of 18S rRNA expression. *, P < 0.05 versus the respective vehicle group (B) or WT mice infected with H. polygyrus bakeri and treated with BSA (WT-H. bakeri-BSA) at 10 days postinfection (C); ϕ, P < 0.05 versus the respective BSA group (n ≥ 5 for each group).