Nippostrongylus-induced intestinal hypercontractility requires IL-4 receptor alpha-responsiveness by T cells in mice

Abstract

Gut-dwelling helminthes induce potent IL-4 and IL-13 dominated type 2 T helper cell (T(H)2) immune responses, with IL-13 production being essential for Nippostrongylus brasiliensis expulsion. This T(H)2 response results in intestinal inflammation associated with local infiltration by T cells and macrophages. The resulting increased IL-4/IL-13 intestinal milieu drives goblet cell hyperplasia, alternative macrophage activation and smooth muscle cell hypercontraction. In this study we investigated how IL-4-promoted T cells contributed to the parasite induced effects in the intestine. This was achieved using pan T cell-specific IL-4 receptor alpha-deficient mice (iLck(cre)IL-4Rα(-/lox)) and IL-4Rα-responsive control mice. Global IL-4Rα(-/-) mice showed, as expected, impaired type 2 immunity to N. brasiliensis. Infected T cell-specific IL-4Rα-deficient mice showed comparable worm expulsion, goblet cell hyperplasia and IgE responses to control mice. However, impaired IL-4-promoted T(H)2 cells in T cell-specific IL-4Rα deficient mice led to strikingly reduced IL-4 production by mesenteric lymph node CD4(+) T cells and reduced intestinal IL-4 and IL-13 levels, compared to control mice. This reduced IL-4/IL-13 response was associated with an impaired IL-4/IL-13-mediated smooth muscle cell hypercontractility, similar to that seen in global IL-4Rα(-/-) mice. These results demonstrate that IL-4-promoted T cell responses are not required for the resolution of a primary N. brasiliensis infection. However, they do contribute significantly to an important physiological manifestation of helminth infection; namely intestinal smooth muscle cell-driven hypercontractility.

Figure 1. IL-4 responsive T cells are not needed for expulsion of N. brasiliensis.

iLck^creIL-4Rα^−/lox and control mice were infected with 750 N. brasiliensis L3 larvae. Faeces were collected from day 6 to 14 post infection (PI) and egg production was calculated using the modified McMaster technique (A). At days 7 and 10 PI the worm burden in the small intestine was assessed (pooled from 3 experiments) (B). Intestinal goblet cell hyperplasia was assessed by determining the total number of PAS-positive goblet cells per 5 villi in histological sections of the small intestine at day 7 and 10 PI (C). Mucus and PAS staining at days 7 and 10 PI. Representative photomicrographs are shown from individual mice and N. brasiliensis is indicated with a black arrow (D). Total IgE production in the serum was measured by ELISA at day 7 and 10 PI (E). The graphs show mean values ± SEM and represent the results of three independent experiments, except B and E where 2–3 independent experiments were combined with n = 4 or 5 mice per group. ND, not detected. One-Way-ANOVA, *P<.05, **P<.01, ***P<.001 for all experiments.

Figure 2. N. brasiliensis induced smooth muscle cell hypertrophy/hyperplasia is unaffected in iLck^creIL-4Rα^−/lox mice.

Haematoxylin and eosin stained sections were used to determine the smooth muscle cell layer thickness from Day 3, 7 and 10 N. brasiliensis-infected iLck^creIL-4Rα^−/lox and control mice. Representative photomicrographs are shown from control mice at days 3, 7 and 10 at 40× magnification. Also shown is a photomicrograph at 200× showing the longitudinal and circular smooth muscle layers included in the measurement (A). Measurements are shown in a bar graph (B) with mean values+SEM and represent 2 independent experiments with n = 4 or 5 mice per group. Ns = not significant. One-Way-ANOVA, ***P<.001.

Figure 3. Reduced IL-4 response in N. brasiliensis-infected iLck^creIL-4Rα^−/lox and IL-4Rα^−/− mice.

Mice were infected with 750 N. brasiliensis L3 larvae and at days 7 and 10 PI CD4⁺ cells from pooled mesenteric lymph nodes were isolated by negative selection (purity>90%) then restimulated with anti-CD3 for 48 hours and IL-4, IL-13, INF-γ, IL-17 cytokine concentration of the supernatant determined by ELISA (A). Further, IL-4 and IL-13 concentrations were determined in homogenates of the jejunum (B). The graphs show mean values+SEM and are representative of the results of three independent experiments with IL-17 only determined in one experiment for CD4⁺ T cells and IL-13 in two independent experiments for homogenates, with n = 4 or 5 per group. One-Way-ANOVA, *P<.05, **P<.01, ***P<.001.

Figure 4. N. brasiliensis-induced and IL-4Rα-mediated intestinal hypercontractility is impaired in iLck^creIL-4Rα^−/lox mice.

Jejunum pieces (1 cm) of non-infected and N. brasiliensis infected (PI day 7 and 10) mice were stimulated with KCl and contractility was measured (A). Comparison of the different mouse strains in response to acetylcholine is also shown for naïve, day 7 or day 10 infected IL-4Rα^−/lox, IL-4Rα^−/− and iLck^creIL-4Rα^−/lox mice (B). Contractility is shown as a mean value ± SEM for individual dose points. Graphs show three independent experiments with n = 12 in total. One-Way-ANOVA, *,# P<.05; **,## P<.01; ***,### P<.001. *indicates statistical significant differences between IL-4Rα^−/lox and IL-4Rα^−/−, # shows differences between IL-4Rα^−/lox and iLck^creIL-4Rα^−/lox mice.