Imiquimod Treatment Causes Systemic Disease in Mice Resembling Generalized Pustular Psoriasis in an IL-1 and IL-36 Dependent Manner

Abstract

Generalized pustular psoriasis (GPP) is a severe form of psoriasis that can be caused by missense mutations in the interleukin-36 (IL-36) receptor antagonist. In addition to neutrophil rich skin inflammation, GPP patients typically also experience anorexia, fever, malaise, and pain. The imiquimod-induced skin inflammation mouse model has rapidly become a popular way to study plaque psoriasis, which typically does not involve symptoms of systemic disease. In this model, neutrophil recruitment to the skin is dependent upon the inflammatory mediators IL-1, via its receptor IL-1R1, and IL-36α. Unexpectedly, we observed that mice also exhibited signs of anorexia (weight loss and decreased food intake), general malaise (decreased activity and loss of interest in building nests), and pain (nose bulging and hunched posture). A scoring system allowing quantitative comparisons of test groups was developed. Female mice were found to develop more severe disease than male mice. Furthermore, mice deficient in both IL-1R1 and IL-36α are nearly disease-free, while mice lacking only one of these inflammatory mediators have less severe disease than wild type mice. Hence, the imiquimod-induced skin inflammation mouse model recapitulates not only plaque psoriasis, but also the more severe symptoms, that is, anorexia, malaise, and pain, seen in GPP.

Figure 1

Generic imiquimod cream causes more severe disease than Aldara®. Male C57BL/6J mice (n = 4 per group) received daily treatments (a) with Aldara (black symbols) or generic (Perrigo®, open symbols) 5% imiquimod cream (62.5 mg). Weight ((b), expressed as percentage of values at day 0), survival (c), and skin inflammation (d) were monitored. Data from one representative experiment of at least 3 independent experiments is shown as means ± SD. ^∗ p < 0.05; ^∗∗ p < 0.01 (comparing Generic to Aldara at individual timepoints).

Figure 2

Topical imiquimod cream application causes systemic disease in mice resembling that observed in GPP patients. Male C57BL/6J mice (n = 4 per group) were treated daily with 62.5 mg 5% imiquimod cream (Perrigo, open bars and symbols) or were sham-treated (black bars and symbols). Behavioral changes (physical activity (a and b) and nest building (c and d)), pain (posture (e and f), nose bulging (g and h), and orbital tightening (i and j)), and anorexia (food intake (k and l) and mouse body weight (m)) were evaluated and scored as described in Table 1. Total disease scores (n) were calculated as the sum of individual scores for each mouse and group means (±SD) shown. ND: no disease detected, score = 0. Graphed data from one representative experiment of more than 3 independent experiments is shown as means ± SD. ^∗ p < 0.05; ^∗∗ p < 0.01; ^∗∗∗ p < 0.001 (comparing imiquimod to control at individual timepoints). Pictures from independent experiments were taken at day 4.

Figure 3

Female mice develop more severe disease than male mice in response to generic imiquimod cream. Wild type male (black bars and symbols) and female (open bars and symbols) mice (n = 4 per group) were treated with 31.25 mg imiquimod cream (Perrigo) once daily for a total of 4 applications. Activity (a), nest building (b), posture (c), nose bulging (d), weight (e), and food intake (f) were evaluated as described in Figure 2 and Table 1. ND: no disease detected, score = 0. Data shown (means ± SD) is from one representative experiment of at least 3 independent experiments. ^∗ p < 0.05; ^∗∗∗ p < 0.001 (comparing female to male at individual timepoints).

Figure 4

Systemic disease caused by imiquimod cream is IL-36α and IL-1R1 signaling dependent. Wild type (open bars, black circles, and lines), IL-36α ^−/− (red bars, triangles, lines, and statistics asterisks), IL-1R1^−/−(blue bars, diamonds, lines, and statistics asterisks), and IL-36α ^−/−/IL-1R1^−/− (purple bars, squares, lines, and statistics asterisks) female mice (n = 3–5 per group) were treated daily with 5% imiquimod cream (Perrigo) for 4 days. Activity (a), nest building (b), posture (c), nose bulging (d), orbital tightening (e), weight (f), food intake (g), and survival (h) were evaluated and scored as described in Table 1 and illustrated in Figure 2. ND: no disease detected, score = 0. Total disease scores (i) were calculated as the sum of individual scores for each mouse and group means (±SD) shown. ^∗ p < 0.05; ^∗∗ p < 0.01; ^∗∗∗ p < 0.001 (compared to control at individual timepoints unless indicated otherwise with black bars). Data is shown from one representative experiment of 3 independent experiments.