IL-13 Induces Disease-Promoting Type 2 Cytokines, Alternatively Activated Macrophages and Allergic Inflammation during Pulmonary Infection of Mice with Cryptococcus neoformans

Abstract

In the murine model of Cryptococcus neoformans infection Th1 (IL-12/IFN-γ) and Th17 (IL-23/IL-17) responses are associated with protection, whereas an IL-4-dependent Th2 response exacerbates disease. To investigate the role of the Th2 cytokine IL-13 during pulmonary infection with C. neoformans, IL-13-overexpressing transgenic (IL-13Tg+), IL-13-deficient (IL-13−/−), and wild-type (WT) mice were infected intranasally. Susceptibility to C. neoformans infection was found when IL-13 was induced in WT mice or overproduced in IL-13Tg+ mice. Infected IL-13Tg+ mice had a reduced survival time and higher pulmonary fungal load as compared with WT mice. In contrast, infected IL-13−/− mice were resistant and 89% of these mice survived the entire period of the experiment. Ag-specific production of IL-13 by susceptible WT and IL-13Tg+ mice was associated with a significant type 2 cytokine shift but only minor changes in IFN-γ production. Consistent with enhanced type 2 cytokine production, high levels of serum IgE and low ratios of serum IgG2a/IgG1 were detected in susceptible WT and IL-13Tg+ mice. Interestingly, expression of IL-13 by susceptible WT and IL-13Tg+ mice was associated with reduced IL-17 production. IL-13 was found to induce formation of alternatively activated macrophages expressing arginase-1, macrophage mannose receptor (CD206), and YM1. In addition, IL-13 production led to lung eosinophilia, goblet cell metaplasia and elevated mucus production, and enhanced airway hyperreactivity. This indicates that IL-13 contributes to fatal allergic inflammation during C. neoformans infection.

Eosinophils Contribute to IL-4 Production and Shape the T-Helper Cytokine Profile and Inflammatory Response in Pulmonary Cryptococcosis

“…11 For determination of C. neoformans-specific serum IgE, the following capture ELISA was developed. ELISA plates (Nunc GmbH & Co KG, Langenselbold, Germany) were coated with 5 g/mL ratanti-mouse IgE mAb (R35-72; BD Biosciences) in carbonate buffer (pH 9.5) overnight at 4°C.…”

“…7,11 BALB/c WT mice infected i.n. with only 500 CFUs of C. neoformans strain 1841 show dissemination from lung to brain beginning at approximately 6 weeks after infection (data not shown), leading to death 10 weeks after infection.…”

“…with only 500 CFUs of C. neoformans strain 1841 show dissemination from lung to brain beginning at approximately 6 weeks after infection (data not shown), leading to death 10 weeks after infection. 7,11 This pulmonary cryptococcosis model is a long-term model compared with other published murine models. 8,[23][24][25][26][27] To monitor IL-4 production over time in this long-term model, IL-4 reporter mice, termed 4get mice, were infected, and enhanced green fluorescent protein (eGFP) expression, which is known to correlate with IL-4 transcription, was assessed.…”

“…Whereas IL-12-dependent Th1 responses are protective, with an additional contribution by IL-23-dependent Th17 responses, [7][8][9] Th2 cells producing IL-4, IL-13, and IL-5 are detrimental. 10,11 Studies 12-14 that used i.v. inoculation examined the traversal of the blood-brain barrier by C. neoformans and led to the conclusion that transmigration can occur with intracellular and extracellular fungi.…”

“…5 In addition, IL-13-dependent mucus production by goblet cells, IL-4 -dependent IgE production, IL-5-dependent eosinophilia, and functional pulmonary impairment can be found; these features are also typically described in asthma. 16 -18 Studies 10,11,19 of pulmonary and cerebral cryptococcosis in IL-4 -, IL-13-, IL-4 receptor ␣-, and IL-4/IL-13-deficient mice or mice treated with anti-IL-5 convincingly provide a basis for future immunotherapies by targeting one or several of these Th2-associated molecules. However, it is unclear when IL-4 production starts after pulmonary infection.…”