Date Published: December 14, 2011
Publisher: BioMed Central
Author(s): Narcy G Arizmendi, Melanie Abel, Lakshmi Puttagunta, Muhammad Asaduzzaman, Courtney Davidson, Khalil Karimi, Paul Forsythe, Harissios Vliagoftis.
Allergic sensitization to aeroallergens develops in response to mucosal exposure to these allergens. Allergic sensitization may lead to the development of asthma, which is characterized by chronic airway inflammation. The objective of this study is to describe in detail a model of mucosal exposure to cockroach allergens in the absence of an exogenous adjuvant.
Cockroach extract (CE) was administered to mice intranasally (i.n.) daily for 5 days, and 5 days later mice were challenged with CE for 4 consecutive days. A second group received CE i.n. for 3 weeks. Airway hyperresponsiveness (AHR) was assessed 24 h after the last allergen exposure. Allergic airway inflammation was assessed by BAL and lung histology 48 h after the last allergen exposure. Antigen-specific antibodies were assessed in serum. Lungs were excised from mice from measurement of cytokines and chemokines in whole lung lysate.
Mucosal exposure of Balb/c mice to cockroach extract induced airway eosinophilic inflammation, AHR and cockroach-specific IgG1; however, AHR to methacholine was absent in the long term group. Lung histology showed patchy, multicentric damage with inflammatory infiltrates at the airways in both groups. Lungs from mice from the short term group showed increased IL-4, CCL11, CXCL1 and CCL2 protein levels. IL4 and CXCL1 were also increased in the BAL of cockroach-sensitized mice in the short-term protocol.
Mucosal exposure to cockroach extract in the absence of adjuvant induces allergic airway sensitization characterized by AHR, the presence of Th2 cytokines in the lung and eosinophils in the airways.
Atopy and allergic diseases affect more than 30% of the population worldwide. A study in 10 European countries showed that if we only take into account respiratory allergic conditions they still have a prevalence between 11.7% and 36.6% . The economic burden of these diseases is also very high . Despite intense efforts over the last 3 decades, the mechanisms controlling the development of allergic sensitization are still poorly understood. Animal models have been shown to be invaluable in allowing us to understand the pathogenesis of allergic conditions, especially asthma.
We have developed a model for mucosal sensitization of mice using whole body cockroach extract. Groups of mice received 50 μg of CE intranasally after anesthesia on 5 consecutive days, rested for 5 days and then received 50 μg of CE intranasally daily for 4 more days. Airway hyperresponsiveness (AHR) was assessed 24 h after the last allergen exposure and allergic airway inflammation was assessed 48 h after the last allergen exposure using BAL and lung histology (Figure 1A – short term protocol). To extend the duration of exposure to allergen we sensitized another group of mice with 50 μg of CE intranasally 5 days a week for 3 weeks, and for 2 consecutive days on the fourth week before evaluation for AHR and allergic airway inflammation as before (Figure 1A – long term protocol). Control groups of mice received saline on the same schedule. To compare our models with better-established models of parenteral sensitization in the presence of an adjuvant, a group of mice were sensitized with CE extract and Al(OH)3 i.p. and then challenged with CE i.n. (Figure 1A – i.p.).
In this manuscript we present a detailed analysis of the airway inflammation present in a model of mucosal sensitization to cockroach allergens. Mice sensitized to cockroach through the intranasal route in the absence of an adjuvant developed all the expected characteristics of asthma; they developed AHR, eosinophilic airway inflammation and allergen-specific IgG1 antibodies after exposure to allergens over a period of 2 weeks. These mice also showed increased levels of Th2 cytokines and a number of chemokines in the lung tissue. Mucosal exposure to CE led to allergic inflammation in both Balb/c and C57Bl/6 mice, although the latter had lower numbers of eosinophils accumulating in the airways. Mice exposed to CE for longer periods, 17 intranasal exposures over 31/2 weeks, showed lower AHR and less eosinophils in the BAL compared to mice treated with the short term model. Histological evaluation of the short and long term models showed changes compatible with allergic airway inflammation. The changes seen in the lungs stained with H&E were quite mild compared to other murine models of asthma. CE induced inflammation in both the short and long term models compared to non-sensitized mice. The inflammation seen in the long term model was more diffuse with smaller aggregates of inflammatory cells than what was seen in the short term model. PAS-D staining of the lungs of CE sensitized and challenged mice showed increased goblet cells in the airways in both models compared to non-sensitized mice. The exact reason for decreased levels of inflammation in the long term protocol are not known. Other groups using various models have shown that longer exposure to allergens can lead to tolerance and therefore have decreased levels of inflammation compared to the allergic inflammation seen following shorter exposure periods [10,11]. It is possible that a similar effect is seen in our model.
In conclusion, we have presented a detailed analysis of a model of allergic sensitization using mucosal exposure to cockroach allergens, which is functional in both Balb/c and C57Bl/6 mice. This model may allow us to better understand the role of cockroach allergens in allergic disease and in the inner city asthma epidemic.
AHR: airway hyperresponsiveness; BAL: bronchoalveolar lavage; CE: cockroach extract; H&E: hematoxylin and eosin; i.n.: intranasal; i.p.: intraperitoneal; PAS-D: periodic acid shift with diastase
The authors declare that they have no competing interests.
NGA carried out most of the animal studies, participated in the study design and drafted the manuscript. MA carried out animal studies and participated in the study design. LP performed all histological analysis and prepared the histological pictures. MA performed the cytokine/chemokine analysis. CD participated in the studies analyzing airway inflammation and helped draft the manuscript. KK performed the flow cytometry studies and contributed in study design. PF participated in the study design and helped draft the manuscript. HV participated in the study design and helped draft the manuscript. All authors read and approved the final manuscript.