Asthma is a chronic inflammatory lung disease which is characterized by airway inflammation, intermittent airflow obstruction, and bronchial hyper-responsiveness. Allergic asthma can be sparked by allergen sensitization in which house dust mites (HDM) are one of the most prevalent indoor allergens. The prevalence of allergic sensitization is rising in developing countries, a phenomenon related to rapid urbanization and an adult's migration from a rural to an urban area increases their risk of sensitization to mite allergens. It also could contribute to a rapid increase of chronic respiratory diseases (CRD). Exposure to dust mite allergens is a risk factor for clinical asthma in sensitized subjects.
The relationship between allergic asthma and intestinal permeability is a subject of research interest. An increase in the intestinal permeability may result in facilitating the entry of allergenic proteins from the intestinal lumen into the systemic circulation. Consequently, activation of the adaptive immune system, allergen sensitization and/or extra-intestinal inflammation occurs.
The current study is a case control study that aimed at assessing the relation between serum zonulin level as a marker of increased intestinal permeability and the severity of house dust mites allergic asthma. Our study included 96 patients; 48 asthmatic patients and 48 control subjects. The mean age of the asthmatic patients (n = 48) was 30.67 ± 15.609, 30 ( 62.5%) were females and 18 ( 37.5%) were males and most of them, 26 patients, lived in rural areas (54.16%). 39 patients (81.3%) had a positive family history of atopy. All patients displayed positive skin prick test results to house dust mites, most of the patients (70.8%) were sensitive to D. pteronyssinus and 60.4% were sensitive to D. farina. 14 patients were mono sensitized to a single type of house dust mites and 34 patients were polysensitized to both types. As for the grade of asthma severity, 4 patients (8.3%) had grade 1 severity, 24 patients (50%) had grade 2 asthma severity, 12 (25%) patients had grade 3 severity, and 8 patients (16.7%) had grade 3 asthma severity.
Several studies supported these current results indicating that bronchial asthma was associated with females with an obvious sex bias. Ricciardolo FL et al., 2020 conducted a cross-sectional study on 499 asthmatic patients to assess the potential difference between asthmatic males and females in a real-life setting. Their study also displayed a female predominance in which 301 patients 60.32% were females. In addition, Sabry, 2011 reported that 20–40% of asthmatic females of reproductive age suffer from worsening of their symptoms during their menstrual period, suggesting that sex hormones may have a major role in the biologic sex difference. .
These results could be attributed to hormonal factors, environmental exposure, and the presence of comorbidities. Since estrogen receptors (ERs) are highly expressed in the lungs and their smooth muscles with a special role in bronchoconstriction/dilatation, this explains the gender bias. Moreover, another possible hormonal factor is the lack of male sex hormone which plays an integral role in downregulation of innate and adaptive immune response. Genetic factors may also be involved. The Cyclooxygenase (COX) pathways play an important role in the course of bronchial asthma and Cyclooxygenase-2(COX-2) gene homozygosity is related to females.
In fact, rural residence has higher prevalence of parental smoking, higher number of siblings, advanced overcrowding rates, higher humidity levels and greater exposure to chemicals and farm animals. Moreover, hot climatic conditions and high population density are crucial for the development and reproduction of mites. Hence, the geographical situation of Egypt and its favorable climatic conditions together with its overpopulation contribute to the abundance of HDM especially in rural areas.
The current results displayed that asthma patients were more commonly living in rural areas (54%vs 45.84% urban asthmatics) and all of them had positive skin prick test response to house dust mites, DP;Df (70%,60% respectively). Lawson et al., 2017 likewise reported that children with asthma who lived in rural areas were more likely to wheeze or have more severe symptoms of wheeze.  Furthermore, this also agreed with Müsken et al., 2002 study which concluded that sensitization to storage mites in Germany was more frequently sensitive to D. pteronyssinus and the prevalence of positive skin test results to storage mites was greater in rural than in city dwellers. Also, In vitro sensitization to B. tjibodas mites was also significantly greater in rural than in city dwellers. Besides, Hassan and Hagrass 2017 reported that house dust mites (HDM) allergy occurs more commonly than any other allergens among Egyptian asthmatic patients. 
Several studies disclosed that the high frequency of family history of allergy is common among asthmatics. Familial assemblage of asthma and allergic disease has frequently been observed, indicating that a positive familial history of atopy may be considered as an identifiable risk factor of asthma. This may be due to the evidence hinting that genetics play an essential role in the pathogenesis of asthma. In alliance, Antonios et al. 2012 reported 60% of cases had a positive family history and displayed 95% positive reactions to both D. pteronyssinus and D. farinae allergens using SPT among asthmatic patients in Gharbia Governorate, Egypt.  Similar results were reached by Haggag MG et al, 2017.Their study revealed that 62.5% of patients had positive family history.
A detailed clinical history and physical examination followed by the detection of total serum IgE level and IgE immunoreactivity against specific allergens still represents the cornerstone in approaching allergic disorders.
On comparing serum total immunoglobulin E (IgE) level between asthmatic patients and control subjects in the present study, asthmatic patients displayed a higher statistically significant level of serum total IgE. It was statistically significantly higher among male asthmatic patients. There was a positive correlation between total serum IgE level and asthma severity grade and skin prick test results.
Several studies disclosed high serum IgE levels among asthmatic patients. This is in alliance with Kim et al. 2013 who stated that the total IgE levels were significantly higher in males. Fereidouni M et al.,2009 study uncovered that the mean total IgE serum was significantly high among asthmatics. Males had higher mean total IgE values than females (305 vs 252 IU/mL, P = 0.6), but the difference was not significant.
On the contrary, Somani ,2008 demonstrated that total IgE level is higher in female patients and they attributed their results to the possibility that total levels of IgE might be inheritable, especially in females, because of the existence of two alleles at the X-linked locus.
The disparity in the development of total IgE between males and females is the consequence of the fact that the levels of total IgE depend on many other factors; such as parasitic infestations, smoking, pollution, local diet and different genetic background in which males are at greater risk of exposure.
IgE is an antibody linked to allergic reactions and airway inflammation which is associated with asthma severity. IgE is also linked to airway hyperresponsiveness, and lower pulmonary function. Additionally, the use of monoclonal anti-IgE has resulted in decreasing asthma severity.
Concerning the correlation between level of total IgE and asthma severity, Kovač K et al,2007 also discerned that the greater the asthma severity the greater the total serum total IgE level (> 288.0 kIU/L) and specific IgE to D pteronyssinus (> 44.1 kIUA/L). They conducted a study to evaluate the correlation between serum total IgE level and asthma severity in asthmatic children sensitive to D pteronyssinus.
Kenawy et al., 2017 found a highly significant increase in serum level of IgE in patient with severe asthma than those with mild asthma with P values < 0.001. Likewise, a study done by Rotsides and his coworkers (2010) reported a strong positive association between high IgE level and asthma severity in children and they proposed that serum IgE level is a strong predictor for allergy in asthmatic children. 
Regarding the relation between serum IgE level and the positivity of skin prick test, Baldacci S et al., 1996 concluded that the higher IgE levels the greater the positivity of SPT regardless the gender . Rose et al., 1996 likewise assumed that there is some inverse relationship between the quantitative level of IgE antibody and the level of allergen necessary to cause symptoms of asthma.
The impairment of the epithelial barrier is a corner stone in the development of allergic diseases. Increased intestinal permeability, either due to the exposure to antigens in asthmatic patients or due to a barrier defect, play a critical role in susceptibility to environmental allergens. The process responsible for enhanced intestinal permeability in asthma is still indeterminate. There is an association between enhanced intestinal permeability and the severity of the asthma, airflow obstruction, which suggests that it is a bronchus to gut disease.  This could be attributed to the fact that mucosal defects can exist simultaneously in a lot organs and antigenic stimulation as well as environmental factors can result in its clinal expression in a single organ. . For instance, identical histological mucosal changes have been observed in both duodenal and bronchial mucosa simultaneously.
Therefore, correction of the gastrointestinal barrier defect is possibly an additional alternative approach for asthma treatment [34–36]. As it leads to reduction of epithelial liability to damage and resultant inflammatory and remodeling reaction. In addition to growth factors, several peptides can repair barrier function for example AT-1001, a peptide inhibitor of zonulin . It is therefore essential to study serum zonulin level and its regulation in patients with asthma.
The present study disclosed that asthmatic patients displayed a higher statistically significant level of serum zonulin than control subjects. Patients living in rural areas had a significantly higher level on serum zonulin. Furthermore, there was a significant correlation between zonulin level and asthma grade. The higher the zonulin level the greater the grade of asthma severity. Nevertheless, we found that there was no difference in serum levels of zonulin subjects regarding gender and age. The cut of value of serum zonulin level to differentiate between grade 1–2 asthma severity and grade 3–4 asthma severity. In addition, serum zonulin showed a sensitivity equal to 80%, a specificity equal to 71.4%, a positive predictive value equal to 66.7% and a negative predictive value equal to 83.3%. There was no statistically significant correlation to serum total IgE concentration. Grade of asthma had independent significant effect on zonulin level while serum total IgE had no significant effect on zonulin level via linear regression analysis.
A study conducted by Benard and colleagues to assess the intestinal permeability in asthmatics via administering oral radioactive CrEDTA and estimating its urinary recovery revealed that asthmatic patients had increased intestinal permeability in comparison. Unlike the current results, it was not correlated to the severity of asthma as deduced by pulmonary function test measurements or to the use of steroid treatment  This may be due to the difference in the method used to assess intestinal permeability.
Furthermore, a study performed by Cervantes-García D and collaborators aiming at assessing the outcome of oral Lactococcus lactis NZ9000 use on airway inflammation and lung remodeling in asthmatic rats and its relation to the preservation of the intestinal barrier, concluded that oral L. lactis could be used for asthma prevention through its maintenance of an adequately functioning intestinal barrier.
Initial findings imply that a group of asthmatic patients has both high levels of serum zonulin and enhanced intestinal permeability . These findings indicate that antigens presentation and subsequent lung inflammation occur as result of passage of antigens through lung and intestinal mucosa and submucosa and later stimulate the immune system resulting in lung inflammation .
Moreover, a study performed by Yamaide F et al. 2020 to examine the differences between serum zonulin level among allergic children and non- allergic children concluded that serum zonulin was significantly greater in children with allergy (Food allergy, Bronchial Asthma). In addition, it was significantly higher in patients with food allergy than in bronchial asthma patients. However, their results are not completely reliable as food allergy can be the main reason for increased intestinal permeability and this explains the higher increase in zonulin level among food allergy patients than among asthmatic ones. 
Up to the present moment no studies have been conducted to assess the relationship between serum zonulin level and asthma severity or to assess its correlation to different residential distribution. A study performed by Sheen et al to assess serum zonulin level in atopic dermatitis (AD) and its correlation to disease severity. They found that AD group had a greater median serum zonulin level than the control group and serum zonulin level had significantly positive correlations with age and the SCORAD index, but not with total IgE, total eosinophil count (TEC), or the number of allergens to which a child is sensitized. And concluded that each 1 ng/mL increase in serum zonulin was associated with a 15% greater risk of moderate-severe AD . Their results agree with the current results as regards the correlation between serum zonulin level and total serum IgE level. Both revealed no statistically significant correlation.