In the last decade, several studies have shown that the receptor for beta 2 agonist is intimately connected, physically and functionally, to the CFTR protein on the surface of the epithelial cells in the airways . Interestingly, the function of this complex behaves differently if the stimulus is caused by long or short term beta 2 agonist substances [20–22]. The clinical response of the CF patients in relation to the long-term beta agonists in the different polymorphisms in ADRB2 gene has not been studied, while for the short term use, there are few studies in the literature [17–19]. With asthma, the Arg16Gly and Gln27Glu polymorphisms in ADRB2 gene cause different reactions to the Bronchodilation promoted by BD ; however, little is known about their impact on the severity and response to Bronchodilation caused by CF BD [17–19].
To the best of our knowledge it is known that the allele frequency for the Arg16Gly and Gln27Glu polymorphisms in ADRB2 gene is different in adults and children with CF . Adult patients with CF have a higher frequency for the Gly16 and Glu27 alleles compared to people CF free. Children with CF have a lower frequency for Gly16 and similar with the Glu27. Young adults with CF in relation to the variant forms in ADRB2 gene did not differ from the population in general. In our population there was no difference in genotype distribution for the Arg16Gly (p:0.92) and Gln27Glu (p:0.88) polymorphisms in ADRB2 gene relative to the patients' age group.
Our study showed an association of the Arg16Gly polymorphism in ADRB2 gene with the severity of CF markers. The variation in the spirometry proof before and after the use of BD was associated with the Arg16Gly and Gln27Glu polymorphisms in ADRB2 gene. Twenty six of CF´s severity markers were used in the study; and the response to Bronchodilation was assessed by four spirometry markers.
Hart et al. (2005)  used the FEV1(%) and the FEF25-75% as severity markers, in addition to the following variables adjustment: age, gender, the F508del homozygous and Pseudomonas aeruginosa status. Buscher et al. (2002)  used the following markers: FEV1, FVC, flow at lower lung volumes (MEF50%VC), measurement of cAMP accumulation in intact mononuclear lymphocytes, age, gender, BMI, F508del homozygous and Pseudomonas aeruginosa status. Hart et al. (2005)  considered the presence of values 12% higher in the FEV1 after using the BD, (the examination of spirometry occurred 15 minutes after administration of BD), a positive response to Bronchodilation, while Buscher et al. (2002)  believed in the 10% variation for the same marker (the Spirometry test occurred 5 minutes after BD administration). Steagall et al. (2007)  used as markers: age, sex, F508del status, carbon monoxide diffusing capacity (DLCO), FEV1(%) and the FVC(%). The positive response to Bronchodilation was seen as a positive variation superior to 12% for the FEV1 and the FVC spirometry markers.
The presence of different genotypes in the analyzed mutations, (belonging to the classes I, II and/or III), of the CFTR gene, along with the polymorphisms in ADRB2 gene were associated to different markers related to CF´s severity.
An intriguing aspect of our study, not previously described, were the findings that CF´s patients with two mutations from classes I, II and/or III, Arg/Arg homozygous for the Arg16Gly polymorphism, have greater impairment of lung function than the Gly/Gly homozygous, provided by the Bhalla score. And the Gly/Gly homozygous showed higher pancreatic insufficiency than the Arg/Arg. The two clinical variables are associated with CF severity, and are modulated by the Gly/Gly genotype to Arg16Gly polymorphism in our population. The Gly allele is associated with fast protein degradation  that was identified as a severity factor.
The first isolation of the P. aeruginosa was confirmed later in patients with the Gly/Gly genotype and two mutations classes I, II and/or III in CFTR gene. The early colonization is associated with clinical deterioration and a greater degree of airway inflammation .
The response to this polymorphism and the clinical aspects of CF´s patients has not been studied in the literature referenced, except for Buscher et al., (2002) , whose analysis of some of the markers, (age, gender, BMI and P. aeruginosa status), showed no significant association, a fact that hampered data comparison. Another relevant fact is the Gln27Glu polymorphism lack of association with severity markers in the study. There were no references in the scientific literature indicating this polymorphism as a modulator of CF´s severity.
Our results show that CF´s patients with the Arg/Arg genotype from the Arg16Gly polymorphism have lower values of the FEV1 and FEF25-75%. The observation contrasts with the data from Buscher et al. (2002)  who reported higher values of the Arg/Arg genotype in 87 CF´s patients for the FEV1, FVC, and MEF50%VC markers, when compared with subjects with a genotype containing at least one Gly allele. The same was observed when the genotype for the delF508 mutation was used; 51 patients were analyzed, and higher values for the markers were found for the same genotype.
In our data the Gln27Glu polymorphism in ADRB2 gene was not associated with spirometry markers. Diversely, in the Buscher et al. (2002)  study, the Gln/Gln genotype for the Gln27Glu polymorphism, when compared with the others, showed a higher correlation for the FEV1, FVC, and MEF50%VC values. In the Steagall et al. (2007)  study there was no correlation between the DLCO, FEV1 and the FVC in patients with homozygous F508del stratified by the Arg16Gly and Gln27Glu polymorphisms genotype in ADRB2 gene.
The patients with no identified mutations in CFTR gene, in our study, showed higher values in the FEF25-75% for the Gly/Gly genotype. Thus, comparing the data discussed above, we denote the influence of the Arg16Gly polymorphism in ADRB2 gene that occurs in the spirometry, and that is also influenced by the genotype in the CFTR gene.
We found that the Arg27Gly polymorphism in ADRB2 gene was associated with the bronchospasm response mediated by beta 2 agonists. The FEV1(%) variation was lower in patients with the Gly/Gly genotype, when compared with the Arg/Arg and Arg/Gly genotypes. The FEF25-75% was lower in patients with the Gly/Gly genotype when compared to the Arg/Arg and Arg/Gly. Patients with the Arg/Arg genotype showed higher FEF25-75% when compared to the Arg/Gly genotype.
In the study by Hart et al. (2005) , one hundred and six patients with CF underwent spirometry before and after the BD administration, and the Arg16Gly and Gln27Glu polymorphisms genotype was determined. The positive response was observed in 15% (23/154) of the included patients and 17% (18/106) among the patients who had genotype for the gene ADBR2 determined. There was no significant relationship between the ADRB2 gene genotype for the Arg16Gly and Gln27Glu polymorphisms and the response to the BD . However, after the FEV1 adjustment in percentage for the predicted and the status of infection by the P. aeruginosa, a significant difference occurred to the FEF25-75% percentage of change (4.9%, 18.0% and 22.4% for the genotypes AA, AG and GG; respectively). The FEF25-75% percentage of change showed no substantial difference for the codon 27, even after the adjustment for the infection by P. aeruginosa and by the predicted baseline of FEV1(%) . After adjusting the FEV1 percentage predicted baseline, the codon 27 groups differed significantly from the percentage of change in the FEV1(%) (4.1%, 8.1% and 9.3% for the genotypes CC, CG and GG; respectively) . The authors suggested that the effect of the two polymorphisms were complex and the haplotype analysis may be more informative than any genotype alone . To that effect, a large number of patients would be needed, only possible in multi-centric studies. Then again, in multi-centric studies the environment and diverse management systems could provide significant bias in the clinical severity outcome.
In the study by Buscher et al. (2002) , no statistically significant difference was found for the FEV1 average value and in the absolute number of patients with positive response to BD among the Arg16Gly polymorphism genotypes in ADRB2 gene.
In the Steagall et al. (2007)  study homozygous patients with the delF508 mutation were analyzed for their reactions to Bronchodilation. Patients who showed no response to the Bronchodilation had, on average, higher values in the FVC and FEV1 for the Arg/Arg genotype in the Arg16Gly polymorphism of the ADRB2 gene when compared to other genotypes; however, in the analyzed group there were only two patients with the Arg/Arg and two with the delF508 mutations for the CFTR gene. For the Gln27Glu polymorphism, the Gln/Gln genotype was associated with higher FVC values. In the responders group only the Gln27Glu polymorphism was associated with higher values of the DLCO, FVC and FEV1 for the Gln/Glu genotype. In our study, the distribution of responders and non-responders to the pulmonary function test with the BD use, and the distribution by the polymorphisms in ADRB2 gene and mutations in classes I, II and/or III, was performed, but the sample power was less than 80%.
The long term decline in spirometry values was not evaluated in this study, even though it presents a promising field of study, verified by Buscher et al. (2002)  who demonstrated that, in 59 CF patients aged 6-20 years, the biggest FEV1 decline was in patients with at least one Gly allele, while no change in pulmonary function was seen in patients homozygous for Arg.
The genic interaction analysis performed by the MDR 2.0 program showed a combination of both polymorphisms with the variation for the FEF25-75% but not to other markers of severity. Thus, this corroborates that the polymorphisms in ADRB2 gene influence the Bronchodilation response.
In the haplotypes analysis the Ar/Arg + Gln/Gln presence was associated with the best response to Bronchodilation for the marker FEV1/FVC (N = 56; +4.61% ± 10.45), when compared to the other groups: 1 GG [Arg/Arg + Glu/Glu, Arg/Gly + Glu/Glu, Gly/Gly + Gln/Gln, Gly/Gly + Gln/Glu (N = 34; +0.53% ± 7.75)] and 2 GG [Gly/Gly + Glu/Glu (N = 4; -2.25% ± 9.605)]. In the study by Hart et al. (2005) , the haplotypes analysis for three different models demonstrated association with the FEV1 marker. And the values of 4.4 (± 5.8), 7.9 (± 8.7) and 9.0 (± 5.8); respectively to 0 GG (N = 27), 1GG (N = 64) and 2GG (N = 15), with p values equal to 0.033, 0.027 and 0.305; respectively for the models, additive, dominant and recessive.
In our results, the bronchodilator response was reduced with the presence of the variants with Gly or Glu allele, a fact contrary to that reported by Hart et al. (2005) .
Possible limitations of our study included: sample size, different age groups, and different severities of lung disease that could express differences in the BD response.
Our data can provide better understanding about the association between polymorphism associated with β2-AR protein and the clinical markers of CF´s severity, and others studies about the large macromolecular complex are necessary to improve knowledge about the interaction of the proteins on the bronchial epithelial surface.