IL13 and asthma: It is suggested that the single change in the nucleotide sequence of the IL-13 gene substitutes the arginine amino acid with glutamine, increasing the receptor binding affinity of the secreted cytokine which ultimately increases the downstream inflammatory activity [40] Imraish et al., however, report a significant reduction in IgE serum levels in asthmatics carrying the minor allele of the rs20541, suggesting an inverse relationship between this SNP and the severity of asthma [41].