The association of MUC5AC with bronchitis is only significant in individuals who lack the IL1RN*2 (risk) allele (Fig. S2A in the supporting information available online) and only in individuals homozygous for the ERBB1 common rs2227983(R) allele—that is non-carriers of the rarer K allele (Fig. S2B in the supporting information available online). This evidence concerns the gene IL1RN and bronchitis.