Heterozygous CARD9 mutation favors the development of allergic bronchopulmonary aspergillosis

Background: Previous research demonstrated that a homozygous mutation of g.136372044G>A (S12N) in caspase recruitment domain family member 9 (CARD9) is critical for producing Aspergillus fumigatus-induced (Af-induced) T helper 2 (T(H)2)-mediated responses in allergic bronchopulmonary aspergillosis (ABPA). However, it remains unclear whether the CARD9(S12N) mutation, especially the heterozygous occurrence, predisposes the host to ABPA. Methods: A total of 61 ABPA patients and 264 controls (including 156 healthy controls and 108 asthma patients) were recruited for sequencing the CARD9 locus to clarify whether patients with this heterozygous single-nucleotide polymorphisms are predisposed to the development of ABPA. A series of in vivo and in vitro experiments, such as quantitative real-time polymerase chain reaction, flow cytometry, and RNA isolation and quantification, were used to illuminate the involved mechanism of the disease. Results: The presence of the p.S12N mutation was associated with a significant risk of ABPA in ABPA patients when compared with healthy controls and asthma patients, regardless of Aspergillus sensitivity. Relative to healthy controls without relevant allergies, the mutation of p.S12N was associated with a significant risk of ABPA (OR: 2.69 and 4.17 for GA and AA genotypes, P = 0.003 and 0.029, respectively). Compared with patients with asthma, ABPA patients had a significantly higher heterozygous mutation (GA genotype), indicating that p.S12N might be a significant ABPA-susceptibility locus (aspergillus sensitized asthma: OR: 3.02, P = 0.009; aspergillus unsensitized asthma: OR: 2.94, P = 0.005). The mutant allele was preferentially expressed in ABPA patients with heterozygous CARD9(S12N), which contributes to its functional alterations to facilitate Af-induced T(H)2-mediated ABPA development. In terms of mechanism, Card9 wild-type (Card9(WT)) expression levels decreased significantly due to Af-induced decay of its messenger RNA compared to the heterozygous Card9(S12N). In addition, ABPA patients with heterozygous CARD9(S12N) had increased Af-induced interleukin-5 production. Conclusion: Our study provides the genetic evidence showing that the heterozygous mutation of CARD9(S12N), followed by allele expression imbalance of CARD9(S12N), facilitates the development of ABPA.