Activated PI3K Delta Syndrome-1 mutations cause neutrophilia in zebrafish larvae.

People with Activated PI3 Kinase Delta Syndrome 1 (APDS1) suffer from immune deficiency and severe bronchiectasis. APDS1 is caused by dominant activating mutations of the PIK3CD gene that encodes the PI3 kinase delta (PI3Kδ) catalytic subunit. Despite the importance of innate immunity defects in bronchiectasis, there has been limited investigation of neutrophils or macrophages in APDS1 patients or mouse models. Zebrafish embryos provide an ideal system to study neutrophils and macrophages. Previous studies of zebrafish with strongly hyperactivated PI3 kinase activity due to Pten deficiency, revealed excessive production of immature neutrophils that fail to mature. We used CRISPR-Cas9 and CRISPR-Cpf1, with oligo-nucleotide directed homologous repair, to engineer zebrafish equivalents of the two most prevalent human APDS1 disease mutations. These zebrafish pik3cd alleles dominantly cause excessive neutrophilic inflammation in a tail-fin injury model. They also exhibit total body neutrophilia in the absence of any inflammatory stimulus but have normal numbers of macrophages. Exposure to the PI3Kδ inhibitor CAL-101 reverses the total body neutrophilia. There is no apparent defect in neutrophil maturation or migration and tail-fin regeneration is unimpaired.