PIK3CD and chronic obstructive pulmonary disease: Class I PI3K is a heterodimer composed of a regulatory subunit (p85) and a catalytic subunit (p110).247 There are four types of catalytic subunits: p110α, p110β, p110δ and p110γ, and while δ and γ subunits are limited to white blood cells, α and β subunits are widely distributed in various cells.248 PI3K, especially PI3K δ and γ subtypes, are closely related to a COPD inflammation.