This set represents Class 1A PI3Ks including all three genes that can give rise to the five isoforms of the regulatory subunit. Note that the p85 alpha form is almost always the form used as a reagent experimentally and measured by p85-Abs.The other forms are rarely used or determined experimentally. Also note that Class 1A PI3Ks may not be the most relevant physiologically in some cell types (e.g. T cells). There are five variants of the p85 regulatory subunit, designated p85alpha, p55alpha, p50alpha, p85beta, and p55gamma. There are also three variants of the p110 catalytic subunit designated p110alpha, beta, or gamma catalytic subunit. The first three regulatory subunits are all splice variants of the same gene (Pik3r1), the other two are expressed by Pik3r2 and Pik3r3, respectively). The most highly expressed regulatory subunit is p85alpha. All three catalytic subunits are expressed by separate genes (Pik3ca, Pik3cb, and Pik3cd for p110alpha, p110beta and p110gamma, respectively). The alpha and beta p110s are expressed in all cells, while p110gamma is expressed primarily in leukocytes. It has been suggested that it evolved in parallel with the adaptive immune system. The regulatory p101 and catalytic p110gamma subunits comprise the class IB PI3Ks, each is encoded by a single gene.