KIT and mastocytosis: The authors further assessed PD-1 expression within cultured mast cell lines by flow cytometry and reverse-transcriptase polymerase chain reaction (RT-PCR), demonstrating PD-1 mRNA within the LAD2 cell line, a human mastocytosis cell line with wildtype KIT, while no PD-1 mRNA was detected within the HMC1.2 cell line, a human mastocytosis cell line with V560G and D816V KIT mutations.