PF4 and Hermansky-Pudlak syndrome: In the first step of characterizing growth factors in porcine HPS, we quantitively analyzed the concentration of three pro-angiogenic (VEGF-A, PDGF-BB, and bFGF) and two anti-angiogenic (TSP-1 and PF-4) growth factors in comparison to normal serum (NS) (Figure 2A,B).