PF4 and Hermansky-Pudlak syndrome: With regards to anti-angiogenic growth factors, our data showed that the TSP-1 and PF-4 levels in HPP were comparable to fresh plasma at all incubation time points, and were significantly lower than in HPS, indicating that hypoxic conditioning itself did not promote TSP-1/PF-4 expression, but rather platelet activation was the main source of these angiogenic inhibitors in these secretomes (Figure 3A,B).