Summary
Thrombocytopenia is a common finding in malaria. In clinical trials, recombinant macrophage
colony-stimulating factor (M-CSF) causes a reversible, dose-dependent thrombocytopenia,
and high M-CSF has been reported in autoimmune thrombocytopenias. P-selectin, which
is secreted into the plasma following platelet/endothelial activation or damage, is
elevated in certain consumptive thrombocytopenic disorders. The relationships between
thrombocytopenia, M-CSF and P-selectin were analysed in 63 patients with severe (n
= 13) or uncomplicated (n = 26) P. falciparum (PF) or P. vivax (PV) malaria (n = 24). On admission, 69% of PF patients and 75% of PV patients were
thrombocytopenic (platelets < 150 X 109/1). M-CSF was elevated in PF (3021 ± 1844 pg/ml) and PV (2602 ± 1668 pg/ml) patients,
compared to controls (589 ± 200 pg/ml). The platelet count was inversely correlated
with M-CSF in PF (r = -0.681), and in PV malaria (r = -0.548). Elevated P-selectin
was found in severe PF malaria, but not in PV malaria. Severe PF malaria was associated
with marked thrombocytopenia, very high M-CSF, elevated P-selectin and compelling
evidence of disseminated intravascular coagulopathy (DIC). Platelet counts, M-CSF
and P-selectin returned to control values in 7-14 days. These data suggest that elevated
M-CSF in malaria, by enhancing macrophage activity, may result in increased macrophage-mediated
platelet destruction. Further, platelet/endothelial activation or damage, as measured
by P-selectin, or DIC could intensify thrombocytopenia in severe PF malaria, but does
not appear to contribute to thrombocytopenia in uncomplicated PF or PV malaria.