This paper describes changes in the circulating platelets of 25 patients with acute malaria within 2 to 6 days of onset of illness. Thrombocytopenia was observed in 10 out of 15 patients with Plasmodium falciparum infection, and in 4 out of 9 patients with P. vivax infection. One patient with a mixed infection of both species had a disseminated intravascular coagulation. Platelet antibody was detected in the sera of 8 out of 11 cases by the complement lysis inhibition technique and indirect immunofluorescence. The mean platelet antibody concentrations in the sera of 11 patients and 53 control subjects were 122.70 +/- 80.25 ng/10(7) platelets and 36.69 +/- 18.72 ng/10(7) platelets, respectively. An inverse relationship between the platelet count and platelet antibody levels in serum supported the view that thrombocytopenia in malaria may be partly immune-mediated. Platelet aggregation responses to agonists such as ADP, adrenaline, collagen and ristocetin revealed hyperactivity. Ultrastructural study of unstimulated platelets from patients revealed several changes such as centralization of dense granules, glycogen depletion, and formation of pseudopods and microaggregates, indicating in vivo activation of the platelets, which may also lead to thrombocytopenia.

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Summary Cultures of lymphocytes with and without phytohaemagglutinin (PHA) were used as an in vitro model system to study the cellular uptake of tritiated folic acid, [3H]PteGlu and of14C labelled 5 methyltetrahydrofolic acid, 5 [methyl‐14C]‐H4PteGlu. Total folate uptake by PHA‐stimulated transformed lymphocytes, measured both by liquid scintillation counting and by autoradiography, was much greater than by non‐stimulated mature lymphocytes. This suggests that growing and dividing cells take up folate more avidly than mature non‐dividing cells. Uptake of both folate compounds, measured over a 4 hr period, was (a) approximately 80% less at 4°C than at 37°C, (b) exhibited saturation kinetics, and (c) was inhibited by methotrexate in concentrations of 10−3 M, 10−4 M, but was not affected by methotrexate at a concentration of 10−6 M. The results suggest that an active transport mechanism may be at least partly involved in cellular folate uptake. The two folate compounds, PteGlu and 5 methyl H4PteGlu, however, do not appear to share the same uptake pathway, since PteGlu did not inhibit the uptake of 5 [methyl‐14C]H4PteGlu by PHA‐stimulated lymphocytes. Further, the uptake of 5 [methyl‐14C]H4PteGlu by PHA‐stimulated lymphocytes from six patients with untreated pernicious anaemia was found to be significantly impaired, whereas the uptake of [3H]PteGlu by those cells was normal. Diphenylhydantoin did not show any consistent effect on folate uptake by lymphocytes. A sequential relation was found between the peak rates of RNA synthesis, folate uptake and DNA synthesis by PHA‐stimulated lymphocytes. The peak rate of folate uptake occurred at 44–48 hr of culture, and preceded peak DNA synthesis by 24 hr and followed peak RNA synthesis by 24 hr. Folate uptake, however, did not appear to be directly coupled to either DNA or RNA synthesis, since actinomycin D inhibited both DNA and RNA synthesis by transformed lymphocytes over a 4 hr period without significantly affecting folate uptake.