REDUCED MICROBICIDAL AND ANTITUMOR ACTIVITIES, OF HUMAN MONOCYTES AFTER INGESTION OF PLASMODIUM-FALCIPARUM-INFECTED RED-BLOOD-CELLS

Oxidatively stressed red blood cells (RBC) and Plasmodium falciparum-i nfected RBC (PRBC) are avidly phagocytosed by human peripheral monocyt es. Following the ingestion of PRBC the monocytes' ability to phagocyt ose PRBC and to generate aggressive oxidative compounds is severely im paired. In the present work the microbicidal and anti-tumour capacitie s of monocytes fed with diamide-treated RBC and PRBC harbouring mature (trophozoite) parasites have been investigated. The capacity, of the latter, but not of the former, to phagocytose Escherichia coli and Sta phylococcus aureus and to kill them, as well as ingested Candida albic ans cells intracellularly, was found to be markedly impaired. Monocyte s that have ingested PRBC had a significantly reduced cytostatic and c ytolytic activities against a lymphoblastic tumour cell line. Monocyte s fed with oxidatively stressed RBC had normal or sometimes even great er anti-tumour activities. Monocytes that have ingested PRBC showed a reduced capability to produce superoxide following stimulation with ph orbol ester. Such impairment in monocyte functions may explain the red uced antibacterial and anti-tumour activities of monocytes in malaria patients, and could be consequential to their ability to resist bacter ial infections and to provide means for the control of tumour developm ent in those patients.