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Pitting of malaria parasites and spherocyte formation.

Abstract：

BACKGROUND:A high prevalence of spherocytes was detected in blood smears of children enrolled in a case control study conducted in the malaria holoendemic Lake Victoria basin. It was speculated that the spherocytes reflect intraerythrocytic removal of malarial parasites with a concurrent removal of RBC membrane through a process analogous to pitting of intraerythrocytic inclusion bodies. Pitting and re-circulation of RBCs devoid of malaria parasites could be a host mechanism for parasite clearance while minimizing the anaemia that would occur were the entire parasitized RBC removed. The prior demonstration of RBCs containing ring-infected erythrocyte surface antigen (pf 155 or RESA) but no intracellular parasites, support the idea of pitting. METHODS:An in vitro model was developed to examine the phenomenon of pitting and spherocyte formation in Plasmodium falciparum infected RBCs (iRBC) co-incubated with human macrophages. In vivo application of this model was evaluated using blood specimens from patients attending Kisumu Ditrict Hospital. RBCs were probed with anti-RESA monoclonal antibody and a DNA stain (propidium iodide). Flow cytometry and fluorescent microscopy was used to compare RBCs containing both the antigen and the parasites to those that were only RESA positive. RESULTS:Co-incubation of iRBC and tumor necrosis factor-alpha activated macrophages led to pitting (14% +/- 1.31% macrophages with engulfed trophozoites) as opposed to erythrophagocytosis (5.33% +/- 0.95%) (P < 0.01). Following the interaction, 26.9% +/- 8.1% of the RBCs were spherocytes as determined by flow cytometric reduction in eosin-5-maleimide binding which detects RBC membrane band 3. The median of patient RBCs with pitted parasites (RESA+, PI-) was more than 3 times (95,275/muL) that of RESA+, PI+ RBCs (28,365/muL) (P < 0.01). RBCs with pitted parasites showed other morphological abnormalities, including spherocyte formation. CONCLUSION:It is proposed that in malaria holoendemic areas where prevalence of asexual stage parasites approaches 100% in children, RBCs with pitted parasites are re-circulated and pitting may produce spherocytes.

journal_name

Malar J

journal_title

Malaria journal

authors

Anyona SB,Schrier SL,Gichuki CW,Waitumbi JN

doi

10.1186/1475-2875-5-64

subject

Has Abstract

pub_date

2006-07-31 00:00:00

pages

issn

1475-2875

pii

1475-2875-5-64

journal_volume

pub_type

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Pitting of malaria parasites and spherocyte formation.