In vitro, Plasmodium falciparum infected erythrocytes (IE) may show rosette formation, the adherence of 22 uninfected erythrocytes to an ervthrocvte containing a mature-stage parasite. Rosette fokatio-n has been a&ociated with severity of malarial disease in African children in some studies (CARLSON et al., 1990;ROWE et al., 1995) but not all (ROGERSON et al., 1999). Most laboratory lines of I? falcipancm have been reported to require human serum for rosette formation (CLOUGH et al., 1998;TREUTIGER et al., 1999) but this requirement has not been demonstrated for patient isolates. Patient isolates gtow as well in fetal calf serum or Albumax II as in AB serum, a measure which reduces costs and increases convenience of culture. We have examined patient isolates for dependence on human serum for rosette formation.
Venous blood was collected from 26 children with cerebral malaria and/or severe malaria anaemia attending the Queen Elizabeth Central Hospital, Blantyre, Malawi, after informed consent was obtained from each patient's guardian. Samples were washed and cultured as described previously (ROGERSON et al., 1999) in culture medium supplemented with either 10% non-immune human AI3 serum v/v or 0.5% Albumax II [Gibco BRL, Grand Island, NY, USA] w/v (CRANMER et al., 1997). Trophozoite-stage IE were stained with acridine orange and examined by fluorescence microscopy for rosette formation. Each sample was examined in duplicate, and at least 200 IE were assessed for each duplicate. Rosettes (IE with at least 2 uninfected erythrocytes adherent) are reported as percentage of all trophozoite-containing IE in rosettes.
Parasite growth rates were identical in cultures supulemented with 10% AB serum or 05% Albumax II tdata not shown). There were significantly lower rates of rosette formation in Albumax II (median O-2, range O-5% rosetting) than in AB serum (median 2.2, range O-29.3%). Ten of 26 isolates formed no rosettes in Albun& II and 12 others formed < 1% rosettes, whereas only 2 of 26 isolates in AB serum failed to rosette (Figure ) and 5 formed 5% rosettes in AB serum, rosetting was decreased by 85-100% by culture in Albumax II. Rosetting in Albumax II was never >I% greater than that in AB serum.
When patient isolates of I? falciparum were cultured in medium containing 0.5% Albumax II or in human AB serum (CRANMER et al., 1997) most but not all formed more rosettes in human serum. We did not examine