Influence of [[alpha].sub.2]-Macroglobulin, Anti-Parasite IgM and ABO Blood Group on Rosetting in Plasmodium falciparum Clinical Isolates and Their Associations with Disease Severity in a Ghanaian Population

Purpose: The severity of Plasmodium falciparum infections is associated with the ability of the infected red blood cells to cytoadhere to host vascular endothelial surfaces and to uninfected RBCs. Host blood group antigens and two serum proteins [[alpha].sub.2]-Macroglobulin ([[alpha].sub.2]M) and IgM have been implicated in rosette formation in laboratory-adapted P. falciparum. However, there is only limited information about these phenotypes in clinical isolates. Methods: This was a hospital-based study involving children under 12 years-of-age reporting to the Hohoe Municipal Hospital with different clinical presentations of malaria. Parasite isolates were grown and rosette capabilities and characteristics were investigated by fluorescence microscopy. [[alpha].sub.2]M and IgM were detected by ELISA. Results: Rosette formation was observed in 46.8% (75/160) of the parasite isolates from all the blood groups tested. Rosettes were more prevalent (55%) among isolates from patients with severe malaria compared to isolates from patients with uncomplicated malaria (45%). Rosette prevalence was highest (30%) among patients with blood group O (30%) and B (29%), while the mean rosette frequency was higher in isolates from patients with blood group A (28.7). Rosette formation correlated negatively with age (r = -0.09, P= 0.008). Participants with severe malaria had a lower IgM concentration (3.683 [+ or -] 3.553) than those with uncomplicated malaria (5.256 [+ or -] 4.294) and the difference was significant (P= 0.0228). The mean concentrations of anti-parasite IgM measured among the clinical isolates which formed rosettes was lower (4.2 [+ or -]3.930 mg/mL), than that in the non rosetting clinical isolates (4.604 [+ or -]4.159 mg/ mL) but the difference was not significant (P=0.2733). There was no significant difference in plasma [[alpha].sub.2]M concentration between rosetting and non rosetting isolates (P=0.442). Conclusion: P. falciparum parasite rosette formation was affected by blood group type and plasma concentration of IgM. A lower IgM concentration was associated with severe malaria whilst a higher [[alpha].sub.2]M concentration was associated with uncomplicated malaria. Keywords: Plasmodium falciparum, severe malaria, uncomplicated malaria, rosettes, blood group, alpha-2 macroglobulin, immunoglobulin M