Rouleaux-Forming Serum Proteins Are Involved in the Rosetting of Plasmodium falciparum-Infected Erythrocytes

Nonimmune IgM, but not IgG binds to the surface of Plasmodium falciparum-infected erythrocytes and correlates with rosetting and severe malaria.

“…To exclude the possibility that our antihuman IgG MAb reagents were of restricted specificity and we were therefore failing to detect bound IgG, we also tested a FITC-conjugated affinity-purified rabbit polyclonal antihuman IgG reagent obtained from Dako. When tested with the polyclonal reagent in a direct IFA, parasite clones/lines TM284, TM180, IT/R29, and TM284S2, which have been previously reported as binding IgG, 12,19,21 remained negative for IgG in all our experiments. We also tested the anti-human IgG MAbs in a pool and at higher concentrations (10 g/mL), and again failed to detect any evidence for IgG binding specifically to infected erythrocytes.…”

“…16 When tested with MAb reagents, we did not detect specific binding of IgG to infected erythrocytes in any of the parasite cultures examined, including the clones/lines TM284, TM180, IT/R29, and TM284S2 that have been reported previously to bind IgG. 12,19,21 We did observe very low levels of IgG, IgM, and IgA on both infected and uninfected erythrocytes in all parasite cultures and erythrocyte controls. This was seen as a faint scattering of fine dots over the cell surface (0−10 dots per cell, with 20−50% of cells showing at least one dot) that was readily visible, but difficult to reproduce photographically.…”

“…[12][13][14]21 We have studied an extensive range of laboratory clones/lines (including many previously reported as IgG positive) and field isolates using both MAbs and affinitypurified polyclonal antibodies to human IgG. Although we detected low levels of IgG binding to uninfected erythrocytes, we did not detect any evidence for specific binding of IgG to infected erythrocytes.…”

“…To assess immunoglobulin binding and to determine whether it is associated only with rosette formation as previously reported, 13,14,21 or occurs in other cytoadherent or autoagglutinating parasites, we studied 12 parasite clones/ lines of differing adhesion phenotype (Table 1). Fresh and mock-cultured uninfected erythrocytes were also studied as controls.…”

“…We have found increased amounts of IgG when parasite cultures are grown in heat-inactivated serum; however, the IgG is seen on both uninfected and infected erythrocytes. Finally, the polyclonal antibodies used to detect human IgG in previous studies [12][13][14]21 may have given false-positive results, particularly when used at high concentrations. We have found that uninfected sera from some (but not all) rabbits, sheep, and goats show surface fluorescence of infected erythrocytes in the IFA with some P. falciparum clones and field isolates.…”