The protective effect of African IgG antibodies against Plasmodium falciparum malaria
was investigated by passive transfer in Thai patients. Sera from 333 African adults
were collected in the Cote d'Ivoire and subjected to extensive screening. One hundred
fifty-three samples were discarded for safety reasons, and IgG was extracted from
those remaining under conditions allowing their use by the intravenous (iv) route.
Eight Thai patients with P. falciparum parasitemia were treated by iv inoculation
of the IgG: six with a 100 mg/kg dose given over three days, one with a single 20
mg/kg dose, and one with a single 200 mg/kg dose. To ensure a safety margin of at
least 48 hours, subjects were chosen among patients having a recrudescent parasitemia
following quinine treatment failure at the RI level. At that stage, symptoms were
mild or absent and parasitemia was low but increasing (range 4, 200-9,000/microliters).
The IgG pool exerted a profound, stage-specific, but non-sterilizing effect on each
of the strains tested, and proved to be safe. Asexual parasitemia decreased by a mean
728-fold (range 46-1,086), while gametocytes were unaffected. Clearance of parasites
and symptoms was as fast or faster than with drugs, and was consistent in the eight
patients treated, suggesting that target antigens were equally expressed in geographically
remote isolates. In peripheral blood smears, no mature forms were seen at any time
during the followup, which does not support the hypothesis that reversal of cytoadherence
occurred. After the disappearance of the transferred antibodies, recrudescent parasites
from three patients were found to be susceptible to the same extent (mean decrease
of 1,310-fold) to the same IgG preparation, indicating that selection of parasites
able to escape the effect of antibodies had not occurred. No adverse side-effects
were detected during the followup, which lasted one year.