INDUCTION OF HIGH-LEVELS OF IGG AUTOANTIBODIES IN MICE INFECTED WITH PLASMODIUM-CHABAUDI

This study analyzed the effect of infection of mice with a virulent strain of Plasmodium chabaudi on natural autoantibodies. Mice received appropriate treatments in order to survive and the serum autoantibodies were characterized either by enzyme immunoassays against a panel of self and non-self antigens or by Western immunoblots using fibroblast or red blood cell (RBC) extracts. IgM and mainly IgG antibodies directed against actin, myoglobin, myosin, spectrin, tubulin, and trinitrophenylated-ovalbumin were found a few days after the parasitemia peak, persisted for several weeks after parasite clearance, and returned to almost normal levels after 2 months. Following a challenge with parasitized RBCs, a similar increase in all antibodies was observed, their levels remaining high 20 days post-injection and still remaining at twice the normal level 1 month later. Western blotting detected autoantibodies to many membrane RBC proteins, e.g. spectrin, and band 3 and its related polypeptides, as well as against fibroblast constituents, such as tubulin, actin, and the 70 kd heat shock protein. Autoantibodies seemed to be polyspecific, since those eluted from infected mouse RBCs and the IgG antibodies from infected mouse sera affinity-purified on a mouse tubulin immunoadsorbent reacted with all antigens of the panel, including parasite extracts. Suprisingly, in mice which had recovered from infection, autoantibody levels, particularly anti-spectrin and anti-band 3, rose after the injection of a high dose of normal instead of parasitized RBCs. These results suggest that the IgG autoantibodies enhanced by the P. chabaudi infection derived from natural IgG-producing clones because: (i) their rise is not preceded by an IgM peak; (ii) they are polyspecific; and (iii) they are autoregulated because their high levels are transient. In addition, our data demonstrate that cured mice become highly sensitive to a self antigen challenge.