Autoantibodies to red blood cells in rats infected with Plasmodium berghei.

A radio-iodinated Protein A (125SPA) binding assay was used to identify autoantibodies to red blood cells (RBC's) in sera of rats infected with Plasmodium berghei. Sera taken from rats at various times after infection were reacted with washed, normal RBC's, then the RBC's were washed and treated with 125SPA. The bound radioactivity was taken as a measure of the amount of Ig attached to the RBC's membranes. Using this test, anti-RBC autoantibodies were detected in rat sera as early as 5 days after infection. The level of the autoantibodies rose to a maximum at 12 to 14 days, at which time parasitemia was also maximal, then declined sharply. Autoantibodies were still detectable at 21 days after infection. Red blood cells from infected rats had readily detectable, membrane-bound Ig, as shown by their capacity to bind 125SPA directly. The amount of this Ig rose and fell in a fashion closely paralleling course of parasitemia.