C3b inactivator in normal mice and mice infected with Plasmodium berghei berghei.

C3b inactivator levels were assayed in clean albino mice and mice infected with Plasmodium berghei berghei. Infected animals (63.1%) had low C3b inactivator levels when compared with 45% of controls with low levels. In the low titre range, infected mice had a significantly lower mean level (P less than 0.001) of the factor than controls. Conversely, in the high titre range, the mean C3b inactivator level is significantly (P less than 0.001) higher in infected than in control mice. Lower levels of the protein were associated with low grade parasitaemia, while raised levels were found in animals with higher parasitaemia. Low grade malaria parasitaemia predisposes to lowered C3b inactivator levels that would enhance persistence of deposited immune complexes, and subsequent tissue damage where C3b receptors are present.