Immunopathological aspects of Plasmodium berghei infection in five strains of mice. I. Immune complexes and other serological features during the infection.

The development of circulating immune complexes was studied in mice of the BALB/c, A/J, OF1, CBA and C57B1 strains infected with P. berghei. Complexes were evaluated in relation to levels of parasitaemia, soluble antigen, specific antibody and C3. Susceptibility to infection was greatest in BALB/c, A/J and OF/a mice. The maximum parasitaemia was 30% in CBA and 70% in all other strains. Levels of soluble antigen paralleled those of parasitaemia. Specific antibody was detected in all strains, but the titre continued to rise throughout the infection only in CBA mice. Circulating immune complexes occurred in mice of all strains from day 6; the level fell after day 9 in C57B1 whereas it was maintained in CBA mice. The development of immune complexes was associated with marked depression of C3 levels in all except CBA mice, in which a transient reduction was followed by recovery. Partial characterization of the complexes showed that IgM-containing complexes appeared earliest and reached highest levels in BALB/c mice while in CBA mice, IgM complexes were found in lesser amounts and the level fell in late infection. IgG complexes rose throughout infection in CBA and fell in later stages in BALB/c and C57B1 mice. In nude BALB/c mice, immune complexes were usually not detectable and only low levels of antibody of IgM class were produced. Differences in mortality pattern could not be related to any single serological factor.