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.

Improved detection of immune complexes in human and mouse serum using a microassay adaptation of the C1Q binding test

A microassay adaptation of the [125I]C1q binding test for the detection of circulating immune complexes is described. This technique is more rapid to perform, requires smaller volumes of serum and reagents, and surprisingly, increases the sensitivity of the assay when compared to the previously reported C1q binding method.

Circulating and tissue-bound immune complex formation in murine malaria

Immune complex formation during Plasmodium berghei infection of OF1 mice was investigated. Circulating immune complexes (CIC) were detected by the Clg-binding assay and the conglutinin-binding solid-phase assay in lethal or drug-limited infections. CIC appeared on day 9 of infection, peaked on day 11, and disappeared only after complete cure of the infection. Analysis of the immune complexes detected by the Clq-binding assay revealed the following characteristics: sedimentation coefficients of 13S to 21S, resistance to DNAse, and selective removal by filtration through protein A bound to Sepharose. Glomerular deposits of IgM preceded the appearance of CIC, whereas deposits of IgG and C3 were concomitant with the appearance of CIC. Tissue-bound immunoglobulins were also found in the choroid plexus. The appearance of anti-malarial antibodies and malarial antigens in the serum was closely associated with a depression of C3 levels and the presence of CIC. Drug treatment was followed by normalization of C3 levels, and clearance of both CIC and malarial antigens.