Exoerythrocytic development of Plasmodium gallinaceum sporozoites in a chicken fibroblast cell line and inhibition of the cell invasion by specific anti-sporozoite monoclonal antibodies.

Cultivation of the Plasmodium gallinaceum exoerythrocytic forms from sporozoites was attempted in three different cell lines: HEPG2-A16 (from a human hepatoma), VERO (monkey kidney epithelial cells) and SL-29 (chicken embryo fibroblast cells). The sporozoites invaded all three cells types but their development into exoerythrocytic forms occurred only in the SL-29 cells. In the presence of specific monoclonal antibodies against the major circumsporozoite protein, there were varying degrees of inhibition of parasite invasion of the SL-29 cells. Of seven monoclonal antibodies tested, two completely inhibited cell invasion at high concentrations and caused intense inhibition at concentrations as low as 2.5 micrograms/ml, four caused intense inhibition at these various concentrations, and one had no effect on sporozoite invasion.

Common epitopes in the circumsporozoite proteins of Plasmodium berghei and Plasmodium gallinaceum identified by monoclonal antibodies to the P. gallinaceum circumsporozoite protein.

Monoclonal antibodies that react with the circumsporozoite protein of the avian malaria Plasmodium gallinaceum sporozoites also reacted with circumsporozoite protein of the rodent malaria Plasmodium berghei. Two types of reactivity were identified: 1) two monoclonal antibodies reacted with P. berghei sporozoite protein by enzyme-linked immunosorbent assay, Western blot and indirect immunofluorescence antibody, 2) six other monoclonal antibodies reacted with P. berghei sporozoites by ELISA and Western blot only. We studied whether these differences could be explained by reactivity in enzyme-linked immunosorbent assay with different P. berghei circumsporozoite peptides. Although all P. gallinaceum monoclonal antibodies reacted with the P. berghei repeats, the first group reacted with a conserved peptide sequence, N1, whereas the second group did not. These results suggest that circumsporozoite proteins from P. gallinaceum and P. berghei share common epitopes. The biological significance of our finding is not yet clear. Indeed, the cross-reactive monoclonal antibodies giving a positive indirect immunofluorescence antibody with the P. berghei sporozoites only caused a borderline effect on the living P. berghei parasites in vitro as measured by inhibition of sporozoite infectivity.