Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 31. (Budapest, 1998)

The antiparasitic effect of antibodies was also evaluated in vitro using a short-term culture of P. berghei. In vitro invasion of normal erythrocytes by P. berghei was inhibited in the presence of immune sera (Fig. 4). Prechallenge serum from mice immunized with the SIII fraction inhibited about 89% of the invasion, whereas, total parasite homogenate (HOM) inhibited 75% invasion. Agglutination of some trophozoites and schizonts was observed in culture smears and a few merozoites were also found attached to erythrocytes. The prechallenge sera of mice immunized with SI did not show any significant inhibition of invasion. Concentration of interleukin (IL-1) in prechallenge immune sera of the SIII-FCA fraction was considerably high (305.0 pg/ml) as compared to controls (pg/ml). However, concentration of IL-1 in postchallenge immune serum came down to normal ( pg/ml). The differential centrifugation of total parasite homogenate resulted in various sediments. These sediments were analysed for the activity of different marker enzymes (Table 1). SIII (24,000 g pellet) contained maximum activity of acid phosphatase and acid protease while alkaline phosphatase activity was maximum in SI. The data given are of three independent preparations and the maximal activity of the marker enzymes was observed in their respective fractions. Table 1 Specific activity of marker enzymes in total parasite homogenate of P. berghei and its different sediments (results are the mean of three experiments, each run in duplicate along with appropriate controls) Enzyme (units/mg protein) Fraction Acid protease Acid phosphatase Alkaline phosphatase Horn 1.296±0.009 11.101±0.050 2.360±0.003 SI 0.938±0.003 2.172±0.009 18.170±0.910 SII 0.894±0.010 0.992+.0.002 1.730+0.001 SIII 5.573±0.091 13.840±0.090 4.379±0.003 SIV 1.100+0.040 1.40910.003 2.05U0.090 DISCUSSION SIII, the sediment obtained after centrifugation at 24,000 g of P. berghei, induced immune response in mice against the parasite, and all the immunized animals were protected upon challenge. The immune response appears to be both humoral and cellular. Humoral immunity is evident from the observations of high antibody titre determined by IFA (Fig. 3) and significant blocking of host cell invasion by merozoites in vitro resulting in a lower number of new rings formed and reduced propagation of parasite in the presence of immune serum (Fig. 4). As compared to the normal mice the high concentration of IL-1 in the sera of immunized animals and subsequent protection of these animals upon challenge shows that SIII elicited also a cellular response.