Lysis and immobilization of Giardia muris trophozoites in vitro by immune serum from susceptible and resistant mice.

To define the potential role of antibody in host defence against Giardia muris, comparative assessment of in-vitro anti-trophozoite effects of immune serum obtained from susceptible (A/J) and resistant (B10.A) mice was done. Two anti-parasite effects of serum were identified and quantified: lysis and immobilization of trophozoites. These giardicidal activities were present in the serum from both A/J and B10.A mice. Maximal lysis of trophozoites by serum from A/J or B10.A mice was 40 to 50%. The lysis of trophozoites was abolished after incubation of serum at 56 degrees C for 30 min. The addition of exogenous complement restored lytic activity of heat-inactivated serum. The immobilization of trophozoites was dependent on both the duration of incubation and concentration of serum. After 30 min of incubation, over 98% of trophozoites were immobilized by immune serum from A/J or B10.A mice. There was no apparent relationship between the capacity of immune sera from A/J and B10.A mice to kill trophozoites in vitro and the ability of these strains of mice to control the infection with G. muris.