RECOGNITION OF GIARDIA-LAMBLIA CYST-SPECIFIC ANTIGENS BY MONOCLONAL-ANTIBODIES

Immunization of BALB/c mice with a sonicated extract of in vitro-gener ated Giardia lamblia cysts produced six cyst-specific monoclonal antib odies (MoAbs). Two MoAbs (8C5.C11 and 5A4.G6), which recognize protein aceous cyst antigens, were selected for further study. In indirect imm unofluorescence (IFA), MoAb 8C5.C11 reacted with encystation-specific vesicles in trophozoites beginning 3 h after the induction of encystat ion in vitro. This MoAb also recognized cysts which began to appear at 12 h. In contrast, MoAb 5A4.G6 stained only cyst walls. In Western bl ots, both MoAbs also reacted with cyst antigens, but not trophozoite a ntigens. MoAb 8C5.C11 first recognized cyst antigen from 3 h encysting cultures, reacting with 26, 28, 42 and 46 kD bands. MoAb 5A4.G6 react ed with a 38 kD band beginning with 12 h encysting cultures. When adde d to G. lamblia encysting cultures before the appearance of cysts (0 t o 9 h) and in the presence of a source of complement, MoAb 8C5.C11 cau sed a significant reduction in the numbers of water-resistant cysts pr oduced in vitro compared to the control. MoAb 5A4.G6 did not affect in vitro encystation. These findings confirm the heterogeneity of cyst a ntigens, and also indicate that the pr ocess of encystation in vitro c an be interrupted by antibodies and complement.