Maloys. Appl. Biol. (lune 2003) i2(I): 15-20 TIIE EFFECT OF Ml MONOCLONAL ANTIBODY ON IN VIVO FERIILIZATION IN HAMSTERS *MAHANEM, M.N. and DZULSUHAIMI, D. School of Biosciences & Biotechnology, Faculty of Science & Technology Universiti Kebangsaan Malaysia, 43600 Bangi Selnngor, Malaysia ABSTRACT The Ml monoclonal antibody (mAb) recognizes an antigenic protein, localized at the equatorial segment of the hamster sperm head. A previous study had shown that Ml mAb blocked sperm-oocyte fusion in hamster. In this experiment, passive immunization of female hamsters were conducted to study the effect of Ml mAb on in vivo fertilization. Superovulated female hamsters received two doses of antibody injections, intraperitoneally (at time similar to the PMSG & hCG injections schedule) at concentrations of 0.5, 1.0, 2.0, 4.0 and 8.0 mg Ml mAb respectively. Two weeks after mating with proven fertile male hamster, the females were killed and implantation sites were counted. M1 mAb at 2.0, 4.0 and 8.0 mg showed a significant decrease in number of implantation sites (P < 0.05) compared to 0.5, 1.0 mg M1 mAb and the control group. Histological studies on ovaries and uterus showed no evidence of pathological changes in control and treated females. These results suggest a possible basis for the development of Ml antigen as a contraceptive vaccine, employing specific sperm antigens that participate in the fertilization process. ABSTRAK Antibodi monoklon Ml yang mengenali protein antigenik Ml berada di segmen khatulistiwa kepala sperma hamster. Kajian terdahulu menunjukkan antibodi monoklon M1 telah menghalang pelakuran sperma-oosit hamster. Dalam kajian ini imunisasi pasif ke atas hamster betina telah dilakukan untuk mengkaji kesan antibodi monokoln terhadap persenyawaan in vivo. Hamster betina yang dirangsang ovulasi disuntik dengan dua dos suntikan antibodi secara intraperitoneal (pada masa yang sama dengan suntikan PMSG dan hCG) pada kepekatan 0.5, I .0, 2.0, 4.0 dan 8.0 mg antibodi monoklon Ml masing-masing. Dua minggu selepas kopulasi dengan hamster jantan yang terbukti subur, haiwan betina dimatikan dan bilangan tapak implantasi ditentukan. Suntikan antibodi monoklon Ml pada 2.0, 4.0 dan 8.0 mg didapati menunjukkan penurunan bilangan tapak implantasi dengan signifikan (P < 0.05) berbanding suntikan antibodi monoklon pada 0.5, 1.0 mg dan kawalan. Kajian histologi ovari dan uterus pula menunjukkan tiada bukti berlaku perubahan patologi dalam kumpulan haiwan betina perlak-uan dan kawalan. Keputusan kajian mencadangkan potensi pembangunan antigen Ml sebagai vaksin kontraseptif, menggunakan antigen spesifik sperna yang mengambil bahagian dalam proses persenyawaan. Key words: Ml monoclonal antibody, passive immunization, in vivo fertilization. INTRODUCTION The relationship between the effect of immunization with sperm and reduced fertility is well established (Tung et al., 1979). Molecules unique to the sperm cell, which are necessary for the occurrence of fertilization may elicit antibody production (Saling and Waibel, 1985). It is generally believed that the presence of anti-sperm antibodies in blood sera and/ or reproductive tract fluid cause sperm agglutination, immobilization of spern, interference of sperm-egg interactions and inhibition of development or implantation of early embryos (Menge, 1980). Through hybridoma technology, it has become possible to generate epitope-specific monoclonal antibodies (mAbs) to numerous sperm antigens (Bellve and Moss, 1983). Monoclonal antibodies are ideal tools to understand the mechanisms of fertility regulation by monitoring their effects on sperm-egg interactions or development of early embryos (Lee et a1., 1985). To date several studies have been performed to understand the roles of functional molecules such as sperm fusion antigen(s) located specifically at the sperm equatorial segment region. Rat epididymal protein (DE protein) (Cohen et al., 2000), the 34 * To whom correspondence should be addressed.