Active immunization against riboflavin carrier protein results in peri-implantation embryonic loss leading to pregnancy termination in rats: use of alternate adjuvants.

ABSTRACT

To investigate the mechanism of pregnancy termination following immuno-neutralization of riboflavin carrier protein (RCP) and to use acceptable adjuvants, we actively immunized female rats with reduced and carboxymethylated RCP (RCM-RCP) using various adjuvants (during primary immunization) such as sodium phthalylated lipopolysaccharide (SPLPS), purified S. typhi outer membrane proteins (porins) and a combination of them. Rats (5-14 per group) were immunized with alugel adsorbed RCM-RCP (100 microg/dose) either alone or with SPLPS or porins or SPLPS+porins. Control animals received RCM-RCP emulsified with Fruend's completelincomplete adjuvants (FCA/FIA). All animals received five boosters at intervals of 21 days. The lowest (4 X 10(-3)) and the highest (> 70 X 10(-3)) anti-RCM-RCP antibody titers were observed in alugel adsorbed-RCM-RCP group and control groups, respectively. Immunized animals showed reduced fertility following 3rd, 4th and 5th boosters. Reduction in fertility was 30-60% in alugel adsorbed RCM-RCP group, 90-100% in FCA-RCM-RCP group and 80-90% in SPLPS+porins group. Fertility reduction was not strictly correlatable with the serum antibody titers. RCP-specific IgG could be localized in the uterine endometrial glands and luminal epithelial cells in the immunized animals. Animals in the FCA/FIA group showed abnormal implantation/resorption sites and their histological sections showed degenerated embryos. But, day 5 preimplantation embryos were normal. These results show that (a) SPLPS+porins can be used as adjuvants in place of FCA/FIA for active immunization against RCM-RCP and (b) early termination of pregnancy in the immunized animals is due largely to the failure of normal embryo implantation.