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 (S PLPS), purified <i>S</i>. <i>typhi </i>outer membrane proteins (porins) and a combination of them. Rats (5-14 per group) were immunized with alugel adsorbed RCM-RCP (100 μg/dose) either alone or with SPLPS or porins or SPLPS+porins. Control animals received RCM-RCP emulsified with Fruend's complete/incomplete adjuvants (FCA/FIA). All animals received five boosters at intervals of 21 days. The lowest (4 × 10^-3) and the highest (> 70 × 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

<span style="font-size:12.0pt;line-height:115%;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-ansi-language:en-in;mso-fareast-language:="" en-in;mso-bidi-language:hi"="">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.</span>