Strain-dependent variability in immune response to chicken riboflavin carrier protein in mice with different haplotypes

Active immunization of fertile female mice, rats and sub-human primates wit h linearized chicken riboflavin carrier protein (RCP) curtailed pregnancy s uggesting that sequence-specific RCP antibodies interfere with fertilizatio n/early embryo development. To investigate the genetic basis of variations in immunogenecity, antibody response to reduced and carboxymethylated RCP ( RCM-RCP) was studied in different strains of mice of independent H-2 haplot ypes. Among these, AKR (H-2(k)) were low or non-responders. Measurement of antibody titers in hyperimmune sera showed that among responder strains of mice, C57BL/6 (H-2(b)) and BALB/c (H-2(d)) generated higher levels of antib ody compared to mice of SJLJ (H-2(S)). The relative affinities of these ant ibodies also varied depending upon the strain, with BALB/c mice showing hig hest affinity. Epitope mapping by pepscan ELISA revealed significant variab ility in determinant-specific antibody populations, with SJLJ strain lackin g antibodies to N-terminal half of RCP sequence. However, four immunodomina nt sequential epitopes (residues 100-107, 134-141, 174-181 and 200-207) com mon to all the three strains of mice have been identified. Binding to these regions was not haplotype restricted although there were qualitative diffe rences in recognition patterns. Present investigations have shown that site -specific antibodies directed towards any one of the four epitopic regions comprising of residues 3-24, 64-83, 130-147 and 200-219 in chicken RCP sequ ence effectively interfered with pregnancy establishment in female BALB/c m ice. This implies the propensity of RCP antibodies to curtail pregnancy in the other two responder mouse strains also.