Immunization with a synthetic peptide conjugate derived from the N-terminal sequence of either the beta-chain of haemoglobin or the immunosuppressiveprotein (reOLT 4) reduces the litter size of pregnant rats

A synthetic peptide conjugate based on the N-terminal sequence of a 10 000 MW immunosuppressive serum protein (reOLT 4) was used to immunize female Le wis rats prior to mating, in order to determine whether blocking this prote in had an effect on pregnancy. The N-terminal sequence of (reOLT 4) has clo se sequence homology to the beta-chain of rat haemoglobin so a peptide conj ugate based on the N-terminal sequence of this protein was also used to imm unize female Lewis rats. Controls included animals that were not immunized and animals that received the peptide carrier, diphtheria toroid (DT). No s tatistical differences were found in gestation time or litter sizes in thes e groups. Differences were, however, evident between these groups and anima ls that received DT-(reOLT 4) (group 3) or the DT-beta-chain haemoglobin (g roup 5), There were no statistical differences in litter size or gestation time for group 4 when compared with group 5. Enzyme-linked immunosorbent as say and dot-blot analysis revealed that rats from both group 4 also had str ong responses against DT. the peptide conjugate they were immunized with an d the corresponding full-length protein. In both cases, animals from group 3 and group 5 had weak responses to the peptide that they did not receive, together with lower erythrocyte counts and haematocrits, and elevated heart to body weight ratios. Additionally, antibody purified on a (reOLT 4) immu noaffinity column was capable of binding to rat erythrocytes, A second inve stigation comparing anaemia prior to fertilization and maintained anaemia o ver the gestation period revealed that only the latter was; capable of decr easing litter size to the same degree as obtained for groups 3 and 5. We co nclude that for groups 4 and 5 it is the autoimmune effect of continual ana emia over the gestation period, mediated by autoantibodies. which results i n the observed lower litter size.