Comparison of Complement Activity in Adult and Preterm Sheep Serum

Abstract

Guinea pig erythrocytes were identified as the optimal target, although sensitizing them with rabbit antiguinea pig erythrocyte antibody did not enhance the lysis by maternal sheep serum. In contrast, preterm neonatal sheep serum was unable to efficiently lyse guinea pig erythrocytes unless pre-sensitized with antibody. Further investigation revealed that maternal serum contained high levels of antibodies that cross-reacted with guinea pig and rabbit erythrocytes, while no cross-reacting antierythrocyte antibodies were found in preterm neonatal serum. Therefore, unlike primates, rabbits, and guinea pigs, no transplacental transfer of maternal IgG to foetal sheep occurs. Use of exogenous complement regulators is often used to dissect the contribution of complement to disease pathogenesis; however, we found that while full-length soluble human complement receptor 1 (sCR1, CDX-1135) was able to inhibit lysis of guinea pig erythrocytes by human and rat serum, no inhibition of sheep serum could be observed. Investigation of complement contribution to disease pathogenesis in the future will require the identification of an inhibitor that is effective against sheep complement.

Proof of principle: Physiological transfer of small numbers of bacteria from mother to fetus in late-gestation pregnant sheep

“…Elegant experiments in the mouse model clearly demonstrate that bacteria introduced into the maternal mouth inform the development of the innate immune system of the offspring [15]. Maternal-fetal transfer in those experiments was largely dependent on maternal IgG, which is known to be transferred across the placenta in both mouse [16] and human [17], although IgG transfer is not thought to occur in sheep [18]. Interestingly, though, recent transcriptomics modeling of ontogenetic patterns of gene expression in the fetal brain demonstrate that the major pattern of increasing gene expression in the fetal brain is the development of hematopoietic immune cells [19].…”

Preterm Birth, Intrauterine Infection, and Fetal Inflammation

“…Analysis of data from modified CH 50 assays using serum from fetuses delivered at 125-day (term is between 145 and 150 days) revealed a pattern of lytic activity similar to that of maternal sheep serum. In contrast, maximum lysis using serum from earlier gestational ages (85 and 95 days) was approximately twofold lower ( 46 ).…”

Foetal Ureaplasma parvum bacteraemia as a function of gestation‐dependent complement insufficiency: Evidence from a sheep model of pregnancy

“…Haemolysis assays were performed as previously published. 15 Guinea pig erythrocytes were 132 purchased from TCS Biosciences (Oxford, UK) and sensitised with rabbit polyclonal anti-133 guinea pig erythrocyte antibodies purchased from Fitzgerald Industries International (North 134 Acton, MA), as described previously. 15 to 4 h (data not shown).…”

“…15 Guinea pig erythrocytes were 132 purchased from TCS Biosciences (Oxford, UK) and sensitised with rabbit polyclonal anti-133 guinea pig erythrocyte antibodies purchased from Fitzgerald Industries International (North 134 Acton, MA), as described previously. 15 to 4 h (data not shown). Bactericidal activity was found to be calcium dependent for both 193 preterm and adult sera, as dilution in 10mM EGTA with additional Mg 2+ showed no killing 194 when complement activity was restricted to the alternative activation pathway ( Figure 1B).…”

“…with guinea pig erythrocytes15 and this was not detected in any of the sera from the 326 preterm lambs (data not shown). 327328The HPA5 strain is susceptible to human serum killing in the absence of specific anti-UP 329 antibodies.…”