The opsonic activity of complement to rough strains ofEscherichia coli in vivo in newborn precolostral pigs

The participation of complement of newborn precolostral piglets (in the absence of antibody) in the opsonization of roughEscherichia coli was investigated using blood clearance test. It was found that the complement inhibitor-yeast mannan inhibits thein vivo blood clearance when injected i. venously into newborn precolostral piglets. This inhibition takes place at the serum level and not by saturation of RES cells by mannan: sera from mannan-treated piglets are not bactericidal in anin vitro bactericidal assay against roughEscherichia coli; secondly, the presence of antibody removes the blockade of phagocytosis by mannan indicating that the RES cells are functionally capable to perform phagocytosis. On the basis of our findings we postulate that in newborn precolostral piglets in which antibody is not present in their sera, complement alone (or with cooperation with other unknown serum component) acts as an opsonin on roughEscherichia coli and is responsible for the blood clearance rate of these bacteria.