Activated vitronectin is adsorbed preferentially from serum by capsulate and acapsulate Opc-expressing N. meningitidis.

(A) To assess which serum protein is preferentially removed from serum by Opc⁺ Nm, a sample of normal human serum was adsorbed three times sequentially with Opc-expressing phenotype of acapsulate C751. At each stage, aliquots of the adsorbed serum samples were retained. Unadsorbed serum and adsorbed samples were analysed by immuno-dot blot assay (followed by densitometric analysis) for activated and total Vn/Fn levels using the mAb 8E6 and the polyclonal rabbit anti-Vn or anti-fibronectin antibodies. The levels of each of these components extracted from serum by Opc⁺ Nm as a percent of the total present at the start of extraction are shown. In control experiments, in which Opc⁻ Nm were used, 8E6 binding to 3 x adsorbed serum did not alter significantly and amounted to less than 10% loss of aVn (blank column). (B) In a similar experiment, a sample of NHS was adsorbed sequentially with capsulate MC58 Opc⁺ and Opc⁻ phenotypes. The Opc⁺ bacteria effectively removed a large portion of aVn as assessed by mAb 8E6 binding to serum samples before and after incubation with Nm (B, left). Specific removal of Vn from NHS by Opc⁺ but not Opc⁻ MC58 isolates is apparent from the analysis of serum-adsorbed bacterial pellets which show that bound Vn was only significantly detectable on Opc⁺ bacteria that were exposed to NHS (B, right).