Inhibition of complement-mediated lysis of sheep erythrocytes by cell-free preparations from Streptococcus mutans BHT.

A cell-free extract from the spent medium of Streptococcus mutans BHT was tested for anti-complementary activity with sheep erythrocytes (E) as target cells. It was determined that this extract was enriched for extracellular lipoteichoic acid (LTA) and that the LTA bound to the surfaces of sheep E. Furthermore, sheep E, sheep E plus antibodies (EA), and sheep cells in the intermediate stage of complement (C) component fixation EAC14 became refractory to C-mediated lysis after treatment with the LTA-rich extract. Sheep E in the intermediate states EAC142 and EAC1423567 were unaffected despite the fact that LTA could be detected on the surfaces of these cells with the passive hemagglutination procedure. Preliminary results showed that the C inhibitory activity co-purified with LTA, and LTA (both crude and purified) from other bacteria were anticomplementary. Both crude extracellular material from S. mutans BHT and partially purified extracellular LTA from the same bacteria caused consumption of whole human C activity.