Further Studies on M‐components With Antistreptolysin O Activity. The Inactivating Effect on Different Oxygen‐labile Haemolysins

Ten individual human serum samples with high concentrations of monoclonal γG globulins neutralizing streptolysin O were examined with three oxygen‐labile bacterial haemo‐lysins, which are antigenically related to streptolysin O. The haemolysins studied were pneumolysin of Diplococcus pneumoniae , tetanolysin of Clostridium tetani , and ø toxin of Glostridium perfringens (= Cl. welchii ). They were not inhibited to any appreciable extent by the human sera except in one of the thirty possible combinations. This exception was remarkable because the serum sample neutralized pneumolysin and streptolysin O equally well. The results are discussed in relation to the marked cross‐reactivity of immune sera from horses.