The membrane fractions were prepared from the samples of mouse peritoneal exudate cells in which polymorphonuclear leukocytes or macrophages were predominant. Each fraction was incubated at pH 5.6 with tubercle bacilli, staphylococci or E. coli in a high density. Time-course enumeration of viable bacteria in the mixture revealed that the decrease of viable count down to 1/100 was attained in more than ten hours for tubercle bacilli and within one hour for staphylococci. This bactericidal activity was enhanced by a membrane-active peptide (melittin) and inhibited by indomethacin, EDTA and heating of the membrane fraction. E. coli did not receive any killing effect under the same experimental conditions. The membrane fraction prepared from red blood cells was almost inactive against any species of above bacteria.
Melittin is an activator of phospholipase A2 but indomethacin and EDTA are the inhibitor. Therefore, phospholipase A2 activity of the membrane fraction was examined in the presence or absence of these agents and confirmed the expected results. All the above observations added a further support for our idea that hyperactivation of phospholipase A2 in the phagocyte membrane May act on endogenous phospholipids to release long-chain fatty acids in an enough amount to kill the sensitive bacteria. Discussion was made on the probable conditions which make the above in vitro event exists also in vivo.
