The role of bacterial contamination in the isolation of apparent anti-inflammatory factors from rabbit anti-lymphocytic serum.

1 Rabbit anti-guinea-pig lymphocytic serum was fractionated by gel filtration to obtain partially purified materials possessing anti-inflammatory activity. The pharmacological properties of these materials were then studied. 2 Two fractions were found which reproducibly contained significant activity. One of these activities caused inflammation at the site of injection and was associated with high molecular weight protein (2008000). The other activity was found in low molecular weight fraction but was shown to be due to small amounts of endotoxin from Gram negative bacteria. These organisms contaminated the fractions in spite of the recommended precautions for gel filtration having been taken. 3 The endotoxin-containing fraction completely abolished leucocyte infiltration into the rat foot which had been injected with kaolin. It had no apparent effect on circulating haemolytic complement. It caused maximal elevation of serum 11-hydroxycorticosteroid concentrations and was found to cause the release of pharmacologically active amines. Many of the previously reported naturally occurring anti-inflammatory substances have similar pharmacological properties to those of the endotoxin-containing fraction. 4 It was concluded that doubt will exist about the presence of anti-inflammatory factors in mammalian body fluids unless stringent precautions are taken to exclude measurable bacterial contamination. 5 These experiments also cast doubt on the validity of accepted procedures for excluding microbial growth from columns used in the fractionation of serum.