The probable role of Babesia argentina esterase in the in vitro activation of plasma prekallikrein

The purification of an esterase from B. argentina parasites, using affinity chromatography is described. Two fractions were obtained from crude “L” and “S” parasite extracts. The second fraction from each extract obtained after desorption of the column had a greatly enhanced esterase specific activity. When added to normal plasma and incubated at 37°C for 60 min, the second L₁ fraction activated between 12.1% and 72.3% of bovine plasma prekallikrein and the second S₁ fraction, 76.3% and 87.1%. Only slight activation occurred with fraction 1 of L₁ and S₁, and none with normal red cell components. The active fractions were associated with a fibrinogen-like substance and caused fibrin formation in vitro. The implications of these findings are discussed.