Wuchereria bancrofti: identification of parasitic acetylcholinesterase in microfilariae infected human serum

Abstract

An antigen with cholinesterase activity was detected in the sera of patients infected with Wuchereria bancrofti. The asymptomatic microfilaremic sera showed 3 to 4 times more cholinesterase activity for acetylthiocholine (ATCh) as compared to sera of symptomatic amicrofilaremic, hookworm infected and endemic normals, whereas the activities for butyrylthiocholine (BTCh) did not significantly differ. The enzyme activities from both sources, namely from sera of microfilaremic cases and from endemic normals, were partially purified and according to substrate specificity for ATCh and BTCh as well as inhibition of the former activity by excess substrate classified as acetylcholinesterase (AChE; EC 3.1.1.7) and pseudocholinesterase (AChE; EC 3.1.1.8), respectively. The Km-value for ATCh of the cholinesterase from the microfilaremic sera was determined to be 0.87 mM. Eserine competitively inhibited the AChE activity; the inhibition constant was found to be 1.3 microM. The BChE from the normal sera had Km-values of 0.15 and 0.20 mM for BTCh and ATCh, respectively, and did not show significant inhibition by eserine. These and other dissimilarities suggest a difference in nature of the cholinesterases in microfilaremic and normal sera and propose that the former enzyme, a true acetylcholinesterase, originates from the parasite. Additional evidence for the origin of the AChE-activity from the parasite was provided by ELISA-studies; anti-Brugia malayi AChE antibodies confirmed antigenecity and cross reactivity of the AChE in infected sera, whereas the antibodies did not show any cross reactivity with the BChE in normal sera.