Preparation of recombinant human monoclonal antibody Fab fragments specific for Entamoeba histolytica

Genes coding for human antibody Fab fragments specific for Entamoeba histol ytica were cloned and expressed in Escherichia coli, Lymphocytes were separ ated from the peripheral blood of a patient with an amebic liver abscess. P oly(A)(+) RNA was isolated from the lymphocytes, and then genes coding for the light chain and Fd region of the heavy chain were amplified by a revers e transcriptase PCR. The amplified DNA fragments were ligated with a plasmi d vector and were introduced into Escherichia coli, Three thousand colonies were screened for the production of antibodies to E. histolytica HM-1:IMSS by an indirect fluorescence-antibody (IFA) test. Lysates from five Escheri chia coli clones were positive. Analysis of the DNA sequences of the five c lones showed that three of the five heavy chain sequences and four of the f ive light-chain sequences differed from each other. When the reactivities o f the Escherichia coli lysates to nine reference strains of E, histolytica were examined by the IFA test, three Fab fragments with different DNA seque nces were found to react with all nine strains and another Fab fragment was found to react with seven strains. None of the four human monoclonal antib ody Fab fragments reacted with Entamoeba dispar reference strains or with o ther enteric protozoan parasites. These results indicate that the bacterial expression system reported here is effective for the production of human m onoclonal antibodies specific for E, histolytica. The recombinant human mon oclonal antibody Fab fragments may be applicable for distinguishing E, hist olytica from E. dispar and for use in the serodiagnosis of amebiasis.