Summary.A 29-Kda cytotoxic molecule of axenically-grown pathogenic Entamoeba histolytica (strain HM 1) was purified from an amoebic extract by immuno-affinity chromatography with monoclonal antibodies. Immunoreactivity of the purified 29-Kda molecule altered significantly (p < 0.01) after exposure to heat or trypsin, but remained unaltered after treatment with sodium metaperiodate. The 29-Kda molecule was recognised by serum from each of 13 patients with amoebic liver abscess. In an ELISA system, the molecule produced significantly higher (p < 0.01) OD readings with these serum samples than with samples from asymptomatic cyst passers. No serum from healthy subjects or from patients with idiopathic ulcerative colitis or giardiasis had antibodies that reacted with the 29-Kda molecule. The immune response to the 29-Kda amoebic protein in man may indicate a specific role for this molecule in invasive amoebiasis.

Summary.A micro-enzyme linked immuaosorbent assay (micro-ELISA) has been evaluated as a diagnostic test to detect amoebic antigen in polyethylene glycol (PEG) precipitated circulating immune complexes (CIC) in sera from patients with amoebiasis. The immune complexes were captured on rabbit anti-amoebic IgGcoated wells of microtitration plates and the complexed antigen was detected by enzyme linked antihuman immunoglobulins. A titre of > 160 for the immune complexes was considered to be of clinical significance. The immunoassay detected amoebic, antigen-specific CIC in 35 (94.5%) of 37 patients with confirmed amoebic liver abscess. Twenty (55.5%) of 36 clinically suspected cases of amoebic liver abscess had amoebic antigen-specific CIC and responded favourably to anti-amoebic chemotherapy. Only two (20%) of 10 cases of non-dysenteric symptomatic intestinal amoebic infection had amoebic antigen-specific CIC. One (10%) of 10 patients with non-amoebic intestinal disorders also had amoebic antigen in CIC. However, none of 15 cases of non-amoebic hepatic disorders that included hydatid disease, metastatic adenocarcinoma, hepatocellular carcinoma, cholecystitis and choledocal cyst, 13 cases of rheumatoid arthritis and 25 apparently healthy subjects had amoebic antigen in CIC. The levels of the amoebic antigen-specific CIC did not correlate (p>O-O5) with either the number of abscess(es) or lobe(s) of the liver involved. However, the levels of antigen-specific CIC were higher (p < 0.01) in patients with a liver size of more than 5 cm below the right costal margin. Antigen-specific CIC levels tended to decline or disappear during 3-6 months following completion of therapy. In spite of the limitations for diagnosing symptomatic intestinal amoebic disease, the demonstration of specific CIC is recommended as an immuno-diagnostic procedure for patients with suspected amoebic liver abscess.

Monoclonal antibodies have been developed and used as specific probe to locate and identify a 29‐kDa molecule of axenic Entamoeba histolytica trophozoites. Monoclonal antibody produced by clone C8 (MoAb C8) strongly agglutinated the amoebic trophozoites. THe immunofluorescence of live E. histolytica trophozoites and surface fluorescence of acetone‐fixed trophozoites by MoAb C8 indicated existence of a 29‐kDa molecule on surface‐associated plasma membrane of E. histolytica. The monoclonal antibody belonged to IgG1 isotype. The prior treatment of E. histolytica trophozoites with MoAb C8 resulted in significant (P < 0.01) reduction in adherence of amoebic trophozoites to cultured Chinese Hamster Ovary cells and significant (P < 0.01) reduction in cytotoxicity to cultured Baby Hamster Kidney cells. Pretreatment of amoebic trophozoites with MoAb C8 prior to cultivation in TPS‐1 medium resulted in significant (P < 0.01) reduction in growth of the parasite. Thus, the data suggested that the surface‐exposed 29‐kDa molecule may be one of the receptors involved in E. histolytica host cell interactions and may possibly modulate amoebic disease processes.

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