The 170-kDa subunit of the galactose-inhibitable adherence lectin of Entamoeba histolytica mediates attachment to colonic mucins and host cells. The DNA fragment encoding the 170-kDa subunit was produced by polymerase chain reaction (PCR) and divided into four sections by restriction endonucleases. The third section (designated LC3, base pairs 2273-3397) encodes a cysteine-rich fusion protein that was recognized by adherence-inhibitory anti-lectin monoclonal antibodies and serum antibodies from 95% of subjects with amebic liver abscess. Immunization of gerbils with purified recombinant LC3-encoded protein (10 micrograms) with Titermax adjuvant elicited a high-titer serum anti-LC3 IgG antibody response and protective immunity against intrahepatic challenge with 0.5 x 10(6) virulent axenic trophozoites (strain HM1:IMSS; 71% vaccine efficacy, P < .01). In summary, a recombinant cysteine-rich portion of the 170-kDa lectin subunit was highly antigenic, immunogenic, and effective as a subunit vaccine in an experimental animal model of amebic liver abscess.

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We followed 93 subjects with amebic liver abscess (ALA) and 963 close associate controls at 3-month intervals for 36 months to characterize intestinal and humoral antibody responses to the amebic galactoseinhibitable lectin and to determine whether immunity developed to Entamoeba histolytica or Entamoeba dispar infection following cure of ALA. We found that ALA subjects had a higher prevalence and level of intestinal antilectin immunoglobulin A (IgA) and serum anti-LC3 (cysteine-rich recombinant lectin protein) IgA and IgG antibodies, P < 0.01 and P < 0.05, respectively, compared to controls. The intestinal antilectin IgA antibody response was sustained over a longer time period in ALA subjects (71.8% remained positive at 18 months and 52.6% at 36 months, P < 0.001 compared to 17.6% and 10.3% of controls, respectively). ALA subjects were highly immune to E. dispar infection throughout the study (0% infected at 6 and 36 months, compared to 6.5% and 4.9% of control subjects, respectively, P < 0.05). Upon entry into the study, 6.3% of ALA subjects were infected with E. histolytica; the incidence of new E. histolytica infections in controls (as determined by culture) was too low (1.4%) to determine whether ALA subjects exhibited immunity to new infections. We found that stool cultures every 3 months markedly underestimated the occurrence of new E. histolytica infections, as 15.3% of controls seroconverted after 12 months of follow-up. Unfortunately, under the field conditions present in Durban, South Africa, enzyme-linked immunosorbent assay for detection of lectin antigen in stool yielded unreliable results. In summary, subjects cured of ALA exhibited sustained mucosal IgA antibody responses to the amebic galactose-inhibitable lectin and a high level of immunity to E. dispar infection. Determination of immunity to E. histolytica following cure of ALA will require the use of more sensitive and reliable diagnostic methods.One of the major questions in amebiasis research is whether cure of invasive disease is followed by development of immunity to new intestinal infections and, thus, recurrence of disease. The enteric protozoan Entamoeba histolytica is one of the leading parasitic causes of death worldwide. Disease results from the parasite's ability to invade the colon, causing amebic colitis, or spreading via the portal venous system to the liver, resulting in formation of an amebic liver abscess (ALA). Amebic liver abscesses are more common in adult men and were thought to be fatal if untreated (7). A recent study in Hue, Vietnam, revealed that ALA is even more common than previously realized and may occur frequently in a subclinical manner (10). One large noncontrolled study reported that the rate of recurrence of amebic liver abscesses over 5 years in a highrisk population was less than expected compared to historical controls (14). In a cross-sectional study, the point prevalence of Entamoeba species intestinal infection was lower in subjects who possessed serum antiamebic antibodies (13).The E. histolytica gala...

Abstract. An ELISA for detection of serum IgM antibodies to the galactose-inhibitable adherence lectin of Entamoeba histolytica revealed that 2.8% of uninfected controls, 0.0% of controls infected with other parasites, 13.4% of asymptomatic amebic infections, 55% of colitis patients, and 77% of amebic liver abscess patients from Cairo, Egypt and Durban, South Africa had serum anti-lectin IgM antibodies. Of acute amebic colitis patients with symptoms for less than one week, only 6% possessed serum IgG anti-lectin antibodies, yet 45% had serum IgM antibodies to the amebic lectin. This compares with 65% of sera in acute colitis patients positive for lectin antigen as determined by ELISA with anti-lectin monoclonal antibodies. In conclusion, an ELISA for serum anti-lectin IgM antibodies appears to have greater clinical utility in the setting of acute amebic colitis than an ELISA for anti-lectin IgG antibodies, but is no more sensitive than an ELISA for detection of lectin antigen in sera.In some protozoal infections, the measurement of IgM antibodies is helpful in identification of current and postinfection states, such as giardiasis 1 and toxoplasmosis. 2 Detection of anti-Entamoeba histolytica IgM antibodies may constitute an important strategy for early diagnosis. Regression of the serum anti-amebic IgM antibody response occurs within three months in 50% of cases and reappearance or a later increase in anti-amebic IgM antibody titer represents an important prognostic factor. 3 The relatively short duration of the anti-amebic IgM antibody response has also been confirmed by Jackson and others 4 compared with the persistence of anti-amebic IgG serum antibodies for years after cure of invasive amebiasis. 5 Serum IgM antibodies to amebic plasma membrane antigens were detected previously with high specificity and sensitivity by an ELISA procedure. 6 Reactivity of anti-amebic IgM antibodies to small (5-15 kD) cytoplasmic membrane antigens has been demonstrated. 6 The use of well-characterized native amebic surface antigens may improve the diagnostic utility of serologic tests. The galactose-inhibitable lectin of E. histolytica mediates adherence of trophozoites to colonic mucins, epithelial cells, and host inflammatory cells. 7-9 Galactose-inhibitable lectin binding is absolutely required for amebic lysis of mammalian cells. 8 We used an ELISA with purified native amebic lectin, 10,11 which contains a highly conserved 170-kD antigen subunit that is recognized by serum IgG antibodies from patients worldwide with invasive amebiasis. 10,12-14 Lectin antigenemia has been demonstrated in patients with invasive amebiasis. 15,16 Amebic lectin has been detected in feces from patients with E. histolytica or E. dispar intestinal infections. 15,17 Previous studies have demonstrated that subjects with other parasitic infections do not generate antibodies to the amebic lectin and that anti-lectin monoclonal antibodies are specific for E. histolytica and E. dispar lectin epitopes. 11,13,15,16 In our study, we determined whether dete...

SummaryWe studied 84 consecutive patients presenting with acute diarrhoea (less than 1 week in duration) at an outpatient tropical medicine clinic in Cairo, Egypt. The diagnosis of amoebic colitis was established by the presence of Entamoeba histolytica galactose-inhibitable lectin antigen and the presence of occult blood in stool. Controls were 182 healthy regional people and 64 patients complaining of prolonged diarrhoea lasting more than 1 week. Entamoeba histolytica infection was found more frequently in patients with acute diarrhoea (57.1%) than in healthy controls (21.4%) or patients with prolonged diarrhoea (25%) (P < 0.001). There was a higher prevalence of Entamoeba dispar infection in the two control groups (24.2 and 20.3%, respectively, P ¼ 0.004 and 0.061) compared with those with acute diarrhoea (8.3%). Of the 84 patients with acute diarrhoea 32 had amoebic colitis (38%), and of these, 31 (97%) had at least one positive assay for serum amoebic antibodies (P < 0.001 compared with control groups). In summary, as determined by antigen-detection enzyme-linked immunosorbent assay, there is an unexpectedly high prevalence of amoebic colitis among patients presenting with acute diarrhoea to a tropical disease clinic in Cairo, Egypt.