Neutralizing monoclonal antibody epitopes of the Entamoeba histolytica galactose adhesin map to the cysteine-rich extracellular domain of the 170-kilodalton subunit.

Entamoeba histolytica adheres to human colonic mucins and colonic epithelial cells via a galactose-binding adhesin. The adhesin is a heterodimeric glycoprotein composed of 170- and 35-kDa subunits. Fragments of the hgl1 gene encoding the 170-kDa subunit were expressed as recombinant fusion proteins in Escherichia coli and reacted with anti-adhesin monoclonal antibodies (MAbs) or pooled human immune sera. The MAbs tested recognize seven distinct epitopes on the 170-kDa subunit and have distinct effects on the adherence and complement-inhibitory activities of the adhesin. All seven MAbs reacted with a fusion protein containing the cysteine-rich domain of the protein. Pooled human immune sera reacted with the same cysteine-rich domain as the MAbs and also with a construct containing the first 596 amino acids. Reactivity of three MAbs with the surface of intact trophozoites confirmed that the cysteine-rich domain was located extracellularly. The location of individual epitopes was fine mapped by constructing carboxy-terminal deletions in the cysteine-rich region of the fusion protein. The locations of adherence-enhancing and -inhibiting epitopes were partially distinguished, and the epitopes where complement-inhibitory MAbs bound were demonstrated to be near the adhesin's area of sequence identity with the human complement inhibitor CD59.

Physical map of the chromosome of Neisseria gonorrhoeae FA1090 with locations of genetic markers, including opa and pil genes.

A physical map of the chromosome of Neisseria gonorrhoeae FA1090 has been constructed. Digestion of strain FA1090 DNA with NheI, SpeI, BglII, or PacI resulted in a limited number of fragments that were resolved by contour-clamped homogeneous electric field electrophoresis. The estimated genome size was 2,219 kb. To construct the map, probes corresponding to single-copy chromosomal sequences were used in Southern blots of digested DNA separated on pulsed-field gels, to determine how the fragments from different digests overlapped. Some of the probes represented identified gonococcal genes, whereas others were anonymous cloned fragments of strain FA1090 DNA. By using this approach, a macrorestriction map of the strain FA1090 chromosome was assembled, and the locations of various genetic markers on the map were determined. Once the map was completed, the repeated gene families encoding Opa and pilin proteins were mapped. The 11 opa loci of strain FA1090 were distributed over approximately 60% of the chromosome. The pil loci were more clustered and were located in two regions separated by approximately one-fourth of the chromosome.

Pathogenic and nonpathogenic strains of Entamoeba histolytica can be differentiated by monoclonal antibodies to the galactose-specific adherence lectin.

Entamoeba histolytica infection results in either asymptomatic colonization or invasive colitis and liver abscess. E. histolytica isolates from patients with invasive disease have characteristic isoenzyme profiles (pathogenic zymodemes), suggesting a role for parasite factors in determining the severity of infection. A galactose-specific cell surface lectin from a pathogenic zymodeme was shown to mediate in vitro adherence to human colonic mucins and contact-dependent killing of target cells. Six nonoverlapping antigenic determinants were identified on the 170-kilodalton heavy subunit of the pathogenic lectin. Anti-lectin monoclonal antibodies (MAb) directed against epitopes 1 and 2 enhanced adherence whereas MAb to epitopes 3 through 6 either inhibited or had no effect on adherence. We tested 50 pathogenic and nonpathogenic strains for reactivity to these anti-lectin MAb by radioimmunoassay. MAb to epitopes 1 through 6 reacted in the radioimmunoassay with all 16 pathogenic zymodeme strains tested. In contrast, only MAb to epitopes 1 and 2 bound to the lectin from nonpathogenic strains. Western immunoblots with anti-lectin antibodies showed that the 170-kilodalton heavy subunit was present in the nonpathogenic amebae. Adherence of the nonpathogenic SAW 760 strain to human erythrocytes was enhanced by MAb to epitope 1 and blocked by galactose, confirming the presence of a functionally active lectin. A lectin radioimmunoassay based on MAb to epitopes 1 and 3 proved to be a simple and rapid method to distinguish pathogenic from nonpathogenic amebae in culture. Further exploration of the functional consequences of the antigenic differences demonstrated for the lectin may lead to a better understanding of its role in pathogenesis.

Monoclonal antibodies directed against the galactose-binding lectin of Entamoeba histolytica enhance adherence.

The Entamoeba histolytica galactose-binding lectin is a surface glycoprotein composed of 170- and 35-kDa subunits. Inhibition of this lectin with galactose or anti-170 kDa subunit polyclonal antibody blocks amebic adherence to target cells and colonic mucin glycoproteins. We describe the properties of 10 mAb with specificity for the 170-kDa subunit. Based on competitive binding studies, six nonoverlapping antigenic determinants on the lectin were identified. The effect of the mAb on adherence of amebic trophozoites to both Chinese hamster ovary (CHO) cells and human colonic mucins was measured. Antilectin antibodies directed against epitopes 1 and 2 enhanced adherence, with the number of amebae having at least three adherent CHO cells increasing with the addition of epitope 1 mAb from 26 +/- 9 to 88 +/- 2% and the binding of colonic mucins increasing from 34 +/- 1 to 164 +/- 3 pg/10(5) amebae. Antibody-enhanced adherence remained 90 to 100% galactose inhibitable, occurred at 4 degrees C and was not Fc mediated. Univalent Fab fragments of epitope 1 mAb augmented mucin binding by 238% and CHO cell adherence by 338%. The binding of purified lectin to CHO cells was increased from 1.1 +/- 0.1 to 2.4 +/- 0.3 ng/10(3) CHO cells by mAb directed to epitope 1, demonstrating that enhanced adherence was due to direct activation of the lectin. mAb to epitope 3 bound to the lectin only upon its solubilization from the membrane and had no effect on adherence. Adherence to CHO cells and mucins was inhibited from 50 to 75% by mAb to epitopes 4 and 5; epitope 6 mAb inhibited amebic adherence to CHO cells but not mucins. The pooled sera from 10 patients with amebic liver abscess blocked the binding to the 170-kDa subunit of mAb directed to all six epitopes. Striking individual variations in the effects of immune sera on adherence were observed. Although the sera of all 44 South African patients with amebic liver abscess had high titer anti-lectin antibodies, 16 patients' sera significantly (more than 3 SEM) enhanced adherence whereas 25 patients' sera significantly inhibited adherence. Antilectin antibodies exert profound functional effects on the interaction of E. histolytica with target cells and human colonic mucins. Exploration of the clinical consequences of adherence-enhancing and inhibitory antibody responses may give insight into the role of antilectin antibodies in immunity to invasive amebiasis.