Cellular sensitivity in amoebiasis--preliminary results of lymphocytic transformation in response to specific antigen and to mitogen in carrier and disease states

Immunopathology of Entamoeba histolytica infections

Entamoeba histolytica infects almost 10% of the world's population and results in about 100 000 deaths annually(1). Relatively little information is available concerning the immune response and the immunopathology elicited by this parasite, probably due in part to the lack of a truly appropriate animal model(2-4). However, there has been some progress - particularly concerning the interaction of this parasite with cells of the immune system(5,6). This review summarizes the salient features of the cellular immune response and immunopathology, largely from in vitro studies and studies using the gerbil model for invasive amoebiasis(7,8). Overall, the results suggest that invasive amoebtasis induces profound immune dysfunction both at the effector level of macrophages and on their accessory cell potential.

T-cell suppression and selective in vivo activation of TH2 subpopulation by the Entamoeba histolytica 220-kilodalton lectin

A 220-kDa surface protein (L220) with lectin activity from Entamoeba histolytica trophozoites has been characterized previously (J. L. Rosales-Encina, I. Meza, A. López-de-León, P. Talamás-Rohana, and M. Rojkind, J. Infect. Dis. 156:790-797, 1987). This molecule is involved in the adhesion process (I. Meza, F. Cázares, J. L. Rosales-Encina, P. Talamás-Rohana, and M. Rojkind, J. Infect. Dis. 156:798-805, 1987) and is very immunogenic. In this work, we studied both the humoral and the cellular immune responses to L220. We compared L220 with L220-derived components, such as a fusion peptide (M-11) and chemically obtained peptides (by treating the 220-kDa molecule with N-chlorosuccinimide-urea). Spleen cells from L220-immunized mice were unable to proliferate in vitro when stimulated with the protein. However, a proliferative response was obtained when mice were immunized with the L220-derived fusion peptide or the cleaved lectin. To find out if there was a correlation between the observed responses and TH1 or TH2 activation, we analyzed patterns of cytokine secretion (interleukin-2 [IL-2], IL-4, IL-10, and gamma interferon). Cells from mice immunized with peptides that induced cell proliferation (100, 80, and 47 kDa) with the peptides (P < 0.01) and with the intact molecule secreted IL-2 and gamma interferon, showing a TH1-subset pattern. Conversely, cells from mice immunized with the intact 220-kDa molecule secreted IL-4 and IL-10, typical of a TH2 subpopulation; however, antibodies from each group recognized the 220-kDa molecule as determined by Western blotting (immunoblotting). These results suggest that various epitopes in the 220-kDa molecule generate different response patterns, suppressing or activating T-cell responses.

Intestinal amebiasis: cyclic suppression of the immune response

The cellular immune response was evaluated in a C3H/HeJ mouse model of intestinal amebiasis at 5-60 days postinoculation with Entamoeba histolytica. At various intervals, spleen lymphocytes were obtained from infected and noninfected control mice and cultured with concanavalin A (Con A), pokeweed mitogen (PWM), or ameba antigen. E. histolytica infection induced a cyclic depression of DNA synthesis when spleen lymphocytes were stimulated with a T-cell mitogen (Con A), a T- and B-cell (PWM) mitogen, or an ameba antigen. A similar response was observed in the determinations of interleukin-2 in the supernatants of Con A-stimulated spleen cells from infected mice. When spleen cells from E. histolytica-infected mice were stimulated with phorbol myristate acetate plus ionomycin, results indicated a signal-transduction defect. These alterations, observed at the cellular level, might facilitate invasion of the host by the parasite.

Down-regulation of murine lymphocyte responsiveness to mitogens after treatment with antigens of Entamoeba histolytica

Injection of mice with pathogenic Entamoeba histolytica (strain HM1-IMSS) antigens resulted in a decreased capacity of splenocytes to respond to mitogen-induced blastogenesis following a challenge with concanavalin A (Con A), phytohemagglutinin (PHA), and lipopolysaccharide (LPS), whereas no inhibition was observed in mice that had previously been injected with equivalent amounts of non-pathogenic E. histolytica-like Laredo antigens. Depletion of adherent cells in the splenocyte preparation indicated that these cells were not a major contributor to the observed immunosuppression. Quantification of splenic T-lymphocyte subsets demonstrated a significant decrease in Thy-1+ and Lyt-1+ cells, but Lyt-2+ cells were not affected. Splenocytes treated with pathogenic amoebic antigens in vitro affected the capacity of these cells to respond optimally to Con A- and LPS-induced blastogenesis but not to that induced by PHA. These findings demonstrate that amoebic antigens affect lymphocyte function and may be important co-factors in the immunoregulation and pathogenesis of amoebiasis.

Detection of IgG, IgA, IgM and IgE antibodies in invasive amoebiasis in endemic areas

Entamoeba histolytica-specific serum IgG, IgA, IgM and IgE antibodies were assayed in cases of amoebiasis in an endemic area. Patient groups consisted of amoebic liver abscess (n = 18), preabscess hepatic amoebiasis (n = 22) and amoebic colitis (n = 30). Control subjects comprised 26 asymptomatic cyst passers, 13 giardiasis cases, 20 typhoid patients and 24 non-amoebic individuals. Serum IgG was assayed by ELISA, using a monoclonal anti IgG beta-galactosidase (IgG beta-gal) conjugate, a polyclonal avidin biotin horse radish peroxidase (AB-HRP), and a polyclonal anti IgG horse radish peroxidase (IgG HRP) conjugate. IgA and IgM were assayed by the beta-gal ELISA and IgE by AB-HRP. Diagnostically significant IgG and IgA while lower IgM and IgE antibody levels were seen in extraintestinal cases. About 40% of suspected pre-abscess hepatic amoebiasis cases were confirmed by antibody estimation. All isotype levels in most dysentery cases were in the range of the controls.

Delayed-type hypersensitivity to Entamoeba histolytica in mice and hamsters: a comparison

Delayed-type hypersensitivity (DTH) to live or fixed Entamoeba histolytica was induced and compared in mice and hamsters. Peak reactions were obtained 24 h post-challenge. In mice, challenge with 10(5) amoebae produced maximal, specific footpad swelling; in hamsters, 5 x 10(4) were required. Elicitation of DTH in mice was strongest 1 week after induction and remained comparatively high for 8 weeks. In hamsters, elicitability declined after 1-2 weeks. Cyclophosphamide increased footpad reactions in mice and hamsters when given 1 day prior to induction but not prior to challenge. Reactions were usually somewhat (but not significantly) stronger in mice than in hamsters, which was also evident from adoptive transfer experiments. Thus, differences in cell-mediated immunity as expressed by DTH in mice and hamsters do not explain the differential susceptibility of these animals to infection with this parasite. In hamsters, multiple footpad injections of live or fixed amoebae lowered the percentage of subsequent liver infections after i.p. injection of virulent amoebae.

The significance of parasitic infections in terms of clinical disease: a personal view

Throughout the world, infection with parasites is extremely common. Prevalence is highest in the warm countries of the tropics and subtropics, but infection occurs in all climatic zones. The figures usually quoted for the prevalence of specific parasites attain values akin to those used to describe astronomical distances. The World Health Organization (1985) estimated that some 2582 million of the earth's inhabitants live in areas where they risk contracting malaria and that many – in Africa south of the Sahara alone probably 200 million – remain chronically and persistently infected. Estimates for other parasites are similarly impressive; 600 million at risk of infection with schistosomiasis, with some 200 million actually infected; 900 million exposed to lymphatic filarial parasites, with some 90 million currently infected; for onchocerciasis, probably some 40 million cases spread throughout Africa, Central and South America and the Eastern mediterranean. Yet, impressive as these estimates may be, they are dwarfed by those for some intestinal helminths. Recent assessments suggest that 1 person in 4 of the world's population carriesAscaris lumbricoides(Schultz, 1982), while the same proportion is believed to be infected with one or other of the hookworms (Gilman, 1982).

In vitro and in vivo interaction between trophozoites of Entamoeba histolytica and gerbil lymphoid cells

The in vitro and in vivo antiamoebic cytotoxic effects of peritoneal exudate cells and mesenteric lymph node lymphocytes of gerbils with cecal amoebiasis or those immunized with amoebic extract were investigated. A differential effect of the lymphoid cells against trophozoites of nonpathogenic and pathogenic strains of Entamoeba histolytica was observed. Nonpathogenic amoebae were more susceptible to killing by lymphoid cells than pathogenic amoebae in vitro and in vivo in infected or immunized animals. These data suggest that during the course of cecal amoebiasis in gerbils, a differential stimulation or depletion of cytotoxic cells in the lymphoreticular tissues occurs, resulting in an impaired cell-mediated immune response.

Interaction of human leukocytes and Entamoeba histolytica. Killing of virulent amebae by the activated macrophage

Capable effector mechanisms in the human immune response against the cytolytic, protozoan parasite Entamoeba histolytica have not been described. To identify a competent human effector cell, we studied the in vitro interactions of normal human polymorphonuclear neutrophils, peripheral blood mononuclear cells (PBMC), monocytes (MC), and MC-derived macrophages with virulent axenic amebae (strain HMI-IMSS). Amebae killed neutrophils, PBMC, MC, and MC-derived macrophages (P less than 0.001), without loss of parasite viability. The addition of heat-inactivated immune serum did not enable leukocytes to kill amebae, nor did it protect these host cells from amebae. MC-derived macrophages, activated with lymphokine elicited by the mitogens conconavalin A, phytohemagglutinin, or an amebic soluble protein preparation (strain HK9), killed 55% of amebae by 3 h in a trypan blue exclusion assay (P less than 0.001); during this time, 40% of the activated macrophages died. Lysis of amebae was confirmed using 111Indium oxine radiolabeled parasites and was antibody independent. Macrophage death appeared to be due to the deleterious effect of lysed amebae rather than the contact-dependent effector mechanisms of E. histolytica. Adherence between activated macrophages and amebae was greater than that between other leukocytes and amebae (P less than 0.001). Microscopic observations, kinetic analysis of the killing of amebae by activated macrophages, and suspension of amebae with adherent activated macrophages in a 10% dextran solution indicated that contact by activated macrophages was necessary to initiate the killing of amebae. Catalase but not superoxide dismutase inhibited the amebicidal capacity of activated macrophages (P less than 0.001). However, activated macrophages from an individual with chronic granulomatous disease were able to kill amebae, but not as effectively as normal cells (P less than 0.01). In summary, activated MC-derived macrophages killed virulent E. histolytica trophozoites through a contact-dependent, antibody-independent mechanism involving oxidative-dependent and -independent processes.

Human amoebiasis: the interaction of lymphocyte surface-bound immune complexes and PMNs impairs T cell proliferative responses to E. histolytica mitogen

In some of the sera from patients with amoebiasis circulating immune complexes are present which are thought to interact with lymphoid cells, enabling them to elicit a burst of oxygen consumption in PMNs. The intensity of chemiluminescence is related to the presence of C3+ and Fc IgG+ cells in the lymphoid cell suspensions employed. The generation and release of highly reactive oxygen derivatives from PMNs impair T lymphocyte proliferative responses to the E. histolytica mitogen. The Authors suggest that one of the mechanisms by which circulating immune complexes present in the sera of patients with amoebiasis may interfere with T cell-mediated immune responses, is through their binding to the surface of the C3+, Fc IgG+ cells with subsequent stimulation of the PMN oxidative metabolism.

Lymphocyte subpopulations transformation studies in an experimental model of intestinal and hepatic amoebiasis

The lymphocyte subpopulations in peripheral blood and blast transformation were studied on days 0, 3, 7, 11, 15, 20 and 35 after infection in progesterone-treated guinea-pigs which had been experimentally infected with Entamoeba histolytica by intracaecal inoculation. In animals with intestinal infection, lowered T cell numbers and blast transformation were seen during the acute phase with a subsequent tendency to recover. In guinea-pigs with hepatic amoebiasis, both these parameters were significantly depressed throughout the period of study with no tendency to recovery. In progesterone-treated and sham-operated animals, a less marked depression of T cells, was observed. The B cell population did not vary greatly in either group. This study has thus shown that in hepatic amoebiasis there is highly significant depression in both number and function of T cells in comparison to intestinal amoebiasis.

Cell-mediated immunity in hepatic amoebiasis

Cell-mediated immunity (CMI) was measured by blastic transformation of peripheral blood lymphocytes in 26 patients with amoebic liver abscess (ALA) and matched control subjects with no demonstrable clinical amoebiasis. During active disease, the mean mitogenic response, measured by the stimulation index of the patients' lymphocytes to Entamoeba histolytica antigen, was increased (mean +/- SD: 25.98 +/- 46.62 compared with 11.27 +/- 21.39), whereas that to phytohaemagglutinin (PHA) was reduced (54.80 +/- 56.26 compared with 111.70 +/- 70.61). Both these results were statistically significant (P less than 0.01); they do not, however, appear to be due to a quantitative defect in T-cell numbers, as both total peripheral lymphocytes (3332 +/- 1450 cells/microliters compared with 2447 +/- 531 cells/microliters) and T-cells (2652 +/- 1128 cells/microliters compared with 1908 +/- 386 cells/microliters) were significantly elevated in the patients (P less than 0.01). When these tests were repeated two months later in 12 cured patients they were found to be comparable to those of the control subjects. The results indicate that there is a transient cellular sensitization to amoebic antigen together with an increase in T-lymphocytes and an impairment of the mitogenic response of lymphocytes to PHA. The significance of these findings is discussed.

Increased macrophage migration inhibition factor production in hamsters sensitized by amoebic antigen and glucan

Well defined cell-mediated immune responses were detectable following experimental immunization of hamsters with Entamoeba histolytica antigen, using glucan as an adjuvant. Peritoneal cells from amoeba antigen-glucan sensitized animals, upon incubation with specific antigen in vitro, were found to release into the supernatant a macrophage migration inhibition factor (MIF). Such supernatant fluids inhibited the migration of macrophages from non-sensitized hamsters. The production of MIF was found to be greatly increased if glucan is added to amoeba antigen when sensitizing animals. The optimal concentration for maximum inhibition was recorded at 10(-8) dilution of the supernatant.

Serological differentiation between past and present infection in hepatic amoebiasis

The indirect fluorescent antibody (IFA) test and the amoebic gel diffusion (AGD) test were assessed as tools for differentiating between past and present infection in invasive amoebiasis; in the case of the IFA test the Entamoeba histolytica-specific IgG and IgM were monitored. In a pilot study in which sera from 56 patients with suspected invasive amoebiasis were tested the IgM was positive in 40% of confirmed intestinal and 83% of confirmed hepatic cases, the IgG and AGD were positive in all confirmed cases. A subsequent study was then carried out, in which the tests were used to monitor longitudinally antibody levels of patients with confirmed amoebic liver abscess, from the time of admission to hospital, to one year after successful treatment. The specific IgM levels became negative sooner than the IgG or AGD, with more than half the subjects giving negative results at six months and all cases becoming negative 46 weeks after treatment. The results of this study suggest that the presence of specific IgM, together with specific IgG and a strongly positive AGD test, is indicative of an active infection; conversely, when the IgM is negative, while the other tests are positive, active disease was usually absent.

Anti-Ia reactivity in sera from subjects with Entamoeba histolytica infection

Sera from 15 patients with Entamoeba histolytica infection were tested for anti T-cell antibodies by assessing cross-reacting specificities with the antigens defined by an anti-Ia hybridoma antibody. T cells prepared by sheep erythrocyte rosetting were preincubated with the test sera and then with the anti-Ia antibody. Binding of the specific monoclonal antibody was assessed by rosetting with ox erythrocytes conjugated with goat anti-mouse IgG. Eight sera from amoebic patients were found to block the binding of monoclonal mouse hybridoma anti Ia-antibody to T cells. Blocking of anti-Ia binding was not due to Fc IgG receptor binding by immune complexes nor was it HLA-DR restricted. T cells pre-treatment with the amoebic sera positive for anti-Ia activity showed reduced activity when tested in the autologous mixed lymphocyte reaction (AMLR). The results of our study seem to suggest the existence of specific anomalies of immunoregulation during E. histolytica infection which may play a role in inducing immune disregulation in vivo.

Application of the leucocyte adherence inhibition test to the assessment of cell mediated immunity in invasive amoebiasis

The leucocyte adherence inhibition (LAI) test was assessed as a means for measuring specific cell mediated immunity (CMI) in invasive amoebiasis. The LAI test and the amoebic gel diffusion (AGD) test were performed on 20 patients admitted to hospital with amoebic liver abscess (ALA) and 24 control subjects with no demonstrable clinical amoebiasis. The AGD results were acceptable for such a study in an endemic area as all the proven ALA subjects gave positive responses while all except one of the controls gave a negative reaction. A percentage adherence in the LAI test of more than 80% was considered to be negative and the mean percentage adherence of leucocytes for the control subjects was found to be 86.0 +/- 4.9 while that for the experimental group was found to be 76.1 +/- 15.4; the difference between these groups is statistically significant. It was noticed that the LAI test response was possibly linked with severity of disease in the ALA subjects. The LAI test has been found to be a relatively rapid test of specific CMI and although fastidious, it does not require the use of radio-isotopes.

Immunosuppressive effect of Entamoeba histolytica extract on hamsters

The immune response to sheep red blood cells (SRBC) in mice and hamsters injected with an extract of entamoeba histolytica was studied. Both the primary and secondary immune response, measured by anti-SRBC antibody titers, were unaltered in the mouse, while a significant depression of the primary, but not the secondary, response was observed in the hamster. The effect was greatest when the amebic extract (AE) and SRBC were injected on the same day. The number of anti-SRBC rosettes formed in the spleen cells of hamsters treated with both AE and SRBC on day 0 was measured from days 1-16. The response peaked on day 13, while cells from animals injected with SRBC alone gave a maximal response on day 5. The formation of anti-SRBC rosettes in T-lymphocyte-enriched spleen cells treated with anti-gamma globulin serum and complement was almost abolished for the duration of the experiment. It is suggested that the mechanism responsible for this immunosuppressive phenomenon could involve early interference in the afferent limb of the immune response.

In vitro amoebicidal activity of immune cells

The amoebicidal activity of peripheral blood lymphocytes and spleen and peritoneal cells from hamsters vaccinated against or protected from hepatic amoebiasis and from those with hepatic amoebiasis was investigated. Peripheral blood lymphocytes and peritoneal and spleen cells from vaccinated or protected animals can kill trophozoites of Entamoeba histolytica in vitro. In contrast, spleen cells from infected hamsters showed no significant cytotoxic effect on the parasite. These data suggest that cellular immunity plays an important role in host defense against hepatic amoebiasis.

Effect of specific and non-specific prior sensitization on the outcome of amoebic infection

Guinea-pigs were sensitized with monoaxenic amoebic antigen (Group I), bacterial associate antigen (Group II) and axenic amoebic antigen (Group III). All animals in Group I, 95% in Group II and 70% in group III, developed caecal lesions on intra-caecal inoculation of Entamoeba histolytica trophozoites; 92.8% of control (unsensitized) animals developed lesions in their caeca. Lesions were more severe in sensitized animals than in controls. Hepatic abscesses were found in 7.6% of group I, 11.1% of group II and 7.1% of group III. No animal from the untreated but infected group developed hepatic abscess. It thus appears that specific (amoebic) and non-specific (bacterial) prior sensitization may render the host more susceptible to hepatic amoebic infection.

Virulence of Entamoeba histolytica in rat and its comparison with the serological responses of the amoebic patients

The virulence of 70 isolates of Entamoeba histolytica was studied in the Wistar strain of albino rat by intracaecal inoculation of amoebae. The results were evaluated by the Neal scoring system, histopathological grading of ulcers and virulence indices. It was found that isolates from acute amoebic cases could infect and produce ulcers in significantly more animals than could the isolates from asymptomatic cyst passers. The virulence indices of isolates from acute cases were also significantly higher as compared to those from asymptomatic cyst passers. However, there was no significant difference between virulence indices of isolates from acute cases and non-dysenteric amoebic colitis. This study also showed that Neal scores failed to correlate with the type of pathology produced by the amoebae in the caecum. It is felt that virulence indices which depend upon the histopathological lesions should also be taken into consideration. The serological response of the patients tended to correlate with the virulence indices of isolates but only minimally. The results thus contradict a common belief amongst clinicians that higher levels of anti-amoebic antibodies reflect severe disease, as compared to low levels of antiamoebic antibodies.

Specific anti-amoebic immunoglobulins and the cellulose acetate precipitin test in Entamoeba histolytica infection

Using the indirect fluorescent antibody test and sera from 10 proved cases of invasive amoebiasis, the effects of absorption of IgG on observed titres of amoeba-specific IgM and IgA were investigated. In addition, results of cellulose acetate precipitin tests were compared with anti-amoebic antibody levels. Antiamoebic IgM was found at titres of 1:14 to 1:112 after IgG absorption in four cases. Anti-amoebic IgA was detected in sera from four cases, but the maximum titre was 1:28. There was no relationship between the presence of amoeba-specific IgM or IgA and the result of the precipitin test, but a raised anti-amoebic IgG level was consistently found where the precipitin test was positive. However, sera with raised amoeba-specific IgG levels did not invariably give a positive precipitin reaction.

Protective effects of crude and chromatographic fractions of axenic Entamoeba histolytica in guinea-pigs

Axenic amoebic antigen was chromatographed on Sephadex G-200. Two peaks divided into three fractions were obtained which were concentrated by lyophilization. Guinea-pigs were given a series of subcutaneous injections of crude Entamoeba histolytica antigen and its chromatographic fractions mixed with Freund's complete adjuvant. After three immunizing doses, the animals were challenged with intracaecal injection of a virulent isolate of amoebae (Strain No. H-25) and were killed seven days later. The antibody response was studied by indirect haemagglutination (IHA) and counter-current immunoelectrophoresis (CIEP) before intracaecal inoculation and at the time of killing. Fraction I, which had the highest molecular weight, stimulated high levels of antibodies in guinea-pigs and showed 92% protection. Only one animal of 12 inoculated had gross lesions and these were very mild. The caecal contents of three of the 11 animals without gross lesions were positive for amoebae but no tissue invasion was observed. Partial protection was observed with other antigens--30% with whole amoebae, 18% with Fraction II and 30% with Fraction III. In most there were multiple ulcers of the deep penetrating type and amoebae either penetrating and invading the muscular layer or the lytic process extending up to the muscular layer. In one animal, immunized with whole amoebic antigen, multiple hepatic lesions were also observed and trophozoites of E. histolytica were demonstrated histologically.

Hepatic amoebiasis in immunodepressed mice

The effects of immunodepression on intestinal amoebic lesions produced by Entamoeba histolytica were studied in inbred mice of the C3H/mg strain. Immunodepression was induced in two ways by giving (i) cyclophosphamide and (ii) anti-mouse lymphocyte serum. On immunodepression with the latter, although there was no difference in the degree of macroscopic intestinal damage, all five surviving immunodepressed mice showed hepatic lesions. It is noted that these had a striking histological resemblance to human and hamster lesions in hepatic amoebiasis.

A micro-method for the study of in vitro lymphocyte transformation to specific antigens

A quantitative method for studying blast-transformation of cultured lymphocytes in the presence of specific antigens is described. The technique is performed in 0.3 ml microtrays, using 2.5 X 10(5) lymphocytes per culture, with an optimal culture period of 6 days. Cultures are pulsed for 4 h with [3H]-thymidine, giving maximum incorporation and minimum cellular damage. The study also describes some disadvantages of using lymphocyte responses to phytohaemagglutinin (PHA), as a marker of T-cell function. Experiments to establish ideal conditions for each stage of the method are described. The technique can be adjusted to accommodate different antigens, cell types and for the study of animal as well as human lymphocytes.

The epidemiology of infection with Entamoeba histolytica in the Gambia, West Africa

A country-wide stool survey of The Gambia showed the prevalence of Entamoeba histolytica cysts to range from 13.7% up-country in the dry season to 52.3% near the coast. A longitudinal survey showed a near 100% infection rate over one year and a sharp rise in prevalence as the rains commence with an equally sharp fall as the rains progress. Specific antibody levels are elevated and reasonably constant through the year. Carriers generally show no specific lymphocyte reactivity to amoebic antigen but consistently parasite-negative individuals tended to show elevated lymphocyte reactivity. Attempts to discover the presence of cysts in the environment of villages by cultivation of specimens of water, soil, food, flies and washing from clothes and hands generally failed though E. histolytica was recovered once from a well.