Cell-mediated immunity in hepatic amoebiasis

Survival strategies of Entamoeba histolytica: Modulation of cell-mediated immune responses

Tissue invasion and disease associated with the protozoan Entamoeba histolytica has long been connected with suppression of host cellular immunity. Dampening of the host's defences may facilitate survival of amoebae in extraintestinal sites and development of the characteristic amoebic abscesses. In recent years, several studies have begun to clarify, at the cellular level, the specific effects E. histolytica has on immune cell accessory and effector cell functions. Here, Darren Campbell and Kris Chadee discuss the parasite's multiple modulatory effects on macrophages and T cells and how this manipulation of immune defences may enable the parasite to remain viable in the host. They suggest the putative amoebic molecules involved and potential modulation by the cytokines: interleukins IL-4 and IL-10 and transforming growth factor-beta.

Hematological effects of Blastocystis hominis infection in male foreign workers in Taiwan

Blastocystis hominis found in stool specimens has been the most frequently identified parasite among foreign workers from Southeast Asia in Taiwan since 1992. The prevalence of B. hominis was 14.1% in this study. In their quarantine physical examinations, 121 male Thai workers were examined hematologically and screened for stool parasites using the merthiolate-iodine-formaldehyde concentration method. Hematological values were compared in workers with and without a B. hominis infection. Multiple regressions were used to adjust for age. Those infected with any parasite other than B. hominis were excluded from further analysis. The workers infected with B. hominis had a lower leukocyte count (6.5+/-0.4 X 10(3)/microl) than those who were not (7.4+/-0.2 X 10(3)/microl). This was mainly caused by a reduced neutrophil count (3.2+/-0.4 vs 4.2+/-0.2 X 10(3)/microl). Hemoglobin (13.9+/-0.3 vs 14.5+/-0.1 g/dl) and hematocrit (41.4+/-0.6 vs 42.9+/-0.2%) were also reduced in B. hominis-positive workers.

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.

[Studies on the cell-mediated immunity in experimental Naegleria spp. infections]

Observations were made on the differences in cell-mediated immune responses in the mice infected with strongly pathogenic Naegleria fowleri ITMAP 359, weakly pathogenic Naegleria jadini 0400, or non-pathogenic Naegleria gruberi EGB, respectively. Variations in cell-mediated responses and changes in antibody titers according to the duration after infection were noted. Infections were done by dropping 5 microliters saline suspension containing 10 x 10(4) trophozoites cultured axenically in the CGVS medium into the right nasal cavity of ICR mice aging about 6-7 weeks, under the anesthesia by intraperitoneal injection of secobarbital. Following infection, delayed type hypersensitivity(DTH) responses in the footpad and blastogenic responses of the mouse spleen cells using [3H]-thymidine were observed on the day 1, 4, 7, 10 and 14 after infection. For the preparation of amoeba lysates, each of cultured trophozoites were homogenized with an ultrasonicator, and centrifugated at 20,000 g. The supernatants of amoeba lysates were used as the mitogen and antigen for ELISA. Concanavalin A(Con. A) and lipopolysaccharide(LPS) were also used as mitogens in the blastogenic response. 1. The mice infected with N. fowleri showed the mortality rate of 75.7%. The rate was 6.2% for the N. jadini infected group, while no dead mouse was observed for N. gruberi infections. 2. In regard to DTH responses in the N. fowleri infected mice, the level increased in comparison to the control group but declined after 7 days. An increase was also noted for the N. jadini group after 1 day, but gradual decreases were observed through the infection period. In addition, no difference was noted between the N. gruberi infected and control groups. 3. Concerning the blastogenic response of the splenocytes, it increased after 10 days in the experimental group of N. fowleri infection, but the differences were not statistically significant compared with control group. It was evident that N. jadini group was not different from control group either, while there was a tendency of decrease in N. gruberi infected group. In regard to the blastogenic response of the splenocytes by LPS, it was found that the N. fowleri, N. jadini and N. gruberi infected groups had no differences from the control group. 4. The serum antibody titer of N. fowleri and N. jadini infected mice increased from the day 7 and 14 after infection respectively, while the N. gruberi infected mice showed no increase.(ABSTRACT TRUNCATED AT 400 WORDS)

[Cell-mediated immunity in experimental amoebic meningoencephalitis]

Cell-mediated and humoral immune reactions in mice infected with pathogenic Acanthamoeba culbertsoni were observed according to the period of time after amoebic infection by intranasal inoculation. The degrees of blastogenesis of spleen cells induced by mitogens, which were measured using radioactive [3H]-thymidine, were compared between infected and non-infected control groups. The mitogens used in this blastogenesis experiment were concanavalin A (Con A) and lipopolysaccharide(LPS). On the other hand, enzyme-linked immunosorbent assay(ELISA) was employed for the detection of humoral antibodies against A. culbertsoni. The levels of blastogenesis of splenocytes and serum titres in the experimental group showed increasing tendency a week after inoculation of A. culbertsoni, although there was no difference between the experimental and control groups in other periods of the experimental time.

Kinetics of the immune responses during the course of hepatic amoebic infection--an experimental study

Following intrahepatic inoculation of axenic Entamoeba histolytica (strain NIH:200V), all hamsters developed amoebic abscesses in the liver by 7 d after inoculation. All the animals cleared the infection spontaneously by 28 d after inoculation. The establishment of amoebae leading to acute liver abscess was accompanied by significantly reduced levels of antibodies to the plasma membrane (PM) protein of E. histolytica, reduced direct macrophage cytotoxicity, and reduced anti-PM antibody-mediated macrophage-dependent cytotoxicity to amoebic trophozoites. This phase of infection was also accompanied by a significant reduction in cellular sensitization to PM proteins and to phytohaemagglutinin. Reduction in size of the liver abscesses and clearance of infection were accompanied by significant development of anti-PM antibodies, cellular sensitization to the PM proteins, enhanced direct macrophage cytotoxicity, and anti-PM antibody-mediated macrophage-dependent cytotoxicity to trophozoites. The data suggest that the amoebic disease process is modulated by immune responses to the PM protein of E. histolytica.

Alterations of humoral, cell mediated and antibody dependent cell mediated cytotoxic responses during the course of amoebic infection in guinea pigs

The cellular and antibody dependent cellular cytotoxic (ADCC) responses of splenic lymphocytes and peritoneal macrophages obtained from animals at variable intervals after inoculation were studied against trophozoites of axenic E histolytica (NIH:200). Cytotoxic responses of effector cells from infected animals were compared with those of effector cells from vaccine stimulated and unstimulated uninfected control animals. Cellular and antibody-dependent cellular cytotoxic responses of the effector cells from animals during the establishment and acute phase of infection were significantly suppressed, compared with unstimulated uninfected and vaccinated (FI amoebic proteins stimulated) effector cells. The effector cells from animals recovered from infection showed enhanced cytotoxic responses against trophozoites of E histolytica. The suppressed cytotoxic response was accompanied by impairment of cytotoxic cell activities and lack, or very low level of anti-FI antibodies in the sera of animals during the establishment phase of infection. With the rise in anti-FI antibodies in the sera of animals ADCC could be induced effectively against trophozoites of E histolytica, which seem to result in clearance of amoebic infection.

[Blastogenic responses of splenic lymphocytes to Naegleria fowleri lysates and T-cell mitogen in mice with primary amoebic meningoencephalitis]

This study was to observe the changes of blastogenic responses of splenic lymphocytes to T-cell mitogens, N. fowleri lysate and concanavalin A, and serum antibody titer during the course of experimental PAM in mice. Naegleria fowleri, strain 0359, was cultured in the CGVS medium axenically and inoculated intranasally with 7 x 10(4) trophozoites for the development of experimental PAM in mice. The amoebae were subjected to ultrasonication and centrifuged at 20,000 g for 60 minutes, and filtered through 0.2 micro-m filter membrane. The supernatant, N. fowleri lysate, was used as T-cell mitogen, and antigen for ELISA. The serum antibody was examined by ELISA using peroxidase conjugate. Two hundred micro-l of 10(6) splenocytes in RPMI 1640 containing 10% fetal calf serum were added to each well of a microtiter plate. To each well was added T-cell mitogens, 100 micro-g/ml of N. fowleri lysate or 4 micro-g/ml of con. A, and the plates were incubated for 42 hours at 37 C in 5% CO(2) incubator. Cultures were pulsed with 1 micro-Ci of methyl-(3H)-thymidine 6 hour before harvesting. The mean blastogenic response of the splenocytes to N. fowleri lysate was reduced, whereas that to con. A was also reduced up to on day 11 after infection. Both of these results were statistically significant compared with those of uninfected control group. The serum antibody titers were increased gradually up to day 15. The results indicated that there was an impairment of the blastogenic response of splenocytes to N. fowleri lysate during the acute course of experimental PAM in mice.