Passive transfer of immunity against hepatic amoebiasis in the hamster by cells

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.

Effects of Cryptosporidium muris (strain MCR) infection on gastric mucosal mast cells in mice

The responses of gastric mucosal mast cells (GMMCs) to infection with coccidian protozoa, Cryptosporidium muris, in mice were examined during primary and challenge infections. Each of three-week old ICR SPF mice was orally inoculated with a single dose of 2 x 10(6) oocysts of C. muris (strain MCR). After oocyst shedding ceased, the mice were orally challenged with a single dose of 2 x 10(6) oocysts of the same species. GMMCs reached a peak on days 20-30 postinoculation (PI) in number, and decreased thereafter. An increase on days 20-30 post-challenge-infection (PCI) was also observed. The mice showed, on the whole, normal profiles of oocyst shedding in droppings. The number of the cells of uninfected control mice remained constant. Judging from the above results, it is suggested that mastocytosis correlate with expulsion of C. muris in primary infection and the defense mechanism of challenge infection.

[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.

[Passive immunity by splenocyte transfer against amebic meningoencephalitis in mice]

The role of passive cell-mediated transfer of immunity against primary amoebic meningoencephalitis(PAME) in mice was studied. Naegleria fowleri, ITMAP 359, were cultured in CGVS medium. The ICR mice used were six week-old males of average weight of 15 g. Immunization was done by three intraperitoneal injections of l x 10(6) N. fowleri trophozoites at the interval of one week. Splenocytes were obtained from normal and immune mice spleens, and 1 x 10(7) cells were administered intraperitoneally into mice 3 days before challenge infection. Mice were infected intranasally with 7 x 10(4) N. fowleri trophozoites in a 3 microliter suspension under secobarbiturate anesthesia. Transplants of normal or immune splenocytes seem to alter the pattern of the PAME development. The splenocytes transferred from immune mice reduced the mortality rate in the N. fowleri infected mice, as compared with the mice transferred with the same number of normal splenocytes or without splenocyte. The blastogenic response of the splenocytes to both lipopolysaccharide and concanavalin A was elevated on day 7 after infection the mice transinoculated with immune splenocytes. The serum antibody titers in the mice transferred with immune splenocytes were increased gradually from day 7 up to day 20 after infections by mean of ELISA. It is suggested that the transfer of splenocytes from immunized mice conferred immunity against N. fowleri infection.

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.

Development of inflammation and augmented chemotactic responsiveness of murine peritoneal macrophages following treatment with Entamoeba histolytica trophozoites

The accumulation of inflammatory cells in the peritoneal cavity of C57BL/6 mice was examined following intraperitoneal injection of Entamoeba histolytica trophozoites. Two different strains of E. histolytica were used: a virulent strain (IP:0682:1) and a non-virulent strain (DKB). Injection of 10(6) trophozoites of either strain resulted in significant increases in the numbers of total peritoneal cells, macrophages and polymorphonuclear cells as compared to either saline-injected control mice or mice injected with 10-fold lower doses of trophozoites. The in vitro chemotactic response of macrophages from amoebae-induced exudates was also examined. Macrophages from mice treated with strain IP:0682:1 or DKB strain trophozoites were more responsive to complement-derived chemotactic factors than macrophages from saline-injected mice. This increase was significant on day 2 and persisted at enhanced levels until day 20 when the experiment was terminated. In addition, it was found that trophozoites activated normal mouse serum resulting in the production of serum-derived chemotactic activity.

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.

Role of macrophages in host defense against hepatic amoebiasis in hamsters

The role of macrophages in hepatic amoebiasis in hamsters has been investigated by means of antimacrophage serum prepared in rabbits. Animals treated with normal rabbit serum or antimacrophage serum, as well as untreated controls, were inoculated intrahepatically with 10(5) axenic trophozoites of Entamoeba histolytica. In hamsters treated with antimacrophage serum before intrahepatic inoculation of amoebae, the mean weight of the metastatic foci was significantly greater than in normal rabbit serum-treated or untreated controls. Treatment of hamsters with antimacrophage serum both before and after administration of amoebae not only increased significantly the size of the abscess in the liver but also allowed dissemination of metastatic foci to other organs.