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

Macrophage migration inhibitory factor (MIF): a key player in protozoan infections

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine produced by the pituitary gland and multiple cell types, including macrophages (Mø), dendritic cells (DC) and T-cells. Upon releases MIF modulates the expression of several inflammatory molecules, such as TNF-α, nitric oxide and cyclooxygenase 2 (COX-2). These important MIF characteristics have prompted investigators to study its role in parasite infections. Several reports have demonstrated that MIF plays either a protective or deleterious role in the immune response to different pathogens. Here, we review the role of MIF in the host defense response to some important protozoan infections.

Biochemical and immunological studies on soluble antigens of Entamoeba histolytica

The soluble antigens of Entamoeba histolytica trophozoites were analysed in detail by biochemical and immunochemical methods. The antigen was highly complex and heterogeneous as revealed by Sephacryl S-300 column chromatography, which showed four distinct fractions. The molecular mass of fractions FI, FII, FIII and FIV was 660, 170, 65 and 13 kDa, respectively. Protein was the major constituent in crude soluble antigen (CSA) and fractions FI and FII (67%, 80% and 90%, respectively). Polysaccharide was predominant in the FIII fraction (59%). Antigenic activity observed after different physico-chemical treatments revealed that CSA and FI antigens were predominantly glycoprotein in nature. However, the antigenicity of FIII antigen was greatly reduced after sodium meta-periodate treatment, whereas no alteration in reactivity was discerned after trypsin treatment. Sodium dodecyl sulphate-polyacryl-amide gel electrophoresis (SDS-PAGE) analysis demonstrated nearly 28 Coomassie blue bands for CSA and 20, 16, 15 and 3 polypeptide bands for the FI, FII, FIII and FIV fractions, respectively. The molecular mass of the polypeptides of these bands ranged from 210 to 20 kDa. Antigenic activity was observed in CSA and in the first three fractions, both in counter immunoelectrophoresis (CIEP) and in enzyme-linked immunosorbent assay (ELISA). However, the highest antigenic activity was noted in fraction FI. Major immunoreactive polypeptides of CSA and FI antigens against whole trophozoite antibody were observed in the 10- to 170-kDa regions. However, major differences in the immunoreactivity of the two antigens were noted at 116 and 14 kDa for FI antigen and at 84, 30 and 20 kDa for CSA.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of immunosuppressive and immunostimulatory treatment on experimental amoebiasis

Immunosuppressive treatments consisting of ionizing irradiation or drugs were employed in inbred and outbred mice and in golden hamsters. Following treatment, mice were challenged intracaecally or intrahepatically with virulent, axenically-grown Entamoeba histolytica. Hamsters were challenged by intraperitoneal injection of the amoebae. Many of the experimental animals died of the combined effects of treatment and challenge. Mice remained essentially refractory to infection with E. histolytica regardless of the immunosuppressive means employed. Liver infection rates in treated and control hamsters were largely similar to one another, i.e. immunosuppressive treatment had no effect on resistance to infection. Our inability to alter the susceptibility of mice and hamsters to amoebic infection by suppressing components of the immune system does not enable us to draw any clearcut conclusions as to the effect of immunosuppression on human amoebiasis. Of the various immunostimulatory materials employed in hamsters, including polysaccharides, BCG and muramyl peptides, only glucan displayed protective capacity against infection with E. histolytica, making it an effective protective agent in an extracellular parasitic infection in addition to its published effectiveness in intracellular protozoal infections. Peritoneal cells extracted from hamsters injected intraperitoneally with E. histolytica seemed capable of reducing the infectivity of virulent amoebae after coincubation in vitro, as shown by reduced infection rates in challenged hamsters. Apparently polymorphonuclear cells, which constituted the vast majority of the extracted cells 24 hours after the stimulatory injection, can, under certain conditions, diminish the infectivity of E. histolytica.

Immunization against Trypanosoma cruzi: adjuvant effect of glucan

Trypanosoma cruzi, the causative agent of Chagas' disease, infects humans and animals in tropical, subtropical and some temperature regions of the western hemisphere. At present, there is no effective vaccine for T. cruzi infection. Glucan, a beta-1,3 polyglucose biological response modifier, possesses significant adjuvant activity. The present study investigated the adjuvant activity of particulate glucan when combined with a vaccine of glutaraldehyde-killed T. cruzi culture forms. ICR/HSD mice (20 g) were injected s.c. with glutaraldehyde-killed T. cruzi on days 21, 14 and 7 prior to challenge with 50 T. cruzi blood forms. Particulate glucan (1 mg/mouse) was administered s.c. either alone or in conjunction with T. cruzi vaccine. Isovolumetric dextrose served as control. Dextrose, glucan or T. cruzi vaccine as single treatment regimens showed 100% mortality with 20.5, 21.4 and 21.6 day median survival times, respectively. In contrast, glucan administered with T. cruzi vaccine showed an 85% (P less than 0.01) survival at 275 days post-challenge. In addition, the number of T. cruzi observed in the blood of glucan--T. cruzi immunized mice was lower than the appropriate controls. However, immunized mice which survived at 275 days were positive for the presence of T. cruzi by xenodiagnosis. Histopathologic evaluation of glucan--T. cruzi mice revealed no parasites or cardiac pathology, but a mild splenic hyperplasia and inflammation of skeletal muscle were noted. In subsequent studies, mice were immunized with the same regimen of glucan--T. cruzi and challenged with 500 or 5000 T. cruzi. Glucan significantly (P less than 0.05) increased survival as denoted by 60% and 50% survival in the glucan-T. cruzi group vs 0% in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Entamoeba histolytica antigens as possible vaccinogens? A short review

A few key papers which have recently been published on the characterization of amoeba antigens are reviewed. Immunofluorescence tests and immunoelectron microscopy have demonstrated the localization of certain surface antigens on axenically cultured trophozoites. Most of the surface antigens have largely been shown to elicit a humoral response. The elicitation of cellular response has not been well illustrated. The localization of a large number of antigens in cytoplasmic vacuoles and plasma membrane indicates that a greater stimulus to the host would be provided by intracellular antigens than by those located on the surface of amoeba trophozoites. In a few inoculation studies, amoeba antigens, in combination with several adjuvants, have been successfully employed for inducing protective immunity in various animal model systems. These and other results clearly demonstrate that amoeba antigens are fully capable of generating humoral and as well as CMI responses. A combination of these two effector limbs of immunity can be fully exploited through effective use of future vaccines.

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.

Vaccination of rabbits against Entamoeba histolytica with aqueous suspensions of trehalose-dimycolate as the adjuvant

Rabbits were immunized with soluble Entamoeba histolytica antigen with an aqueous suspension of trehalose-6,6'-dimycolate used as the adjuvant. Induction of protective immunity in the immunized animals was demonstrated by enhanced humoral and cell-mediated immune responses and 100% survival after challenge. Administration of soluble antigen only failed to induce a similar degree of protective immunity. Trehalose-6,6'-dimycolate alone produced only a slight increase in nonspecific resistance.