Librado Ortiz-Ortiz

How protozoan parasites evade the immune response

Protozoan pathogens such as Plasmodium, Leishmania, Trypanosoma and Entamoeba are responsible for several of the most widespread and lethal human diseases. Their successful survival depends mainly on evading the host immune system by, for example, penetrating and multiplying within cells, varying their surface antigens, eliminating their protein coat, and modulating the host immune response. Immunosuppression is sometimes caused directly by parasite products and sometimes involves antigenic mimicry, which often appears in association with parasitic diseases. However, one of the most sophisticated mechanisms of evasion is the selective activation of a subset of T helper cells.

Trypanosoma cruzi: immunosuppressed response to different antigens in the infected mouse.

Abstract Trypanosoma cruzi: Immunosuppressed response to different antigens in the infected mouse. Experimental Parasitology 45 , 190–199. Trypanosoma cruzi infection in mice results in functional changes in the normal immunological responses to heterologous antigens. An immunosuppression of the 19 and 7S antibody response is observed in infected animals against both a particulate antigen and against soluble antigens. Furthermore, the immune response to the soluble T-independent antigens, DNP-Ficoll and LPS, was also similarly impaired when antigen was administered to trypanosome-infected animals. The suppression of the immune response to these antigens does not seem to involve an alteration in the macrophage, as evidenced by a normal uptake and handling of soluble 131 I-labeled HSA and by a normal immune response when antigen-exposed peritoneal macrophages from trypanosome-infected mice were transferred to normal mice. These data support the concept that T. cruzi induces an immunosuppression to both T-dependent and T-independent antigens and that the depression observed is not due to an alteration in macrophage function.

Cell-mediated immunity in patients with amebic abscess of the liver.

Abstract Migration-inhibition factor (MIF) and delayed skin tests with axenic antigen obtained from Entamoeba histolytica were performed in 13 cases of amebic liver abscess and in 16 control individuals with no clinical or laboratory evidence of amebiasis. All subjects were of low socioeconomic condition, drawn from a community in Mexico City where amebiasis is highly endemic. Patients with amebic liver abscess revealed diminished cell-mediated immunity to E. histolytica antigen when tested by skin tests and for MIF production. Skin reactions to streptokinase-streptodornase were normal. When the same patients were tested 10 days after discharge from hospital, they all had normal delayed-type skin reactions and MIF production to E. histolytica antigen. During liver abscess as well as 10 days after successful treatment, sera from patients disclosed antibodies by counterelectrophoresis and passive hemagglutination tests. The importance of the relationship between performance of the tests and the clinical evolution of the disease is discussed.

Trypanosoma cruzi: early immune responses in infected mice.

Abstract The influence of an active Trypanosoma ( Schizotrypanum ) cruzi infection in mice and the subsequent immune response to an administered unrelated, erythrocyte antigen was studied. When mice were infected with blood forms of the parasite, a depression of the humoral immune response to injected burro erythrocytes (BE), was observed. The suppression became evident at a time when the magnitude of parasitemia and tissue forms was increasing in the sensitized and infected mice. The immunosuppressive effect induced by the infection to BE was demonstrated by a diminished direct (19S) and indirect (7S) antibody-forming cell response. Additionally, a significant increase in phagocytic activity was observed in T. cruzi -infected mice using colloidal carbon uptake experiments. Probable mechanisms of suppression are discussed and related to accepted lymphocyte activities.

Enhanced Mononuclear Phagocytic Activity during Trypanosoma cruzi Infection in Mice

It has been shown that Trypanosoma cruzi-infected mice develop a nonspecific resistance to challenge with an unrelated microorganism, namely, Listeria monocytogenes. This increased resistance to Listeria was observed on the 4th day of trypanosoma infection and persisted for at least 25 days. It was associated with an increased mononuclear phagocytic activity, as revealed by carbon clearance experiments. The possibility that macrophages of the infected host become activated by a process which appears to depend upon some form of specific interaction between the immune lymphoid cells and the infecting organisms, as has been demonstrated with other infectious agents, is discussed.

Cloning and characterization of Entamoeba histolytica antigens recognized by human secretory IgA antibodies

Abstract To identify the Entamoeba histolytica antigens capable of inducing secretory IgA (sIgA) responses in humans, a cDNA library from the strain HM1:IMSS was immuno-screened with saliva from patients with intestinal amebiasis or amebic liver abscess. Clones isolated with sIgA antibodies from patients with intestinal amebiasis corresponded to the known serine-rich protein isoform, a 29 kDa cysteine-rich protein and 1-α elongation factor. Clones corresponding to enolase, cyclophilin, ribosomal protein L23a, and an Hsp70 family protein were isolated with sIgA from a patient with amebic liver abscess. A glutamic acid-rich peptide (EhGARP) positive with sIgA from a patient with amebic liver abscess was also isolated; for EhGARP, no homologs were found in the protein databases. The antigens isolated are potentially useful in the development of an oral vaccine or new diagnostic tools for amebiasis.

Effect of zinc on Entamoeba histolytica pathogenicity

Abstract The present study analyzes the effects of zinc on Entamoeba histolytica activity and on its pathogenicity. Metal activity was evaluated in vitro with regard to the parasites viability, replication, and adhesion to epithelial cells and in vivo with regard to its pathogenicity. The results obtained in vitro show that zinc at 1.0 mM concentration does not affect amebic viability; however, it does decrease amebic replication and adhesion (P < 0.001). In vivo studies performed on a model of experimental liver abscess in the hamster indicate that the intraperitoneal administration of a single dose of zinc at 48 h after the intrahepatic inoculation of amebic trophozoites significantly inhibits (P < 0.001) abscess development. The results indicate that zinc alters the functionality of the ameba in vitro as reflected by a decrease in replication and adhesion and in vivo as manifested by inhibition of amebic pathogenicity.

Protection against murine intestinal amoebiasis induced by oral immunization with the 29 kDa antigen of Entamoeba histolytica and cholera toxin

Entamoeba histolytica antigens recognized by salivary IgA from infected patients include the 29 kDa antigen (Eh29), an alkyl hydroperoxide reductase. Here, we investigate the potential of recombinant Eh29 and an Eh29-cholera toxin subunit B (CTxB) fusion protein to confer protection against intestinal amoebiasis after oral immunization. The purified Eh29-CTxB fusion retained the critical ability to bind ganglioside GM(1), as determined by ELISA. Oral immunization of C3H/HeJ mice with Eh29 administered in combination with a subclinical dose of whole cholera toxin, but not as an Eh29-CTxB fusion, induced elevated levels of intestinal IgA and serum IgG anti-Eh29 antibodies that inhibited trophozoites adherence to MDCK cell monolayers. The 80% of immunized mice seen to develop IgA and IgG immune responses showed no evidence of infection in tissue sections harvested following intracecal challenge with virulent E. histolytica trophozoites. These results suggest that Eh29 is capable of inducing protective anti-amoebic immune responses in mice following oral immunization and could be used in the development of oral vaccines against amoebiasis.

Rapid Screening Test for Tuberculosis Using a 38-kDa Antigen From Mycobacterium tuberculosis

A screening test for the diagnosis of tuberculosis by immunodot (Idt) is described, using an antigen of Mycobacterium tuberculosis, namely, a 38‐kDa glycoprotein which has shown great specificity in previous serologic analyses. The test was used to examine 28 sera from patients with lung tuberculosis. Of these, 85% were positive by micro‐ELISA and by the Idt test herein described. Control sera from healthy subjects (n=20) gave negative results for ELISA and for Idt, which indicates that the screening test is highly specific. The test is easy to handle and requires no equipment and is therefore particularly useful for field studies. J. Clin. Lab. Anal. 12:126–129, 1998.

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 withEntamoeba 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 fromE. 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.