Control of coccidiosis: lessons from other sporozoa

Coccidiosis is the most important parasitic infection in poultry worldwide and also causes problems in cattle, sheep and goats. Control is largely limited to good husbandry and prophylactic chemotherapy using a range of drugs against which resistance is rapidly acquired. Attempts at vaccination using conventional vaccines have been disappointing and there is now a need for a new approach. Research into the immunology of coccidiosis has lagged behind that of other sporozoans and there are useful lessons that might be learned from studies on toxoplasmosis, cryptosporidiosis, theileriosis and malaria. In these infections the emphasis has turned to the cytokine network that drives the response towards protection. Central to these studies are the roles of interferon-gamma, interleukin-12 and activated macrophages with the involvement of nitric oxide in parasite killing. Cytotoxic T cells have also increasingly been implicated. Research has shown that different immune responses can be elicited by manipulating the cytokine system and these new concepts can be applied to the design of peptide or recombinant vaccines, and the possibilities of developing such vaccines against coccidiosis will be discussed.

Induction of cell-mediated immunity during early stages of infection with intracellular protozoa

Toxoplasma gondii and Trypanosoma cruzi are intracellular parasites which, as part of their life cycle, induce a potent cell-mediated immunity (CMI) maintained by Th1 lymphocytes and IFN-gamma. In both cases, induction of a strong CMI is thought to protect the host against rapid parasite multiplication and consequent pathology and lethality during the acute phase of infection. However, the parasitic infection is not eliminated by the immune system and the vertebrate host serve as a parasite reservoir. In contrast, Leishmania sp, which is a slow growing parasite, appears to evade induction of CMI during early stages of infection as a strategy for surviving in a hostile environment (i.e., inside the macrophages which are their obligatory niche in the vertebrate host). Recent reports show that the initiation of IL-12 synthesis by macrophages during these parasitic infections is a key event in regulating CMI and disease outcome. The studies reviewed here indicate that activation/inhibition of distinct signaling pathways and certain macrophage functions by intracellular protozoa are important events in inducing/modulating the immune response of their vertebrate hosts, allowing parasite and host survival and therefore maintaining parasite life cycles.

Parasitic opportunistic infections in Czech HIV-infected patients--a prospective study

To determine the frequency of opportunistic parasites, especially causative agents of microsporidiosis and cryptosporidiosis in HIV-infected patients in the Czech Republic, more than 75% of all Czech HIV-infected patients were examined during this study. Target staining techniques were used for parasitological examination of stool, sputum and urine of HIV-infected patients. In addition, their sera were examined by indirect ELISA technique with specific antigens from E. cuniculi, E. hellem and C. parvum. Specific antibodies to T. gondii were detected by CF test. In 2.1% of HIV-infected patients microsporidia E. bieneusi and E. intestinalis were found by parasitological examination, 5.3% of HIV-infected patients were seropositive to E. cuniculi and 1.3% to E. intestinalis were found by parasitological examination, 5.3% of HIV-infected patients were seropositive to E. cuniculi and 1.3% to E. hellem antigens in the high titre of 600. All blood donors (control group) were seronegative in these titres. C. parvum oocysts were found in one AIDS patient, 10.5% patients were seropositive to C. parvum in higher titres (600, 1800). Occurrence of T. gondii antibodies was not significantly greater in HIV-seropositive patients (27.5%) than in the control group (21.4%). P. carinii was detected in 13.6% of the patients. This study shows the quite low occurrence of opportunistic parasitoses among Czech HIV-infected patients. Although the high prevalence of specific antibodies against causative agents of microsporidiosis and cryptosporidiosis was recorded, the number of clinical cases was low.

Complement fixing antibody production in thymectomized Oncorhynchus mykiss, vaccinated against or infected with the pathogenic haemoflagellate Cryptobia salmositica

Short-term thymectomized (two months after thymectomy) adult rainbow trout, Oncorhynchus mykiss (Walbaum) infected with the flagellate Cryptobia salmositica Katz, 1951 responded well during primary infection with C. salmositica and recovered fish also showed secondary response (rapid production of complement fixing antibody after homologous challenge) five months after recovery. Complement fixing antibody was detected during primary and secondary responses and the titres of complement fixing antibody in thymectomized fish were significantly lower than those in infected intact fish. The parasitaemia in thymectomized infected fish was significantly lower than in intact infected fish. Both recovered thymectomized fish and intact fish were protected from cryptobiosis when they were challenged. Similarly, long-term thymectomized fish (nine months after thymectomy) vaccinated with an attenuated strain of C. salmositica were protected from cryptobiosis. There were no significant difference (P > 0.05) in parasitaemia, packed cell volume and complement fixing antibody titres between vaccinated/challenged thymectomized and vaccinated/challenged intact fish. Hence, thymectomy in adult rainbow trout did not decrease the detectable complement fixing antibody against C. salmositica in long-term thymectomized fish but reduced the detectable protective antibody in short-term thymectomized fish.

Protective antibodies and anamnestic response in Salvelinus fontinalis to Cryptobia salmositica and innate resistance of Salvelinus namaycush to the hemoflagellate

Cryptobia-susceptible Salvelinus fontinalis vaccinated with a live Cryptobia salmositica vaccine were protected against C. salmositica and they were still protected 53 wk after their initial challenge. Parasites were lysed when they were incubated with immune plasma and complement and this confirms that complement-fixing antibody is an important part of the protective mechanism. Immunological memory was demonstrated in both vaccinated-challenged, and infected-recovered S. fontinalis as there were rapid and significant increases in complement-fixing antibody titers after parasite challenge. This indicates that S. fontinalis are capable of an anamnestic response. Most naive Salvelinus namaycush were not susceptible to C. salmositica infection, and their fresh plasma lysed C. salmositica under in vitro conditions. The lytic factor(s) was inactivated by heating the plasma prior to parasite incubation. This indicates that the alternate pathway of complement activation is likely the mechanism of innate resistance in S. namaycush.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.

The importance of transmission-blocking immunity in the control of infections by apicomplexan parasites

Transmission-blocking immunity may have great potential for use in the control of diseases caused by apicomplexan parasites. In this review I will describe our work on the application of transmission-blocking immunity to the control of the Eimeria parasite and compare our results to those working on transmission-blocking immunity against Cryptosporidium and Plasmodium. Eimeria causes the disease known as coccidiosis in domestic animals. Coccidiosis is particularly problematic in the chicken industry, mainly due to the crowded rearing conditions under which chicks are raised. In our work we identified, isolated and characterized 3 major gametocyte antigens (230 kDa, 82 kDa and 56/54 kDa) of Eimeria maxima. We used these native glycoproteins to immunize laying hens that, via the egg yolk, provide large amounts of transmission-blocking maternal antibodies to offspring chicks. We demonstrated that hatchlings from immunized hens shed 60-80% fewer oocysts (i.e. the infective stage of the life-cycle of Eimeria) than those from control hens. Such a reduction in oocyst output acts to significantly reduce parasite numbers in the litter of chicks raised in floor pens. This reduction in oocyst output is comparable to that seen using the most effective coccidiostat drugs and is probably sufficient to control coccidiosis under field conditions. Based on our results together with those of other groups working on transmission-blocking immunity against Cryptosporidium and Plasmodium, it appears that this immunological approach holds great promise for the control of apicomplexan parasites that cause diseases in both animals and man.

Shared themes of antigenic variation and virulence in bacterial, protozoal, and fungal infections

Pathogenic microbes have evolved highly sophisticated mechanisms for colonizing host tissues and evading or deflecting assault by the immune response. The ability of these microbes to avoid clearance prolongs infection, thereby promoting their long-term survival within individual hosts and, through transmission, between hosts. Many pathogens are capable of extensive antigenic changes in the face of the multiple constitutive and dynamic components of host immune defenses. As a result, highly diverse populations that have widely different virulence properties can arise from a single infecting organism (clone). In this review, we consider the molecular and genetic features of antigenic variation and corresponding host-parasite interactions of different pathogenic bacterial, fungal, and protozoan microorganisms. The host and microbial molecules involved in these interactions often determine the adhesive, invasive, and antigenic properties of the infecting organisms and can dramatically affect the virulence and pathobiology of individual infections. Pathogens capable of such antigenic variation exhibit mechanisms of rapid mutability in confined chromosomal regions containing specialized genes designated contingency genes. The mechanisms of hypermutability of contingency genes are common to a variety of bacterial and eukaryotic pathogens and include promoter alterations, reading-frame shifts, gene conversion events, genomic rearrangements, and point mutations.

Experimental infection of non-pregnant and pregnant sheep with Neospora caninum

In an initial experiment, 21 sheep in groups of five or six were inoculated subcutaneously (sc) with 10(8), 10(6) or 10(4) Neospora caninum tachyzoites (Liverpool isolate), or with control inoculum, and monitored for clinical signs and for "seroconversion". Animals given the two higher doses showed febrile responses and all three groups inoculated with the parasite showed seroconversion. In a second experiment, 12 pregnant sheep were each inoculated sc at 90 days' gestation with 10(6) tachyzoites, and at 25, 40 and 53 days post-inoculation (dpi) groups of four were killed for examination of the fetuses and placentas. Appropriate control ewes were included in the study. All fetuses were alive immediately before their dams were killed, except for one, which was found to be mummified at 40 dpi. Histopathological lesions were found consistently in both fetal central nervous system (CNS) and placental tissues. In the latter, focal necrosis, which was mild at 25 dpi, was much more severe at 40 dpi and much less severe at 53 dpi. Lesions in the fetal CNS consisted of focal microgliosis (with or without central necrosis), lymphoid cuffing and non-suppurative meningitis. Lesions were also found in fetal liver, heart and lung. Neospora antigen was demonstrated in fetal brain and placental tissues and, at 25 dpi, in single samples of fetal liver and heart. The prescapular lymph nodes did not differ in size from those of control fetuses but were more mature in that they contained a significantly greater number of secondary follicles. Both IgM and IgG antibodies to N. caninum were detected in the serum of fetuses from infected ewes. Thus, N. caninum readily infected pregnant ewes and caused lesions in fetal tissues and placentas which resembled those of ovine toxoplasmosis. In addition, the changes were similar to those of bovine neosporosis; the infected pregnant ewe therefore offers a good model for the bovine disease.

Of microbes, macrophages and nitric oxide

One of the most prominent functions of nitric oxide (NO) is its participation in antimicrobial and antiviral defense. This paper summarizes the evidence for this function and compiles the infectious agents which are currently thought to be controlled via high out-put generation of NO as it occurs in activated macrophages and other cells expressing the inducible isoform of NO-synthase (iNOS, NOS-2). Several less appreciated forms of interaction between NO and microbes will also be reviewed, including the role of NO as an immunosuppressive or tissue-destructive molecule during the course of infections, the regulation of microbial antioxidant systems by host cell-derived NO, the contribution of NO to parasite stage conversion, the induction or suppression of macrophage iNOS by microbial products, and the existence of endogenous NO synthase pathways in certain bacteria and parasites.

Role of natural killer cells in innate resistance to protozoan infections

Natural killer cells are now recognized as major effectors of innate resistance to protozoan parasites. The principal mechanism by which they control the growth of these pathogens is indirect, involving cytokine production rather than cytolytic activity. Recent studies have identified a series of positive and negative signals provided by cytokines and cellular interactions which regulate protozoa-induced natural killer cell function.

Immunization against parasitic diseases of fish

Parasitologists have not, in the past, exploited the immune system to protect fish against parasitic diseases. In the past few years, however, there has been an increased interest in adopting this strategy, and we have made steady and promising progress against a few parasites which are of economic importance. Amyloodinium ocellatum is an ectoparasitic dinoflagellate on brackish and marine fishes, which may also cause problems to aquarium fishes. Antiserum from fish inoculated intraperitoneally (i.p.) with living dinospores of the parasite immobilizes and agglutinates living dinospores; it also reduces parasite infectivity in cell culture. Cryptobia salmositica is a pathogenic haemoflagellate of salmonids on the Pacific coast of North America, causing mortality in semi-natural and intensive salmon culture facilities. A live attenuated vaccine inoculated i.p. protects susceptible juvenile and adult fish for at least 24 months. The protection involves production of complement fixing antibodies, phagocytosis, and antibody-dependent and antibody-independent T-cell cytotoxicity. A monoclonal antibody against a surface membrane glycoprotein (199-200 kDa is therapeutic in that it significantly reduces parasitaemias when inoculated into fish with acute disease. Ichthyophthirius multifiliis is an ectoparasitic ciliate of freshwater fishes with world wide distribution, usually causing disease when fish are stressed and/or when environmental conditions are favourable for parasite multiplication. Live theronts injected into the body cavity protect fish, and monoclonal antibodies with immobilizing activity upon parasites have been developed. There is some evidence of passive transfer of protective immunity from immune to naive fish, and to eggs. Diplostomum spathaceum is an intestinal parasite of gulls; the metacercaria stage of the parasite encyst and causes disease and mortality in numerous species of freshwater fish in Europe and in North America. Fish injected i.p. with sonicated/killed cercariae or metacercariae have fewer metacercariae in the eyes and survives longer. Lepeophtheirus salmonis and Caligus elongatus are parasitic copepods (sea lice), and they are important parasites of Atlantic salmon in cage cultures. A vaccine against fish lice is plausible, and the efficacy of about 20 candidate antigens in protecting fish is being tested.

Immunological activation markers in the serum of African and European HIV-seropositive and seronegative individuals

OBJECTIVE

The concentration of type 1 and type 2 cytokines and fibroblast-associated apoptosis-1 soluble receptor (sAPO-1/Fas) was analysed in the sera of Ugandan and Italian HIV-1-seropositive and seronegative individuals. The data were compared to determine whether the immunological status of these groups was different.

METHODS

Sixty-seven Ugandan and 30 Italian HIV-positive patients were analysed and stratified according to CD4 counts (group 1, > 500 x 10(6)/l; group 2, 200-500 x 10(6)/l; group 3, < 200 x 10(6)/l). Sera from 15 Ugandan and 11 Italian HIV-negative blood donors were also analysed. Serum concentration of type 1 cytokines [interleukin (IL)-2, IL-12, and interferon (IFN)-gamma] and type 2 cytokines (IL-4 and IL-10), and sAPO-1/Fas were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum levels of IL-2, IFN-gamma and IL-10 but not of IL-4 and IL-12, were elevated in HIV-positive group 1 and 2 Africans compared with HIV-positive Italian individuals. IL-4 was mildly augmented in HIV-positive group 3 African patients. Serum concentration of sAPO-1/Fas was reduced in HIV-positive Africans compared with HIV-positive Italian individuals. Finally, serum levels of IL-2 and IL-10 were increased and sAPO-1/Fas reduced when sera of HIV-negative African healthy controls were compared with their Italian counterparts. The ratio of type 1/type 2 cytokines was roughly 1.0 in HIV-negative African controls, and much greater than 1.0 in HIV-negative Italian controls.

CONCLUSIONS

These preliminary findings indicate that immune activation is present in African HIV infection. Furthermore, these data raise the possibility that abnormal immune activation and increased susceptibility to antigen-induced cell death is present even in HIV-negative African controls.

Characterization of isogenic carp (Cyprinus carpio L.) lines with a genetically determined high or low antibody production

Antibody production to dinitrophenyl-keyhole limpet haemocyanin (DNP-KLH) served as the immune parameter to divergently select carp (Cyprinus carpio L.) to produce high- and low-responder F1 hybrid lines. Antibody production to trinitrophenyl-lipopolysaccharide (TNP-LPS) and to DNP-KLH were similar in magnitude. By contrast, some high-responder lines were low responders to DNP-human serum albumin, and vice versa. Low-responder carp were relatively susceptible to infection with the parasite Trypanoplasma borreli. This suggested that at least one gene with a major influence on resistance differed between the two homozygous parents (69, 85) used to generate the high- and low-responder homozygous families, respectively. The isogenic lines showed no within-line variation in DNA fingerprints, but differed with respect to their MhcCyca-DAB genes.

Cell-mediated immune response and T-like cells in thymectomized Oncorhynchus mykiss (Walbaum) infected with or vaccinated against the pathogenic haemoflagellate Cryptobia salmositica Katz, 1951

T-cell-mediated delayed-type hypersensitivity (TDTH) reaction was detected in Cryptobia salmositica-infected intact and thymectomized (2 months post-thymectomy) Oncorhynchus mykiss (Walbaum). Both groups of fish showed significant induration at the site of C. salmositica antigen injection at 8, 12 and 16 weeks post-infection. A significant difference was not observed in TDTH reactions between the thymectomized and intact (control) infected fish. The total numbers of circulating leucocytes detected in infected thymectomized fish were significantly lower than those found in infected shamthymectomized fish. The numbers of T-like cells determined (using alpha-naphthyl acid esterase assay) in thymectomized fish (9 months post-thymectomy) were similar to those seen in intact fish prior to and at 4 weeks after vaccination with an avirulent strain of C. salmositica. At 2 weeks after challenge with the pathogen the numbers of T-like cells in intact vaccinated fish increased significantly (P < 0.01) and remained high for the duration of the study (15 weeks). However, in vaccinated thymectomized fish the numbers of T-like cells remained low after parasite challenge. These results suggest that thymectomy in adult rainbow trout did not lower T-cell-mediated delayed-type hypersensitivity; however, it reduced the numbers of circulating leucocytes and retarded the proliferation of T-like cells after antigenic stimulation.

Immune and inflammatory responses to reproductive tract infection with Tritrichomonas foetus in immunized and control heifers

Histopathologic changes and local antibody responses were studied in immunized and control heifers after intravaginal challenge with 10(6) Tritrichomonas foetus. Animals were given 3 intramuscular inoculations of immunoaffinity-purified superficial antigen, TF 1.17, in 2 different adjuvant combinations (incomplete Freund's adjuvant or dextran sulfate plus IFA-8 animals each) or adjuvant alone at 3-wk intervals and were challenged with T. foetus 2 wk later. Histologically, a nonsuppurative endometritis with nodular lymphoid aggregates in the stratum spongiosum was present in 9 of 24 heifers. Twice as many control heifers as immunized had moderate to severe endometritis at 10 wk and the rate of clearance of the organism was significantly faster in immunized than in control heifers. Furthermore, time of clearance was statistically correlated with severity of endometritis at 10 wk postinfection, when necropsies were done (P < 0.02). Because 9-10 wk postinfection is thought to be the critical period for determining fetal loss associated with endometritis, this correlation with early clearance is important to protection against disease. In heifers with moderate to severe infiltration of mononuclear cells in the endometrium, lymphoid nodules and some secondary follicles were detected. In the subgroup of 12 animals from which uterine secretions were collected. IgA antibody responses to antigen were detected by 6 wk in infected animals with increases in mean responses at 8 and 10 wk, but not in uninfected animals. A rationale is presented for consideration of the lymphoid nodules as a possible inductive site for this local antibody response to T. foetus.

Serological response to in vitro-shed antigen(s) of Tritrichomonas foetus in cattle

We developed a serological assay for detection of (l) an erythrocyte-adhering molecule(s) shed by the bovine venereal pathogen Tritrichomonas foetus and (II) serum antibodies to this antigen(s) in exposed cattle. Sera from exposed and unexposed cattle were tested for their ability to induce complement-mediated lysis of bovine erythrocytes that had been previously incubated overnight at room temperature in pH-adjusted supernatants of T. foetus culture media. Eight of 180 serum specimens from six groups of presumably unexposed cows or heifers showed a positive (> or = 1:2) hemolytic titer (specificity = 95.6%). Thirteen of 14 females in two experimentally infected groups showed a positive hemolytic titer following infection (sensitivity = 94%). In experimentally infected heifers, there was little correlation (r2 = 0.33) between serum hemolytic titers with respect to shed antigen and titers obtained in serum enzyme-linked immunosorbent assays in which whole T. foetus served as the antigen. Serum hemolytic titers rose 3 to 4 weeks sooner than did previously described vaginal mucus immunoglobulin G1 or immunoglobulin A titers with respect to whole-cell antigen or TF1.17 subunit antigen, respectively. Among 14 chronically infected bulls, only 6 (43%) showed a positive hemolytic titer. This study is the first, to our knowledge, to show a specific serological response in the host to an in vitro-shed antigen(s) of T. foetus and suggests a useful diagnostic test for potentially exposed herds.

The role of opsonization by antibody and complement in in vitro phagocytosis of microsporidian parasites by turbot spleen cells

We investigated the role played by opsonization by antibody and complement in in vitro phagocytosis of microsporidian spores by turbot adherent phagocytes. Most turbot adherent cells displaying phagocytic activity are probably macrophages. Phagocytosis of yeast cells and polystyrene beads was greatly enhanced in the presence of both the Ig and the non-Ig (i.e. complement-containing) fractions of normal turbot serum, but phagocytosis of Glugea caulleryi or Tetramicra brevifilum spores was not affected by either fraction. Neither anti-G. caulleryi immune serum, nor anti-T. brevifilum immune serum (which cross-reacted considerably with G. caulleryi antigens), enhanced phagocytosis of G. caulleryi spores. Finally, spores treated with sodium m-periodate (to modify the structure of surface-borne sugars) were less effectively ingested than untreated spores, suggesting that phagocytosis of microsporidian spores involves recognition of such sugars by the phagocytic cell. The results of this study support the hypothesis that microsporidian parasites of fish in some way modulate the host phagocytic responses.

Opportunistic intestinal protozoa in chronic diarrhoeic immunosuppressed patients

Chronic diarrhoea accompanied by weight loss is a common and often debilitating problem in immunocompromized patients, receiving chemotherapeutic agents. In these patients, the intestinal opportunistic parasites probably played a major role in causing this clinical manifestation. The present work, aims to search for these parasites. Special stains for each parasite were used to differentiate it easily from the fecal elements, obviating the need for diagnostic invasive techniques especially used in microsporidial infection. The detected parasites were, Giardia lamblia (17.7%) best seen by iron haematoxylin stain. Coccidian oocysts (Cryptosporidia; 13.3% Isospora belli; 2.2%) were clearly seen by using Ziehl-Neelsen and Chromotrope-based stains. The Gram positive spores of Enterocytozoon bieneusi were (4.4%) and best seen by using chromotrope-based stain, where as Giemsa failed in their diagnosis.

Serologic responses of cattle and other animals infected with Neospora caninum

OBJECTIVE

To examine cross-reactivity among Neospora caninum and closely-related apicomplexans.

DESIGN

Sera from animals were examined for antibody production to N caninum and cross-reactivity to Toxoplasma gondii.

ANIMALS

Cattle were experimentally infected with 3 tissue cyst-forming protozoan parasites N caninum, T gondii, and Sarcocystis sp, and calves were monospecifically inoculated with the intestinal coccidia, Eimeria bovis and Cryptosporidium parvum. Similar studies were done in laboratory rabbits inoculated with N caninum, T gondii, Hammondia hammondi, and Sarcocystis sp. Additionally, sera were obtained from ewes, lambs, goats, sows, cats, rats, and mice inoculated with N caninum tachyzoites.

PROCEDURE

The indirect fluorescent antibody (IFA) and ELISA antibody tests (cattle only) were used to examine reactivity to N caninum; the modified direct agglutination, Sabin-Feldman dye, and IFA tests were used to evaluate reactivity to T gondii.

RESULTS

Serologic cross-reactivity among N caninum, T gondii, and Sarcocystis sp was none or minimal by the IFA test. There was some reactivity to N caninum by the use of ELISA in cattle inoculated with Sarcocystis sp.

CONCLUSIONS

The IFA test for N caninum was specific for the diagnosis of neosporosis in animals.

Interleukin-12 an integral cytokine in the immune response

Interleukin 12 (IL-12) is a heterodimeric cytokine that is produced primarily by antigen-presenting cells and plays a primary role in the induction of cell-mediated immunity. This function is promoted by the IL-12 induced production of interferon-gamma (IFN-gamma) from both resting and activated NK and T cells, by the proliferative activity of IL-12 on activated NK and T cells, by enhancing the cytotoxic activity of NK cells, and by supporting cytotoxic T lymphocyte generation. IL-12 and IL-12-induced IFN-gamma promote the development of naive T cells into Th1 cells and the proliferation and IFN-gamma secretion by differentiated Th1 cells in response to antigen. IL-12 has been found to exhibit many of these activities in vivo, as well as in vitro, and thus IL-12 plays an important role in both innate resistance and antigen-specific adaptive immunity to intracellular bacterial, fungal, and protozoan pathogens. Due to its effects on T cells, recombinant IL-12 has been shown to have therapeutic activity in a variety of mouse tumor and infectious disease models and is being evaluated in clinical trials in human cancer patients. IL-12 also appears to play a role in the genesis of some forms of immunopathology, including endotoxin-induced shock and some autoimmune diseases associated with aberrant Th1 activity. Therefore, IL-12 antagonists may also have therapeutic potential in the treatment of auto immune disorders.

M cells and the pathogenesis of mucosal and systemic infections

M cells are specialized epithelial cells of mucosal surfaces lining the respiratory and intestinal tracts. They participate in generating mucosal immune protection by sampling and delivering antigens to the underlying lymphoid tissue. A variety of viral, bacterial and protozoal pathogens exploit the M cell transport pathway to breach mucosal barriers and establish local or systemic infections.

Efficacy of a live Cryptobia salmositica vaccine, and the mechanism of protection in vaccinated rainbow trout, Oncorhynchus mykiss, against cryptobiosis

An attenuated strain of Cryptobia salmositica was used as a live vaccine to protect rainbow trout, Oncorhynchus mykiss, against cryptobiosis. Fish immunized with 1.0 x 10(4) or 5.5 x 10(4) attenuated C. salmositica per fish were protected 3 weeks after immunization; however, this period was reduced to 2 weeks if fish were vaccinated with 1.0 x 10(5) attenuated parasites per fish. Fish were still protected at 6, 12 and 24 months after vaccination. Complement fixing antibodies in the blood of immunized fish lysed C. salmositica under in vitro conditions. The titre of complement fixing antibodies in vaccinated fish increased rapidly 1-2 weeks post-challenge. In vitro phagocytosis was enhanced by antiserum and by activated macrophages from vaccinated fish. There was also evidence of antibody independent and antibody dependent cell-mediated cytotoxicity in vaccinated fish.

Peptides as weapons against microorganisms in the chemical defense system of vertebrates

The innate immunity of vertebrates to microbial invasion is arbitrated by a network of host-defense mechanisms involving both the long-lasting highly specific responses of the cell-mediated immune system and a nonspecific chemical defense system based on a series of broad-spectrum antimicrobial peptides that are analogous to those found in insects. Vertebrate antibiotic peptides secreted by nonlymphoid cells of the mucosal surfaces of the respiratory and gastrointestinal tracts as well as by the granular glands of the skin reportedly cause the lysis of numerous pathogenic microorganisms, including viruses, gram-positive and gram-negative bacteria, protozoa, yeasts, and fungi, as well as of cancer cells. Antimicrobial peptides isolated from vertebrates have three characteristic properties: They are relatively small (20-46 amino acid residues), basic (lysine- or arginine-rich), and amphipathic. Although these peptides differ widely in length and amino acid sequences, they may be grouped in four broad families based on characteristic structural features. Although the precise mechanism of action of these peptides remains to be defined, their microbicidal effect very likely results from their capacity to form channels or pores within the microbial membrane in order to permeate the cell and impair its ability to carry out anabolic processes. This secondary, chemical immune system provides vertebrates with a repertoire of small peptides that are promptly synthesized upon induction, easily stored in large amounts, and readily available for antimicrobial warfare.

Investigations into the ubiquitous nature of high or low immune responsiveness after divergent selection for antibody production in common carp (Cyprinus carpio L.)

This paper reports on the selection of individual carp with a high or low antibody response, in combination with reproduction by gynogenesis, in order to develop well-characterised inbred carp lines consisting of practically unlimited numbers of carp with the same genotype. Two homozygous progenies, previously characterised as having a high or low immune response to dinitrophenyl keyhole limpet haemocyanin (DNP-KLH), were immunised with either a T-dependent (DNP-human serum albumin (DNP-HSA)) or T-independent (trinitrophenyl lipopolysaccharide (TNP-LPS)) hapten-carrier complex. In comparison with the antibody response after DNP-KLH immunisation, the response to DNP-HSA was observed to be highly variable and did not differ between the divergently selected progenies. This suggests that the divergent selection for antibody production to DNP-KLH has been carrier-specific. Immunisation with T-independent TNP-LPS induced a very rapid response which differed between the high and low responders, and likely measured changes in the DNP-specific precursor pool of B cells caused by the selection. A number of selected individuals with a high immune response to DNP-KLH were infected with Trypanoplasma borreli, a haemoflagellate parasite of carp, to examine a possible relationship between the increase in immune responsiveness and disease resistance, but no change could be detected. However, individual homozygous carp were able to escape inbreeding depression and survive the infection. Such carp would be likely candidates for gynogenetic reproduction to obtain viable inbred carp lines.

Use of an animal model of trichomoniasis as a basis for understanding this disease in women

Studies of host-parasite relationships in bovine trichomoniasis are presented as a basis for understanding mechanisms of pathogenesis and protection in trichomoniasis in women. The bovine infection is caused by Trichomonas foetus, a trichomonad species closely related to the human pathogen Trichomonas vaginalis. An estrogenized murine model infected with T. vaginalis is useful for the study of virulence factors, but the bovine model has advantages for the study of immunity because T. foetus infection is common in this natural host. In vitro, several virulence factors similar to those of T. vaginalis have been studied, including cysteine proteinases, binding of host cell proteins, and factors involved in attachment to vaginal cells. The biggest advantage of the bovine model, however, is that an efficacious systemic vaccination has been demonstrated to both prevent and treat T. foetus infection. The specificity and isotype of antibodies involved in protection have also been defined. These findings provide encouragement for the development of vaccines against trichomoniasis in humans.

Genetic variation in susceptibility to Trypanoplasma borreli infection in common carp (Cyprinus carpio L.)

Gynogenetic reproduction of homozygous females, or crossbreeding two homozygous animals, results in fish lines without genetic variation. Hybrid crosses are expected to express a more stable development than homozygous lines, the latter may have an important value for gaining insight into genetic components of host resistance to parasite infection. We examined the antibody response of carp (Cyprinus carpio L.) to infection with Trypanoplasma borreli. Outbred carp responded with a production of specific antibodies, but highly susceptible isogenic hybrid carp did not. This suggests an apparent relationship between susceptibility and the lack of specific antibody production. This relation was partially confirmed by the passive transfer of immunity with immune plasma. In addition, two isogenic homozygous carp lines were highly susceptible to the trypanoplasm (100% mortality), in contrast with outbred carp, the majority of which survived infection. None of the carp in either homozygous carp line produced an antibody response to parasite-unrelated antigen (DNP-KLH). This suggests that the low antibody response was not entirely due to a poor state of health, but that these carp have a genetically predetermined low antibody response.

Bovine vaginal antibody responses to immunoaffinity-purified surface antigen of Tritrichomonas foetus

Bovine trichomoniasis is a prevalent sexually transmitted disease of cattle caused by the protozoan Tritrichomonas foetus. Currently, diagnosis is most often made by culture. In order to provide a faster immunodiagnostic approach, a specific enzyme-linked immunosorbent assay (ELISA) was investigated. A protective surface antigen (TF1.17 antigen) of T. foetus was immunoaffinity purified and used in an ELISA to detect antibodies in vaginal mucus from heifers inoculated with T. foetus. In preliminary studies, antibodies of the immunoglobulin A (IgA) isotype were detected in mucus from all experimentally infected heifers which were tested at 6 weeks postinoculation, whereas IgG1 and IgG2 were not. In addition, IgA responses detected in postinoculation samples were all greater than those detected in preinoculation samples, unlike those detected by a whole-cell antigen ELISA. For these two reasons, IgA antibodies appeared to be useful diagnostically. Further investigation of IgA antibodies used vaginal mucus collected weekly from heifers inoculated intravaginally with 10(2), 10(4), or 10(6) T. foetus organisms. Heifers with positive cultures for T. foetus had similar IgA responses to TF1.17 antigen over the 10 weeks of infection regardless of the initial inoculum dose. This indicates that if the dose is sufficient to establish infection, the magnitude and duration of the immune response are no longer dependent on dose. All of the infected animals receiving all dosages responded with high absorbance values in the IgA anti-TF1.17 antigen ELISA by 6 weeks postinoculation, and all absorbance values remained high at 10 weeks. To determine the duration of the IgA response, four other heifers inoculated with 7 x 10(6) T. foetus organisms were studied through 24 weeks postinoculation. IgA antibody responses to TF1.17 antigen were still high at 24 weeks, even though some heifers cleared the infection several weeks earlier. These results indicate that experimentally infected heifers produced detectable long-lasting IgA responses to TF1.17 antigen in vaginal mucus, which may be useful in a herd test for the diagnosis of bovine trichomoniasis.

Specific antibodies in serum and vaginal mucus of heifers inoculated with a vaccine containing Tritrichomonas foetus

Thirty-five heifers were allotted to 3 groups. Group 1 (control) consisted of 10 heifers that were not vaccinated and were challenge exposed by breeding to infected bulls. Group 2 (natural challenge exposure) consisted of 10 heifers that were vaccinated and challenge exposed by breeding to infected bulls. Group 3 (experimental challenge exposure) consisted of 15 heifers that were vaccinated and challenge exposed by breeding to infected bulls and by intravaginal inoculation with 10(7) Tritrichomonas foetus. Total immunoglobulin concentrations and specific trichomonal antibodies were determined in serum and vaginal secretions of heifers, using radial immunodiffusion and ELISA procedures. Control heifers remained infected for a mean of 10.6 weeks (range, 0 to 18 weeks), and heifers of the natural and experimental challenge-exposure groups remained infected for 3.2 and 5.0 weeks, respectively (range, 0 to 12 weeks). Total serum and cervicovaginal mucus concentrations of IgM, IgA, IgG1, and IgG2 did not change significantly after vaccination or challenge exposure. However, ELISA titers of total trichomonal antibodies increased up to 1:10,000 (range, 1:400 to 1:10,000) in serum after vaccination, and increased approximately tenfold above background in cervicovaginal mucus. In serum, the predominant trichomonal antibody isotype was IgG1, although trichomonal IgA and IgM antibodies also increased. The predominant trichomonal antibody detected in cervicovaginal mucus was IgA. Antibody titers in serum and cervicovaginal mucus of vaccinated heifers were not increased by infection. However, in control heifers, the total local trichomonal antibody response increased three- to fivefold after infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides as weapons against microorganisms in the chemical defense system of vertebrates

The innate immunity of vertebrates to microbial invasion is arbitrated by a network of host-defense mechanisms involving both the long-lasting highly specific responses of the cell-mediated immune system and a nonspecific chemical defense system based on a series of broad-spectrum antimicrobial peptides that are analogous to those found in insects. Vertebrate antibiotic peptides secreted by nonlymphoid cells of the mucosal surfaces of the respiratory and gastrointestinal tracts as well as by the granular glands of the skin reportedly cause the lysis of numerous pathogenic microorganisms, including viruses, gram-positive and gram-negative bacteria, protozoa, yeasts, and fungi, as well as of cancer cells. Antimicrobial peptides isolated from vertebrates have three characteristic properties: They are relatively small (20-46 amino acid residues), basic (lysine- or arginine-rich), and amphipathic. Although these peptides differ widely in length and amino acid sequences, they may be grouped in four broad families based on characteristic structural features. Although the precise mechanism of action of these peptides remains to be defined, their microbicidal effect very likely results from their capacity to form channels or pores within the microbial membrane in order to permeate the cell and impair its ability to carry out anabolic processes. This secondary, chemical immune system provides vertebrates with a repertoire of small peptides that are promptly synthesized upon induction, easily stored in large amounts, and readily available for antimicrobial warfare.

Soluble IL-4 receptor, potential for therapeutic and prophylactic intervention

Many bacterial, protozoal and viral infections trigger a cell-mediated immune response. Of special importance for the clinical outcome of disease, however, is the relative predominance of T helper (Th) cell populations (Th1 and Th2) secreting different patterns of lymphokines. Preferential development of one Th subset occurs apparent at the early stages of an infection, suggesting that the mechanisms driving the immune response in one direction or the other operate soon after exposure to the antigen. Cytokines are among the most important factors regulating T cell differentiation and expansion of the different T cell subtypes. As in experimental candidiasis, listeriosis, yersiniosis and murine retrovirus induced immunodeficiency syndrome (MAIDS), interleukin-4 (IL-4) is of central importance also for the clinical course of murine cutaneous leishmaniasis. It has been demonstrated that the presence of IL-4 is essential for the development of disease promoting Th2 cells whereas neutralization of IL-4 in vivo led to establishment of protective immunity against leishmania. A naturally occurring antagonist of IL-4 is the soluble IL-4 receptor (sIL-4R), which retains its ligand binding properties and binds IL-4 with high affinity. We therefore examined the immunomodulatory and therapeutic capacity of recombinant sIL-4R in murine cutaneous leishmaniasis. BALB/c mice were treated with recombinant sIL-4+ during the onset of the immune response. This treatment rendered BALB/c mice clinically resistant to Leishmania major (L. major), led to reduced parasite load, shifted the pattern of cytokines towards Th1 type and provided durable resistance against reinfection with L. major.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastrointestinal disease in the immunocompromised patient

Gastrointestinal (GI) disease is frequent in all types of immunocompromised patients but occurs with greatest frequency in patients with acquired immunodeficiency syndrome (AIDS). Thus, much of this review deals with human immunodeficiency virus (HIV)-related GI diseases. Gastrointestinal diseases in other immunocompromised patients are compared with those in patients with AIDS. Conditions unique to transplant recipients, such as graft-versus-host disease (GVHD) and posttransplant lymphoproliferative disorders (PTLDs), are discussed separately. We have divided these GI diseases into four main categories: (1) HIV-related inflammatory conditions other than opportunistic infections (HIV-related enteropathy, proctocolitis, and CD8 lymphocytosis); (2) inflammatory conditions unrelated to HIV or opportunistic infections (neutropenic enterocolitis, regional enteritislike enteropathy, and GVHD); (3) opportunistic infections (illnesses caused by herpesvirus, cytomegalovirus, and miscellaneous other viruses; Mycobacterium, Candida, Histoplasma, Cryptococcus, Cryptosporidium, Microsporida, Isospora, Leishmania, Toxoplasma and Strongyloides organisms as well as Pneumocystitis carinii; and (4) neoplasias (Kaposi's sarcoma [KS], AIDS-related non-Hodgkin's lymphoma [NHL], HIV-related Hodgkin's disease [HD], PTLDs, and miscellaneous neoplasms). The prevalence, pathogenesis, clinical manifestations, gross pathological findings, and microscopic features of each disease entity are discussed.

A review on vaccination against protozoa and arthropods of veterinary importance

The recent advances in immunology and biotechnology have stimulated much research on the control of parasitic diseases through vaccination. This is a review of the state of the art regarding important protozoan and arthropod veterinary parasites. A live oocyst vaccine for avian coccidiosis is still in use but much work has been done on the identification, cloning, and assay of protective antigens. The sporozoites of Eimeria tenella have been the preferred subject and at least four recombinant antigens have already been tested with partial success. Premunization against babesiosis is still widely used in Latin America as is a live vaccine with attenuated parasites in Australia. At least three Babesia bovis and three Babesia bigemina antigens that generate partial protection have been produced as recombinant proteins. A vaccine against canine babesiosis is being commercialized in France. Infection-treatment is still used to vaccinate against Theileria parva and a schizont vaccine against Theileria annulata. Recombinant sporozoite antigens have been assayed with partial success against both species but the identification and administration of protective schizont antigens, regarded as the most important, still requires considerable work. The immunological control of African trypanosomoses is still impaired by the antigenic variation that the parasites experience during the infection. Although some possibilities exist, most specialists are pessimistic about the promise of developing a vaccine in the near future. Control of Boophilus ticks with an occult tick intestine recombinant antigen seems to have potential in inhibiting reproduction of the tick but salivary antigens appear to be more effective at inhibiting feeding and pathogen transmission. Vaccination with a Hypoderma protein, recently cloned, has induced 90% protection against subsequent infestations. It is very likely that effective vaccines against veterinary parasites will become available in the near future.

[The role of opportunistic protozoa in human pathology today]

The paper deals with opportunistic protozoa, their common properties distinctions from commensals and obligate parasites, and the specific features of their caused opportunistic infections. It also provides evidence for the increasing contribution of opportunistic protozoa to human pathology today and for paramount necessity for researchers and practitioners of various disciplines to lay a special emphasis on them.

[Immune response to antibiotics in patients with secondary immunodeficiencies]

A biological response modifier (BRM) has been defined as an agent able to modulate effector mechanisms or mediators of host defence. Some antibiotic molecules have been shown to display a BRM like activity, being able to enhance immune responses (certain cephalosporins), to synergize with the immune effectors (macrolides, quinolones) or alternatively, to depress immune functions (tetracyclines or antimycotic drugs). The BRM-like activity of different antibiotic molecules has been widely reported in in vitro studies as well as ex vivo in experimental animal models. Only recently some Authors have approached the problem by investigating whether the in vivo administration of antibiotic was able to affect different immune effector functions, either in healthy subjects or in patients. The main question in the field is the possible clinical impact of the connections between antibiotics and the immune system, particularly in subjects with acquired immunodeficiency in whom the impairment of the immune responses leads to increased susceptibility to infectious processes. Ex vivo data seem to suggest that cefodizime, one of the newest third-generation cephalosporins, is able to enhance phagocyte and mononuclear cell functions in healthy volunteers, thus confirming the possibility of combining an antibacterial efficacy with the ability to restore or enhance immune responses. Comparable data in studies investigating the effect of cefodizime on immune functions in immunocompromised patients such as elderly subjects, hemodialyzed or diabetic patients, BPCO subjects, patients undergoing surgical stress and patients with multiple myeloma are more important from a practical clinical point of view.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial and protozoal infections in genetically disrupted mice

Immune gene knock-out mice have provided challenging new opportunities for scientists interested in infection and immunity. This novel experimental approach has made it possible to gain deeper insights into the mechanisms that are operative in defence against, and the pathology of, infectious disease. It has allowed the identification not only of vital immune elements, but also of compensatory mechanisms and of novel cells that are still uncharacterized or of uncertain function.

Application of knockout mice to the experimental analysis of infections with bacteria and protozoa

Knockout mice with distinct gene deletions are valuable tools for in vivo analyses of the immune response against infectious agents. Studies of bacterial and protozoal infections have shown that antimicrobial immunity is generally defective in knockout mice. At one extreme, deletion of just one gene may completely compromise resistance, while at the other extreme, redundancy in the immune system allows partial compensation for the deleted part.

Interleukin-12: a bridge between innate resistance and adaptive immunity with a role in infection and acquired immunodeficiency

Interleukin-12 (IL-12) is a disulfide-linked heterodimeric cytokine originally identified as a product of EBV-transformed B cell lines. Monocyte/macrophages are the physiologically most relevant producers of IL-12, in response to both Gram-positive and -negative bacteria, bacterial products, and intracellular parasites. Although IL-12 has an enhancing effect on the survival and growth of early hematopoietic progenitor cells, most of the IL-12 biological activity has been described on T and NK cells, on which it induces production of lymphokines, primarily IFN-gamma, enhances cytotoxic activity, and, in cooperation with other stimuli, increases proliferation. IL-12 is an inducer of development of T helper type 1 (Th-1) cells and the equilibrium between IL-12 and IL-4 is probably important for the balance in vivo between Th-1 and Th-2 responses. IL-12 has an important role in the host resistance to infection, in particular to intracellular pathogens, by activating macrophages through induction of IFN-gamma from NK and T cells and by enhancing cell-mediated immune responses, dependent on Th-1 cell development. Peripheral blood mononuclear cells from HIV-seropositive individuals are impaired in their ability to produce IL-12 in response to bacterial stimulation, and IL-12 restores in vitro some of the depressed immunological functions, suggesting that a defect in IL-12 production may have a pathogenic role in the immunodeficiency of HIV-infected individuals. Natural IL-12 appears to provide a regulatory link between innate resistance and the development of the antigen-specific adaptive immune response and the recombinant protein has therapeutic potential because of its activity against tumors and infections and its effectiveness as an adjuvant enhancing cell-mediated immunity in vaccination.

Detection of antibodies in sera from Chagas' disease patients using a Trypanosoma cruzi immunodominant recombinant antigen

A Trypanosoma cruzi DNA fragment encoding an immunodominant repetitive antigen (H49) was subcloned into a protein purification and expressed system. Purified H49 peptide reacted specifically in an enzyme-linked immunosorbent assay (ELISA) with sera from T. cruzi-infected patients, but not with sera from patients with other parasitic diseases such as leishmaniasis and T. rangeli-infection. The H49 recombinant ELISA was able to detect specific antibodies in 84% of chronic chagasic serum samples tested. One of the major advantage of the recombinant ELISA for serodiagnosis of chronic Chagas' disease resides in its high specificity (100%). Our data suggest that recombinant peptides could provide a practical basis for specific diagnosis tests for Chagas' disease.

IgM and IgA rheumatoid factors in canine polyarthritis

IgM and IgA rheumatoid factor (RF) were detected by ELISA using a purified dog IgG as antigen in normal controls (N = 84), dogs with unclassified polyarthritis (N = 95), dogs with rheumatoid arthritis (RA) (N = 22), dogs with systemic lupus erythematosus (SLE) (N = 35), dogs with leishmaniasis or heart worm disease (N = 20) and dogs with pyometra (N = 16). Frequency and titre of IgM and IgA RF are low and comparable (P < 0.05) in dogs with unclassified polyarthritis or RA: respectively 24.2% and 27.3% for IgM RF and 21.0% and 18.2% for IgA RF; the mean titre being respectively 0.781 +/- 0.581 and 0.649 +/- 0.365 for IgM RF, and 0.774 +/- 1.331 and 0.740 +/- 1.169 for IgA RF. The frequencies of IgM and IgA RF are a little higher in dogs with SLE (IgM RF: 37.1%, IgA RF: 25.7%) and higher in dogs with leishmaniasis or heart worm disease (45.0% and 30.0%), especially in dogs with pyometra (68.7% and 37.5%). So, although dogs can produce IgM and IgA RF, these auto-antibodies are uncommon in dogs with RA. Furthermore, when RF are present their titre is much lower than in human RA.

Conservation of a protective surface antigen of Tritrichomonas foetus

Bovine trichomoniasis is a sexually transmitted disease caused by the flagellated protozoan Tritrichomonas foetus. A protective surface antigen was previously identified and immunoaffinity purified from T. foetus isolate D1 with cross-reactive monoclonal antibodies (MAbs) TF1.15 and TF1.17 (BonDurant, R. H., R. R. Corbeil, and L. B. Corbeil, Infect. Immun. 61:1385-1394, 1993). This antigen elicited antibody responses in the serum and cervicovaginal mucus of heifers. Thus, it may be useful as an immunodiagnostic reagent as well as a subunit vaccine. Conservation of the antigen in all strains would be crucial for either application. We investigated the conservation of this antigen among 36 isolates of T. foetus from Argentina, Costa Rica, and the United States using MAbs TF1.15 and TF1.17 in an enzyme-linked immunosorbent assay. MAb TF1.17 reacted with 32 of the 36 isolates, whereas MAb TF1.15 reacted with all of the isolates tested. One of the isolates which did not react with MAb TF1.17 (i.e., D1#3) was investigated further by Western blotting (immunoblotting) to determine the reason for the lack of reactivity with one of the two cross-reactive MAbs. The antigenic band that was reactive with MAb TF1.15 had a molecular mass slightly lower than that of the corresponding band from isolate D1, which reacted with both MAbs TF1.15 and TF1.17. Thus, at least a major portion of the antigen appeared to be conserved. This was confirmed in a study of heifers infected with isolate D1#3. The vaginal immunoglobulin A antibodies of these infected heifers reacted with the antigen of isolate D1 that was immunoaffinity purified with MAb TF1.17. Therefore, even though the epitope recognized by MAb TF1.17 was missing in the challenge isolate (D1#3), the heifers developed an immune response to the rest of the molecule. These results indicate that the major portion of the previously described protective antigen is conserved in different isolates of T. foetus. This portion contains the epitope that reacts with MAb TF1.15. Most isolates express the whole antigen, which possesses both TFl.15 and TF1.17 epitopes, but the few isolates that are missing the portion containing the TF1.17 epitope may still elicit an immune reponse to the conserved portion. Thus, the protective surface antigen is promising for use in immunodiagnosis or vaccination against bovine trichomoniasis.

The role of natural killer cells in innate resistance to infection

Natural killer cells were first identified by their cytotoxic activity against tumor cells, suggesting a role in immunological surveillance against neoplasia. However, there is now increasing evidence that natural killer cells are important mediators of innate resistance against a variety of pathogenic micro-organisms. Recently, several important advances have been made in our understanding of how these cells are activated during infection, the contribution of cytokines derived from natural killer cells to host resistance and their influence on the development of antigen-specific T-cell responses.

Elevated levels of antibodies against sulphatide are present in all chronic chagasic and dilated cardiomyopathy sera

A natural anti-sulphatide antibody was found to be present in the serum of every normal individual studied. The reactivity of the antibody was assessed by its interaction with galactosylceramide-I3-sulphate. Antigen-antibody binding was strongly blocked by 1 mM heparin, dextran sulphate and chondroitin sulphate A, and by 5 mM chondroitin sulphate B. Antibodies avidly absorb to rabbit erythrocytes, but discretely to rat erythrocytes, suggesting that they are different from galactocerebroside antibodies. Elevated levels of sulphatide antibodies were present in all of 102 chronic Trypanosoma cruzi-infected patients studied, but not in other patients having cutaneous or visceral leishmaniasis, T. rangeli infection or several other protozoal, helminthic or mycotic infections. Interestingly, 100% of 40 dilated cardiomyopathy patients also have elevated levels of sulphatide antibodies. As T. cruzi is rich in galactocerebroside sulphate, it is proposed that in chagasic patients this glycolipid could act as an immunogen, inducing elevated titres of sulphatide antibodies, which could be important in the pathogenesis of cardiac or peripheral nerve symptoms.

Effects of inoculum route and dose on the immune response of common carp, Cyprinus carpio to the blood parasite, Trypanoplasma borreli

Carp were inoculated intramuscularly (im) or intraperitoneally (ip) with different doses of live Trypanoplasma borreli. Prepatent period was shortened by using the im route and by increasing the dose. Haematocrit was reduced following im inoculation with 9.5 x 10(5) parasites. Most fish recovered between 8 and 13 weeks post-inoculation (wpi). Neither parasitaemia nor anaemia was detected in any recovered fish following homologous challenge. An enzyme-linked immunosorbent assay was developed to quantitate antibody response elicited by the parasite. Antibody levels rose rapidly during the first 4 wpi. The response elicited by increased dose was significantly higher only at 4 wpi. Route of exposure did not affect antibody response. Peak responses coincided with decline and eventual absence of parasitaemia.

In vitro isolation and characterization of a Neospora sp. from aborted bovine foetuses

A Neospora sp. was isolated from the brains of two aborted bovine foetuses and grown continuously in vitro in bovine cell cultures. A comparison of the antigenic reactivity of in vitro cultivated tachyzoites with polyclonal antisera to Neospora caninum, Hammondia hammondi or Toxoplasma gondii revealed that the bovine protozoal isolates were similar to N. caninum and antigenically distinct from T. gondii. Tachyzoites of both bovine isolates had similar ultrastructural features, including an apical polar ring, conoid, electron-dense rhoptries and micronemes. The orientation of the micronemes, presence of micropores and a large number of electron-dense granules in the posterior portion of the bovine isolate tachyzoites differed from previous descriptions of N. caninum in vivo. Tachyzoites of the bovine isolates were ultrastructurally more similar to in vitro cultivated N. caninum tachyzoites than to tachyzoites of T. gondii or H. hammondi. The antigenic and ultrastructural similarities between N. caninum and the protozoal parasites isolated from aborted bovine foetuses in this study support the proposition that these parasites belong to the genus Neospora.

Prevalence of antibodies to Neospora caninum in a population of urban dogs in England

Of 163 dogs, randomly selected from those examined at the University of Liverpool Small Animal Hospital, 12.9 per cent had antibody titres > or = to 1/200 to Neospora caninum in an indirect fluorescent antibody test. None was apparently suffering clinical neosporosis. There was no association between the occurrence of neospora antibodies and either toxoplasma antibodies measured by the dye test, sex, age, type of feeding or the presence of other dogs in the household. Antibody was detected at titres > or = to 1/200 in nine breeds, suggesting that there is a substantial level of subclinical infection in British dogs.

Congenital Neospora infection in calves born from cows that had previously aborted Neospora-infected fetuses: four cases (1990-1992)

Four dairy cows that had been successfully rebred following fetal Neospora infection and abortion were identified from 2 drylot dairies. All 4 cows had uncomplicated pregnancies with the birth of 5 full-term calves. The calves all had high precolostral serum IgG antibodies. The precolostral antibodies to Neospora sp as determined by indirect fluorescent antibody test ranged from 5,120 to 20,480, compared with maternal serum and colostral antibody titers from 320 to 1,280. Two calves had mild neurologic limb deficits. Three calves had mild nonsuppurative encephalomyelitis and Neospora organisms were found in the CNS of 3 calves. Findings indicate that repeat transplacental Neospora infections occur in cows. Additionally, calves born from cows with a history of Neospora fetal infection and abortion may have congenital Neospora infections and/or neurologic dysfunctions at birth. The Neospora indirect fluorescent antibody test appears to be a useful antemortem test for detection of calves exposed in utero to Neospora organisms.

Pathologic effects of Sphaerospora dicentrarchi Sitjà-Bobadilla and Alvarez-Pellitero, 1992 and S. testicularis Sitjà-Bobadilla and Alvarez-Pellitero, 1990 (Myxosporea: Bivalvulida) parasitic in the Mediterranean sea bass Dicentrarchus labrax L. (Teleostei: Serranidae) and the cell-mediated immune reaction: a light and electron microscopy study

In the present study, the pathogenic effects of Sphaerospora dicentrarchi and S. testicularis, histozoic and coelozoic myxosporean parasites of the Mediterranean sea bass Dicentrarchus labrax L., respectively, are described. The infection caused by the latter, which usually invades the testes and neighboring tissues, is considered to represent parasitic castration. S. dicentrarchi seems to be harmless except in massive infections, which probably result in organic disfunctions. The cellular host reaction generated by S. testicularis depends on the location of the parasite and is more intense than that produced by S. dicentrarchi. In both sphaerosporoses, macrophages, granulocytes, lymphocytes, plasmacytes, and fibroblast-like cells are involved. The role of the different immune cells is discussed.