Differential resource allocation in deer mice exposed to sin nombre virus

The resource allocation hypothesis predicts that reproductive activity suppresses immunocompetence; however, this has never been tested in an endemic disease system with free-ranging mammals. We tested the resource allocation hypothesis in wild deer mice (Peromyscus maniculatus) with natural exposure to Sin Nombre Virus (SNV). Immunocompetence was estimated from the extent of swelling elicited after deer mice were injected with phytohemagglutinin (PHA); swelling is positively correlated with immunocompetence. After livetrapping deer mice, we determined their reproductive state and SNV infection status. Males were more likely to be seropositive for SNV than females (37% vs. 25%) and exhibited 10% less swelling after PHA injection. The swelling response of females differed with both infection status and reproductive condition. There was also a significant infection status by reproductive condition interaction: non-reproductive, seropositive females experienced the least amount of swelling, whereas females in all other categories experienced significantly greater swelling. The swelling response of males differed with both SNV infection status and reproductive condition, but there was no significant infection status by reproductive condition interaction. Seronegative males elicited greater swelling than seropositive males regardless of reproductive status. In contrast to the resource allocation hypothesis, these results do not indicate that reproductive activity suppresses immunocompetence of deer mice but rather suggest that chronic SNV infection reduces immunocompetence. Sex-based differences in swelling indicate that SNV modulates the immune system of female deer mice differently than it does that of males, particularly during reproduction. We propose that differences in resource allocation between males and females could result from inherent sex-based differences in parental investment.     

Changes in sin nombre virus antibody prevalence in deer mice across seasons: the interaction between habitat, sex, and infection in deer mice

We examined the impact of season and habitat on Sin Nombre virus (SNV) seroprevalence in deer mice (Peromyscus maniculatus) in Utah's Great Basin Desert from May 2002 through summer 2003. Low mouse captures in 2002 limited analysis for that year. In two seasons during 2003, mouse density and sagebrush cover were positively linked (spring: r = 0.8, P = 0.01; summer: r = 0.8, P = 0.04). In the spring, seroprevalence was negatively correlated with density (r = -0.9, P< 0.01); male and female antibody prevalence did not differ; and scarring was unrelated to antibody status. In the summer, density and antibody prevalence were unrelated; male seroprevalence was higher (chi(2) = 3.6, P = 0.05); and seropositive mice had more scars (t = 2.5, P = 0.02). We speculate nesting behavior could maintain SNV over the winter, whereas summer territoriality could be responsible for transmission.     

Role of intraepithelial lymphocytes in mucosal immune responses of mice experimentally infected with Cryptosporidium parvum

In order to investigate the role of intestinal intraepithelial lymphocytes (IELs) in host defense against Cryptosporidium parvum infection, conventionally bred immunocompetent (ImCT) ICR mice and immunosuppressed (ImSP) littermates were infected orally with 10(6) C. parvum oocysts. Then fecal oocyst excretion, the number and location of IELs, and their T lymphocyte subsets were observed on days 4, 7, 10, 13, 16, and 20 postinfection (PI). Uninfected ImCT and ImSP mice were used as controls. The starting point of oocyst excretion was day 4 PI in both ImCT- and ImSP-infected mice. The highest oocyst excretion occurred on day 7 PI in both groups, though the number of oocysts excreted was 3 times greater in ImSP than in ImCT mice. In ImCT mice, IELs greatly increased in number on days 16 and 20 PI (P < 0.05), but the increase was minimal in ImSP mice. IELs changed their location from the basal area to intermediate and apical areas of villous epithelial cells during the early stage of infection. In ImCT-infected mice, IEL phenotypes also changed; whereas CD4+ cells increased temporarily on day 7 PI (P < 0.05), CD8+ cells increased significantly on days 16 and 20 PI (P < 0.05). The results strongly suggest that IELs play a significant role in host defense against C. parvum infection, with helper T cells initiating control of the infection and cytotoxic T cells eliminating the parasites.     

Encephalomyelitis in mice experimentally infected with Akabane virus.

Lesions in the central nervous system of mice, induced by intracerebral injection of Akabane virus, were observed by the fluorescent antibody technique and histological method. Fluorescent antigens were recognized in the cytoplasm of nerve cells, but were not detected exactly in any other part. Fluoresced nerve cells were distributed almost all over the central nervous system, especially in medulla oblongata and spinal cord. The appearance of fluorescent antigens was followed by histological changes. So-called Nissl's acute severe degeneration was observed in nerve cells in the area where the fluorescent antigens were distributed. Spongy foci were seen in medulla oblongata and spinal cord. Virus was recovered from brain and spinal cord, but not from any other visceral organ or blood. Akabane virus showed an affinity to nerve cells and caused primary nonpurulent encephalomyelitis when inoculated intracerebrally to mice.     

Horses experimentally infected with Sarcocystis neurona develop altered immune responses in vitro

Equine protozoal myeloencephalitis (EPM) due to Sarcocystis neurona infection is 1 of the most common neurologic diseases in horses in the United States. The mechanisms by which most horses resist disease, as well as the possible mechanisms by which the immune system may be suppressed in horses that develop EPM, are not known. Therefore, the objectives of this study were to determine whether horses experimentally infected with S. neurona developed suppressed immune responses. Thirteen horses that were negative for S. neurona antibodies in serum and cerebrospinal fluid (CSF) were randomly assigned to control (n = 5) or infected (n = 8) treatment groups. Neurologic exams and cerebrospinal fluid analyses were performed prior to, and following, S. neurona infection. Prior to, and at multiple time points following infection, immune parameters were determined. All 8 S. neurona-infected horses developed clinical signs consistent with EPM, and had S. neurona antibodies in the serum and CSF. Both infected and control horses had increased percentages (P < 0.05) of B cells at 28 days postinfection. Infected horses had significantly decreased (P < 0.05) proliferation responses as measured by thymidine incorporation to nonspecific mitogens phorbol myristate acetate (PMA) and ionomycin (I) as soon as 2 days postinfection.     

Cell-mediated immune responses in mice infected with fonsecaea pedrosoi

Time course of cellular and humoral immune responses in mice infected with Fonsecaea pedrosoi was investigated by using an antigen prepared from culture filtrate of this fungus. Mice were infected by intravenous injection with yeast-like cells of the fungus. Viable fungus was recovered from the brain of the infected mice until the 36th day after inoculation, and from the other organs examined until 14th to 16th day. Inflammatory lesions were observed in the brain, lung, heart, liver, spleen, kidney and intestine during the first 30 days after inoculation. Macrophage migration inhibition factor response in these mice was insignificant until 8 days after inoculation. A significant response was developed at day 10 and persisted until day 63. This response returned negative by 95 days after inoculation. Lymphocyte transformation response of these mice was negative until 4 days after inoculation. At day 6 blastogenic index increased to 1.5, and at day 10, 14 and 16 the indices were 1.8, 2.4 and 1.7 respectively. Precipitin response to this fungus could not be detected in these mice until 16 days after inoculation. Positive results were obtained at day 21 and lasted until 51 days after inoculation. The precipitin titers, however, did not exceed one fold in any of these mice.     

Progressive immune dysfunction in cats experimentally infected with feline immunodeficiency virus.

Within 6 months of infection with the Petaluma isolate of feline immunodeficiency virus, specific-pathogen-free domestic cats exhibited a decrease in the percentage and number of circulating CD4+ lymphocytes and in the CD4+/CD8+ T-cell ratio, along with a marginally significant depression of pokeweed mitogen-induced lymphocyte proliferation in vitro. There was no loss of responsiveness to concanavalin A during this stage, and the cats were capable of mounting a satisfactory antibody response to a T-dependent, synthetic polypeptide immunogen. The pokeweed mitogen response deficit became clearly demonstrable by 11 to 12 months postinfection. A decline in the lymphocyte proliferative response to concanavalin A and a diminished ability to mount an in vivo antibody response to the T-dependent immunogen evolved by 25 to 44 months postinfection. Virus infection did not affect the ability of cats to mount an antibody response to a T-independent synthetic polypeptide immunogen. These data indicate that feline immunodeficiency virus produces a slowly progressive deterioration of T-cell function but does not affect the ability of B cells to recognize and respond to a T-independent antigenic stimulus.     

Attenuation of inducible respiratory immune responses by oseltamivir treatment in mice infected with influenza A virus

The antiviral neuraminidase inhibitor oseltamivir (OSV) is widely used to suppress viral replication in the treatment of influenza. Here, we report that OSV administration significantly suppressed respiratory mucosal secretory IgA responses with respect to antigen (Ag)-specific antibody (Ab) production and also the induction of Ag-specific IgA Ab-forming cells, but not systemic IgG responses, in weanling mice as a model of pediatric influenza. Neutralizing activities of the airway fluids in oral OSV-treated mice were significantly less than those of sham-treated mice. Our findings suggest the risk of re-infection in patients showing a low mucosal response following OSV treatment.     

Effects of tumor necrosis factor alpha on sin nombre virus infection in vitro

Previous data indicate that immune mechanisms may be involved in developing capillary leakage during Sin Nombre virus (SNV) infection. Therefore, we investigated production of tumor necrosis factor alpha (TNF-alpha) by human alveolar macrophages and human umbilical vein endothelial cells (HUVEC) after infection with SNV. In addition, we examined the effect of TNF-alpha on HUVEC monolayer leakage. Our results reveal that although TNF-alpha decreases accumulation of viral nucleoproteins, TNF-alpha levels do not change in SNV-infected cells. In addition, supernatants from SNV-infected human alveolar macrophages did not cause a significant increase in endothelial monolayer permeability.     

Antibody and cellular immune responses to microfilarial antigens in ferrets experimentally infected with Brugia malayi

Eleven of 15 ferrets experimentally infected with Brugia malayi became amicrofilaremic after a brief patency; only four ferrets remained patent after 6 months of infection and two of these ferrets developed a high, persistent microfilaremia. Blastogenic responses of peripheral blood lymphocytes to antigens of microfilariae (mf), assayed in vitro, demonstrated an antigen sensitivity at prepatent, patent and postpatent periods of infection. Lymphocytes from ferrets with high microfilaremia had elevated background responses in culture which were directly correlated with the number of circulating mf. This background response was attributed to antigenic stimulation by mf present in the lymphocyte cultures; addition of mf to cultures of lymphocytes from postpatent ferrets induced responses equivalent to those observed in microfilaremic ferrets. Lymphocyte responses to the mitogen, concanavalin A, did not differ significantly among microfilaremic, amicrofilaremic and uninfected ferrets. Antibody in IgG to antigens of mf measured by ELISA and by immunoblots from SDS-PAGE showed similar patterns of response in ferrets which became amicrofilaremic and in the few ferrets which remained microfilaremic. prausnitz-Kustner tests demonstrated no consistent differences in titers to microfilarial antigens between patent and amicrofilaremic ferrets. The results suggest a high level of immune responsiveness to antigens of mf in infected ferrets with no evidence of immunosuppression associated with prolonged microfilaremia or of major changes in immune responses with development of amicrofilaremic infections.     

Histopathological and ultrastructural aspects of mice lungs experimentally infected with dengue virus serotype 2

Histological and ultrastructural alterations in lung tissue of BALB/c mice infected with dengue virus serotype 2 (non-neuroadapted), by intraperitoneal and intravenous routes were analyzed. Lung tissues were processed following the standard techniques for photonic and electron transmission microscopies. Histopathological and ultrastructural studies showed interstitial pneumonia, characterized by the presence of mononuclear cells. In the mouse model, the dengue virus serotype 2 seems to led to a transient inflammatory process without extensive damage to the interalveolar septa, but caused focal alterations of the blood-exchange barrier. Endothelial cells of blood capillaries exhibited phyllopodia suggesting activation by presence of dengue virus. Morphometrical analysis of mast cells showed an expressive increase of the number of these cells in peribronchiolar spaces and adjacent areas to the interalveolar septa. Alveolar macrophages showed particles dengue virus-like inside rough endoplasmic reticulum and Golgi complex, suggesting viral replication. The tissue alterations observed in our experimental model were similar to the observed in human cases of dengue fever and dengue hemorrhagic fever. Our results show that BALB/c mice are permissive host for dengue virus serotype 2 replication and therefore provides an useful model to study of morphological aspects of dengue virus infection.     

Cellular immune responses in mice infected with the intestinal nematode Trichuris muris.

CBA and B10.BR mice show variation in immune response to the intestinal nematode Trichuris muris. CBA mice develop strong resistance, eliminating worms from the intestine; B10BR mice are permissive and develop chronic infections. It is already known that resistance and permissiveness reflect differential T helper responses. The data reported here show that resistant CBA mice express good antigen-specific lymphocyte proliferative responses to infection, whereas cells from B10.BR mice are relatively anergic, although still responsive to Concanavalin A (ConA). The possibility that the altered proliferative responsiveness seen in infected B10.BR mice reflected quantitative or qualitative changes in T helper cells was examined by comparing cytokine production and expression of cell surface markers (CD4, CD8, and CD28) in mesenteric lymph node cells and spleen cells from both strains and comparing these with the characteristics of cells from resistant CBA mice and from CBA mice that had been rendered permissive to infection by a combination of irradiation and corticosteroid treatment. As expected, cells from B10.BR mice produced high levels of interferon-gamma (IFN-gamma), whereas those from CBA mice released high levels of IL-5, whether stimulated with adult worm somatic antigens, excretory/secretory antigens, or ConA. Immunosuppressed CBA mice produced high levels of both IFN-gamma and IL-5 throughout the experiment. FACS analysis revealed a decrease of CD4+ and an initial increase in CD8+ cells in all infected mice. No major changes occurred in the relative proportion of CD28(+) cells. Further evaluation of the CD28 costimulatory molecule, measured as mean fluorescence intensity, displayed down-regulation in permissive and immunosuppressed mice. The data obtained suggest that lymphocyte unresponsiveness and permissiveness to T. muris infection may be associated with a down-regulation or an initially reduced expression of costimulatory CD28 molecules.     

Eosinophil and IgE responses of IL-5 transgenic mice experimentally infected with Nippostrongylus brasiliensis.

Eosinophil and IgE responses of interleukin (IL)-5 transgenic and normal C3H/HeN mice were studied after experimental infection with Nippostrongylus brasiliensis (Nb). Intestinal worms were recovered at day 5 post-infection (PI), and numbers of total white blood cells (WBC) and eosinophils, and total serum IgE and anti-hapten (dinitrophenyl) (DNP) specific IgE titers, were measured at days 0, 14 and 21 PI. IL-5 mice appeared resistant to Nb infection showing a significantly lower worm recovery rate than normal mice (P < 0.05). Total WBC and eosinophil counts (/mm3) were significantly increased in Nb infected normal mice (P < 0.05), but unchanged (total WBC) or decreased (eosinophils) in IL-5 mice at day 21 PI. The total serum IgE level remarkably increased in normal mice, but only a little in IL-5 mice at days 14 and 21 PI. Priming with DNP brought about more remarkable increases of the total and anti-DNP specific IgE in normal mice than in IL-5 mice. The results show that IL-5 mice are resistant to Nb infection, and that eosinophil and IgE responses in these mice are not augmented by Nb infection.     

Modification of immune response in nude mice infected with mouse hepatitis virus.

In nude mice experimentally infected with mouse hepatitis virus (MHV), the numbers of early and later plaque forming cells (PFC) to sheep red blood cells (SRBC) generated in the spleen were 7 to 20 times and 2 to 163 times, respectively, greater than those in non-infected nude mice, when SRBC were given at day 0 to day 21 postinfection. Splenic theta-positive lymphocytes in infected nude mice were shown to increase only at day 10 or more postinfection. PFC response to bacterial lipopolysaccharide, a T cell-independent antigen, was not modified in MHV-infected nude mice.     

Orungo virus: organ distribution with histopathology and development of experimentally infected Swiss albino mice

The organ distribution and pathogenecity of Orungo virus were studied in Swiss Albino mice following intracerebral and intraperitoneal inoculations. There was an age-related response in mice to Orungo virus ic infection. Virus multiplied to higher titres in the brain of newborn (2-day-old) mice than in the other organs. The histopathologic changes which were restricted to the brain included diffuse mononuclear cell infiltration, prominent perivascular and interstitial oedema in the cerebrum and cerebellum. In 10-day-old mice, low level infective virus was detected only in the brain, with resultant mild and focal mononuclear cell infiltration in the cerebral cortex. Recovery from Orungo virus ic infection in 10-day-old animals is accompanied by stunted growth. Orungo virus did not multiply in 21-day-old mice which were found to be histologically unremarkable. Following ip inoculation Orungo virus did not multiply, nor was there an histopathological change in inoculated newborn, 10-day or 21-day-old mice.     

Cellular and molecular immune responses of the sea bass (Dicentrarchus labrax) experimentally infected with betanodavirus

Naïve sea bass juveniles (38.4 ± 4.5 g) were intramuscularly infected with a sublethal dose of betanodavirus isolate 378/I03, followed after 43 days by a similar boosting. This infection resulted in an overall mortality of 7.6%. At various intervals, sampling of fish tissues was performed to investigate: i) B and T lymphocyte content in organs and tissues; ii), proliferation of leucocytes re-stimulated in vitro with inactivated virus; iii) presence of serum antibody specific for betanodavirus; iv) expression of genes coding for the following immunoregulatory molecules involved in innate and acquired responses: type I IFN, Mx, IL-1, Cox-2; IL-10, TGF-β, TCRβ, CD4, CD8α, IgM, by using a quantitative PCR array system developed for sea bass.The obtained results showed a detectable increase of T cells and B cells in PBL during betanodavirus infection. Furthermore, leucocytes obtained from blood, head kidney, and gills showed a detectable “in vitro” increase in viability upon addition of inactivated viral particles, as determined by measuring intracellular ATP concentration. ELISA analysis of sera showed that exposure to nodavirus induced a low, but specific antibody titer measured 43 days after infection, despite the presence of measurable levels of natural antibody. Finally, a strong upregulation of genes coding for type I IFN, Mx, and IgM was identified after both infection and boosting. Interestingly, an upregulation of Cox-2 until boosting, and of TGF-β and IL-10 after boosting was also observed, while the other tested genes did not show any significant variations with respect to mock-treated fish. Overall, our work represents a first comprehensive analysis of cellular and molecular immune parameters in a fish species exposed to a pathogenic virus.