Body weight changes of mice with different immunity to Sendai virus after challenge infection

Four groups of mice immunized with Sendai virus in different ways, namely convalescent (CT), intrapertoneally (IP) or intranasally (IN) immunized with the inactivated virus and non-immunized (NOI), were challenged and examined degree of immunity and body weight changes. Degree of immunity assessed based on the antibodies, the lung lesions and the lung viral titers was higher in order of CT, IP, IN and NOI. Body weight changes, expressed by both the decrease in mean body weights and the correlation coefficients between pre- and post-challenge, were less in the mice with higher immunity against Sendai virus.     

Sendai virus infection of mice with protein malnutrition.

Sendai virus pneumonia was produced in BALB/c mice fed protein-deficient diets in an effort to understand the severity of viral pneumonia in infants in developing countries. Animals on the deficient diet became clinically malnourished, and some aspects of cellular immunity were altered. In protein-deprived animals, the 50% lethal dose of intranasally administered Sendai virus was over 1,000-fold lower, pulmonary virus titers were higher, the infection was prolonged, and lung infection was established at a lower inoculum than in normal animals.     

Resistance of mice with active and maternally passive immunity against Sendai virus

Resistance of mice with active and maternally passive immunity to Sendai virus infection was investigated. Mice with active immunization were convalescent ones from intranasal infection with 10(3) TCID50 of the virus [CT], ones immunized with 4 weekly intranasal injections of about 4 X 10(3) hemagglutinating units (HAU) of formalin-inactivated virus (FV) [IN], or ones immunized with 4 weekly intraperitoneal injections of about 2 X 10(3) HAU of FV [IP]. The serum neutralizing (NT) antibody titers ranged 1 : 10 to 1 : 20 in CT and IN, and 1 : 20 to 1 : 40 in IP at 4 weeks after initial immunization. NT antibody in the lung lavage was detected only in IP in 3/5. After intranasal challenge infection with 10(6) TCID50 of the virus, little or no gross lung lesion, no virus recovery and no body weight loss were observed throughout experiment, in these 3 immunized groups, whereas, control mice showed lung lesions in 4/5 (7 days), virus recovery in 4/5 at 3 days and in 1/5 at 7 days post-challenge, and body weight loss. In additional histological study, bronchiolar epithelial methaplasia and alveolar septal thickening, which were characteristic findings in non-immunized infected mice, were not observed in mice immunized with 2 biweekly injection of about 250 HA of FV and then challenged. Maternal immunity was investigated in offsprings from convalescent dams infected with 10(3) TCID50 at mating [mCT] and from dams immunized intraperitoneally with 4 X 10(3) HAU of FV at 0, 1 and 2 weeks after mating and, 1 and 2 weeks after parturition [mIP]. Serum NT antibody was not detected in mCT, but the titers ranging 1 : 20 to 1 : 40 were detected in mIP. After intranasal challenge of mCT, mIP and offsprings from non-immune mice with 10(3) TCID50 of the virus, virus recovery on day 3 was 2/4, 1/4 and 3/3, and incidence of total lung lesions on day 7 and 12 was 11/21, 2/13 and 16/16, respectively. Body weight gain was suppressed slightly in the immune groups but markedly in the non-immune control.     

Sendai virus infection induces efficient adaptive immunity independently of type I interferons

Adaptive immunity in response to virus infection involves the generation of Th1 cells, cytotoxic T cells, and antibodies. This type of immune response is crucial for the clearance of virus infection and for long-term protection against reinfection. Type I interferons (IFNs), the primary innate cytokines that control virus growth and spreading, can influence various aspects of adaptive immunity. The development of antiviral immunity depends on many viral and cellular factors, and the extent to which type I IFNs contribute to the generation of adaptive immunity in response to a viral infection is controversial. Using two strains (Cantell and 52) of the murine respiratory Sendai virus (SeV) with differential abilities to induce type I IFN production from infected cells, together with type I IFN receptor-deficient mice, we examined the role of type I IFNs in the generation of adaptive immunity. Our results show that type I IFNs facilitate virus clearance and enhance the migration and maturation of dendritic cells after SeV infection in vivo; however, soon after infection, mice clear the virus from their lungs and efficiently generate cytotoxic T cells independently of type I IFN signaling. Furthermore, animals that are unresponsive to type I IFN develop long-term anti-SeV immunity, including CD8+ T cells and antibodies. Significantly, this memory response is able to protect mice against challenge with a lethal dose of virus. In conclusion, our results show that primary and secondary anti-SeV adaptive immunities are developed normally in the absence of type I IFN responsiveness.     

Interferon-dependent immunity is essential for resistance to primary dengue virus infection in mice, whereas T- and B-cell-dependent immunity are less critical

Dengue virus (DEN) causes dengue fever and dengue hemorrhagic fever/dengue shock syndrome, which are major public health problems worldwide. The immune factors that control DEN infection or contribute to severe disease are neither well understood nor easy to examine in humans. In this study, we used wild-type and congenic mice lacking various components of the immune system to study the immune mechanisms in the response to DEN infection. Our results demonstrate that alpha/beta interferon (IFN-α/β) and IFN-γ receptors have critical, nonoverlapping functions in resolving primary DEN infection. Furthermore, we show that IFN-α/β receptor-mediated action limits initial DEN replication in extraneural sites and controls subsequent viral spread into the central nervous system (CNS). In contrast, IFN-γ receptor-mediated responses seem to act at later stages of DEN disease by restricting viral replication in the periphery and eliminating virus from the CNS. Mice deficient in B, CD4⁺ T, or CD8⁺ T cells had no increased susceptibility to DEN; however, RAG mice (deficient in both B and T cells) were partially susceptible to DEN infection. In summary, (i) IFN-α/β is critical for early immune responses to DEN infection, (ii) IFN-γ-mediated immune responses are crucial for both early and late clearance of DEN infection in mice, and (iii) the IFN system plays a more important role than T- and B-cell-dependent immunity in resistance to primary DEN infection in mice.     

IRF-3 activation by Sendai virus infection is required for cellular apoptosis and avoidance of persistence

Here, we report that specific manipulations of the cellular response to virus infection can cause prevention of apoptosis and consequent establishment of persistent infection. Infection of several human cell lines with Sendai virus (SeV) or human parainfluenza virus 3, two prototypic paramyxoviruses, caused slow apoptosis, which was markedly accelerated upon blocking the action of phosphatidylinositol 3-kinases (PI3 kinases) in the infected cells. The observed apoptosis required viral gene expression and the action of the caspase 8 pathway. Although virus infection activated PI3 kinase, as indicated by AKT activation, its blockage did not inhibit JNK activation or IRF-3 activation. The action of neither the Jak-STAT pathway nor the NF-kappaB pathway was required for apoptosis. In contrast, IRF-3 activation was essential, although induction of the proapototic protein TRAIL by IRF-3 was not required. When IRF-3 was absent or its activation by the RIG-I pathway was blocked, SeV established persistent infection, as documented by viral protein production and infectious virus production. Introduction of IRF-3 in the persistently infected cells restored the cells' ability to undergo apoptosis. These results demonstrated that in our model system, IRF-3 controlled the fate of the SeV-infected cells by promoting apoptosis and preventing persistence.     

Utility of immunofluorescence for detection of Sendai virus infection during quarantine of mice and rats

The detection rates of Sendai virus antigen in the lung and tracheal mucosa by immunofluorescence were comparable to those of virus isolation by chick embryos and seemed to be useful during the quarantine of mice and rats.     

Effect of acute or daily cocaine administration on cellular immune response and virus infection in mice

The effects of in vivo cocaine administrations on cellular cytotoxicity were studied. Cocaine induced a dose-related immunosuppression of natural killer cell activity, with maximal depression at 1-5 mg/kg. In addition, the degree of inhibition following a single intraperitoneal (i.p.) or intravenous cocaine dose (acute treatment, 1 mg/kg) was similar to that after repeated administration (subchronic treatment: 1 mg/kg/day i.p. for 7 consecutive days or subcutaneous administration by Alzet 2001 osmotic minipumps). T cells from cocaine-treated mice failed to generate cytotoxic T lymphocytes (CTL) in mixed lymphocyte cultures and acute or subchronic cocaine treatment also inhibited CTL generation in vivo. On the other hand, acute administration induced a very rapid (24-hour) inhibition of natural cytotoxicity, with a return to normal within 72 h after treatment. By contrast, repeated doses led to more protracted immunologic consequences and a delayed recovery (144 h). The effect of cocaine on susceptibility to influenza virus (PR8) infection was also investigated. Both acute and subchronic treatment significantly decreased resistance to PR8 infection. The results clearly indicate that cocaine has a potent suppressive effect on cellular immunity and that abuse can adversely affect the outcome of infectious diseases.     

Distinctive cellular immunity in genetically susceptible BALB/c mice recovered from Leishmania major infection or after subcutaneous immunization with killed parasites

Genetically susceptible BALB/c mice are refractory to further infection after recovery from Leishmania major infection after a sublethal dose of gamma-irradiation. In contrast, mice immunized with killed promastigotes s.c. develop exacerbated lesions after infection. Both groups of mice produce only a low level of specific antibody and no detectable cytotoxic T cells, but do have a strong antigen-specific DTH, which is adoptively transferable with Lyt-1+2-, L3T4+ T cells. Kinetic and histological studies revealed that mice immunized s.c. developed Jones-Mote hypersensitivity, peaking at 15 hr. with little mononuclear cell infiltration at the site of antigen administration; whereas mice that had recovered from infection developed tuberculin-type of reactivity, peaking at 24 to 48 hr, with intense mononuclear cell infiltration. Splenic T cells from recovered mice, when injected into the footpads of normal recipients together with live promastigotes, were able to retard lesion development; whereas T cells from s.c. immunized mice, when similarly transferred, accelerated disease progression. Antigen-specific culture supernatant of spleen cells from recovered mice also activated normal resident peritoneal macrophages to kill intracellular L. major amastigotes and tumor cells. Culture supernatants of spleen cells from s.c. immunized or normal mice were devoid of such activities. Part of the macrophage-activating potential can be inhibited by antibody specific for IFN-gamma. These results therefore demonstrate that whereas the Jones-Mote reaction is correlated with disease exacerbation, the tuberculin-type of DTH may be protective. Furthermore, in vivo immunity is directly related to the capacity of T cells to produce macrophage-activating factor.     

Cellular and humoral immunity against vaccinia virus infection of mice

Despite the widespread use of vaccinia virus (VV) as a vector for other Ags and as the smallpox vaccine, there is little information available about the protective components of the immune response following VV infection. In this study, protection against wild-type VV was evaluated in mice with respect to the relative contributions of CD8(+) T cells vs that of CD4(+) T cells and Ab. C57BL/6 mice primed with the Western Reserve strain of VV mount significant IgM and IgG Ab responses, specific cytotoxic T cell responses, IFN-gamma responses in CD4(+) and CD8(+) T cells, and effectively clear the virus. This protection was abrogated by in vivo depletion of CD4(+) T cells or B cells in IgH(-/-) mice, but was not sensitive to CD8(+) T cell depletion alone. However, a role for CD8(+) T cells in primary protection was demonstrated in MHC class II(-/-) mice, where depleting CD8(+) T cells lead to increase severity of disease. Unlike control MHC class II(-/-) mice, the group depleted of CD8(+) T cells developed skin lesions on the tail and feet and had adrenal necrosis. Adoptive transfer experiments also show CD8(+) T cells can mediate protective memory. These results collectively show that both CD4(+) and CD8(+) T cell-mediated immunity can contribute to protection against VV infection. However, CD4(+) T cell-dependent anti-virus Ab production plays a more important role in clearing virus following acute infection, while in the absence of Ab, CD8(+) T cells can contribute to protection against disease.     

Dipeptidyl peptidase I-dependent neutrophil recruitment modulates the inflammatory response to Sendai virus infection

The role of innate immunity in the pathogenesis of asthma is unclear. Although increased presence of neutrophils is associated with persistent asthma and asthma exacerbations, how neutrophils participate in the pathogenesis of asthma remains controversial. In this study, we show that the absence of dipeptidyl peptidase I (DPPI), a lysosomal cysteine protease found in neutrophils, dampens the acute inflammatory response and the subsequent mucous cell metaplasia that accompanies the asthma phenotype induced by Sendai virus infection. This attenuated phenotype is accompanied by a significant decrease in the accumulation of neutrophils and the local production of CXCL2, TNF, IL-1beta, and IL-6 in the lung of infected DPPI-/- mice. Adoptive transfer of DPPI-sufficient neutrophils into DPPI-/- mice restored the levels of CXCL2 and enhanced cytokine production on day 4 postinfection and subsequent mucous cell metaplasia on day 21 postinfection. These results indicate that DPPI and neutrophils play a critical role in Sendai virus-induced asthma phenotype as a result of a DPPI-dependent neutrophil recruitment and cytokine response.     

IL-10 regulates viral lung immunopathology during acute respiratory syncytial virus infection in mice

Interleukin (IL-) 10 is a pleiotropic cytokine with broad immunosuppressive functions, particularly at mucosal sites such as the intestine and lung. Here we demonstrate that infection of BALB/c mice with respiratory syncytial virus (RSV) induced IL-10 production by CD4(+) and CD8(+) T cells in the airways at later time points (e.g. day 8); a proportion of these cells also co-produced IFN-γ. Furthermore, RSV infection of IL-10(-/-) mice resulted in more severe disease with enhanced weight loss, delayed recovery and greater cell infiltration of the respiratory tract without affecting viral load. In addition, IL-10(-/-) mice had a pronounced airway neutrophilia and heightened levels of pro-inflammatory cytokines and chemokines in the bronchoalveolar lavage fluid. Notably, the proportion of lung T cells producing IFN-γ was enhanced, suggesting that IL-10 may act in an autocrine manner to dampen effector T cell responses. Similar findings were made in mice treated with anti-IL-10R antibody and infected with RSV. Therefore, IL-10 inhibits disease and inflammation in mice infected with RSV, especially during recovery from infection.     

Stimulation of the cellular immune response to lymphocytic choriomeningitis (LCM) virus infection in suckling mice

Death occurred earlier and its rate was higher in one-week-old mice treated with phytohaemagglutinin (PHA) and subsequently inoculated intracerebrally with LCM virus than in their virus infected but untreated littermates. Thus PHA treatment contributed to the outcome of LCM virus infection in the form of lethal meningitis. The course of LCM virus infection in 1-week-old PHA treated mice was similar as in the untreated 2-week-old mice. This indicates that PHA treatment accelerated the development of cell mediated immunological capacity in suckling mice.     

The role of maternal antibody in contact infection of mice with Sendai virus.

To study the role of maternal antibody in infection with Sendai virus in mice, maternally immune and non-immune mice, aged 4 to 5 weeks, were placed in cages with infector mice and the cages were kept for 19 days in a vinyl isolator. Neither increase of hemagglutination inhibiting antibody titers nor gross pulmonary lesions was recognized on the immune mice during the observation period in contrast with the non-immune mice. However, the multiplication of the virus in their respiratory tracts was the same or slightly low as compared with that of non-immune mice.     

Experimental Sendai virus infection in laboratory rats. I. Virus replication and immune response

Sixty 5 to 8 week old Sprague-Dawley (Crl:CD(SD)BR) rats were inoculated intranasally with 2000 egg infectious doses of egg-propagated Sendai virus. Virus was recovered from the upper respiratory tract and lungs on days 1 through 8 post-inoculation (PI). Serum antibody responses were measured for 12 rats over a 9 month period PI. Antibody was first detected at 7 days, peaked at 21 days, and was detected in 5 of the 12 rats at 9 months. A cell-mediated response, as measured by lymphocyte blastogenesis, also was detected at 7 days and peaked at 21 days, but was not detected at 6 months PI. Lung and serum interferon (IFN) was first detected at 3 hours and peaked at 6 hours, but was not detected by 160 hours. Lung IFN levels were 4 to 10 times those in the serum. These studies indicate that pathogenesis of Sendai virus infection in the rat is similar to that reported in the mouse, but that there are differences in the kinetics of both viral replication and morphologic changes, as described in the companion paper.     

Roles of target cells and virus-specific cellular immunity in primary simian immunodeficiency virus infection

There is an ongoing debate on whether acute human immunodeficiency virus infection is controlled by target cell limitation or by virus-specific cellular immunity. To resolve this question, we developed a novel mathematical modeling scheme which allows us to incorporate measurements of virus load, target cells, and virus-specific immunity and applied it to a comprehensive data set generated in an experiment involving rhesus macaques infected with simian immunodeficiency virus. Half of the macaques studied were treated during the primary infection period with reagents which block T-cell costimulation and as a result displayed severely impaired virus-specific immune responses. Our results show that early viral replication in normal infection is controlled to a large extent by virus-specific CD8(+) T cells and not by target cell limitation.