Cell-mediated protection against pulmonary Yersinia pestis infection

Pulmonary infection with the bacterium Yersinia pestis causes pneumonic plague, an often-fatal disease for which no vaccine is presently available. Antibody-mediated humoral immunity can protect mice against pulmonary Y. pestis infection, an experimental model of pneumonic plague. Little is known about the protective efficacy of cellular immunity. We investigated the cellular immune response to Y. pestis in B-cell-deficient microMT mice, which lack the capacity to generate antibody responses. To effectively prime pulmonary cellular immunity, we intranasally vaccinated microMT mice with live replicating Y. pestis. Vaccination dramatically increased survival of microMT mice challenged intranasally with a lethal Y. pestis dose and significantly reduced bacterial growth in pulmonary, splenic, and hepatic tissues. Vaccination also increased numbers of pulmonary T cells, and administration of T-cell-depleting monoclonal antibodies at the time of challenge abrogated vaccine-induced survival. Moreover, the transfer of Y. pestis-primed T cells to naive microMT mice protected against lethal intranasal challenge. These findings establish that vaccine-primed cellular immunity can protect against pulmonary Y. pestis infection and suggest that vaccines promoting both humoral and cellular immunity will most effectively combat pneumonic plague.     

Cellular but not humoral immune responses generated by vaccination with dendritic cells protect mice against leukaemia

Dendritic cells (DC) are extremely efficient at generating both prophylactic and therapeutic anti‐tumour immunity. We aimed to analyse the respective roles of humoral and cellular immune responses generated in mice vaccinated with bone marrow (BM)‐derived DC in terms of in vivo anti‐leukaemia effect. We used the murine L1210 B lymphocytic leukaemia genetically modified to express on the cell surface of human CD4 (hCD4) (L1210/hCD4) as a model tumour‐associated antigen (TAA). DC cultures were loaded with either purified soluble hCD4 (shCD4) protein or unfractionated L1210/hCD4 extracts and injected as vaccine into mice. The efficacy of these vaccinations was compared with that of vaccination with shCD4 protein emulsified in Freund’s adjuvant (FA). We evaluated the immune responses generated after these vaccinal protocols and the survival rate of vaccinated mice subsequently challenged with a lethal injection of L1210/hCD4 cells. Our results demonstrated that vaccination with shCD4 protein or tumour extract‐loaded DC mainly generated an hCD4 antigen‐specific cell‐mediated cytotoxic immune response that was associated with a specific protection against leukaemia. In contrast, vaccination with the protein emulsified in FA only generated potent humoral immune responses that were not protective against leukaemia. Altogether, our results indicate that the unique property of loaded DC to trigger an anti‐leukaemia protective effect is mainly associated with cellular immune responses.     

The effect of humoral and cell-mediated immunity in resistance to systemic Serratia infection.

Protection against experimental Serratia marcescens infection in mice was enhanced by prior injection of formalin-killed or viable bacteria of the same strain. From the first to the fourth week after vaccination, specific immunity was involved in the host defence against systemic serratia infection. The transfer of antiserum specific for S. marcescens increased bacterial clearance from the liver, but did not increase the survival of the mice. Bacterial clearance from the liver was also increased by the transfer of spleen cells from immunised mice, but, again, survival was not increased. However, the transfer of both antiserum and spleen cells from vaccinated mice increased both bacterial clearance from the liver and survival (p less than 0.01). These results suggest an additive effect of humoral immunity and T-cell-mediated immunity in protection against systemic serratia infection.     

Timing of retroviral infection influences anamnestic immune response in vaccinated primates

Using simian immunodeficiency virus (SIV) infection of rhesus macaques to model human immunodeficiency virus (HIV) infection of humans, we assessed whether broadly reactive vaccine-induced humoral immunity would remain broadly reactive after viral challenge, and whether there would be significant differences in anamnestic antibody responses if animals were challenged when predominately effector or memory lymphocyte populations were present. Animals immunized over a prolonged period and challenged 11 months after vaccination mounted more broadly reactive and stronger humoral immunity than those rapidly vaccinated and challenged 2 weeks after their final vaccinations. These data suggest that vaccination schedule and the timing of virus challenge should be considered when evaluating future candidate HIV vaccines.     

The effect of T and B lymphocyte depletion on the protection of mice vaccinated with a Gal E mutant of Salmonella typhimurium.

Immunosuppressive agents were used to determine the relative importance of T and B lymphocytes in conferring protection to mice vaccinated with a live gal E mutant of Salmonella typhimurium, strain G30D. Lymphocyte transformation and serum agglutination tests showed that while cyclophosphamide (CPA) suppressed B lymphocytes, antilymphocyte sea (ALS) suppressed both T and B cells. The humoral response of vaccinated animals treated with ALS was therefore supplemented by the i.v. injection of serum from untreated vaccinated mice. CPA-treated mice could not control multiplication of the vaccinal strain which eventually killed them. There was little multiplication of the vaccinal strain in the controls and ALS-treated mice, all of which survived to challenge. The vaccinated controls and vaccinated ALS treated groups each survived infection with the challenge strain which was gradually eliminated. It was concluded that humoral immunity was of greater importance than cellular immunity in mice vaccinated i.p. with strain G30D.     

A DNA vaccine encoding lumazine synthase from Brucella abortus induces protective immunity in BALB/c mice

This study was conducted to evaluate the immunogenicity of the Brucella abortus lumazine synthase (BLS) gene cloned into the pcDNA3 plasmid, which is driven by the cytomegalovirus promoter. Injection of plasmid DNA carrying the BLS gene (pcDNA-BLS) into BALB/c mice elicited both humoral and cellular immune responses. Antibodies to the encoded BLS included immunoglobulin G1 (IgG1) IgG2a, IgG2b, IgG3, and IgM isotypes. Animals injected with pcDNA-BLS exhibited a dominance of IgG2a over IgG1. In addition, spleen cells from vaccinated animals produced interleukin-2 and gamma interferon but not IL-10 or IL-4 after in vitro stimulation with recombinant BLS (rBLS), suggesting the induction of a Th1 response. Protection was evaluated by comparing the levels of infection in the spleens of vaccinated mice challenged with B. abortus 544. Immunization with pcDNA-BLS- reduced the bacterial burden relative to those in the control groups. Mice immunized with rBLS produced a significant humoral response but did not show a specific cellular response or any protection from challenge. Altogether, these data suggest that pcDNA-BLS is a good immunogen for the production of humoral and cell-mediated responses in mice and is a candidate for use in future studies of vaccination against brucellosis.     

弓形虫多表位DNA疫苗的构建及其免疫保护作用

目的:构建弓形虫多表位DNA疫苗并研究其免疫保护效果.方法:将编码含弓形虫多个T、B细胞表位的6段弓形虫多肽基因,以5个甘氨酸编码基因相间隔相连接,克隆入真核表达质粒pcDNA3.1( )中,构建成多表位弓形虫DNA疫苗.免疫BALB/c小鼠,测定其诱导的特异性抗体水平及T淋巴细胞增殖状况,同时进行弓形虫攻击感染保护实验.结果:成功构建了包含多个弓形虫表位的真核表达质粒pcDNA3.1/T-ME,以其作为DNA疫苗免疫小鼠,可诱导机体产生弓形虫特异性的体液及细胞免疫应答,产生有效的抗弓形虫保护性免疫应答.结论:构建的弓形虫多表位DNA疫苗能诱导机体产生有效的保护性免疫应答,在控制弓形虫感染上具有可行性.     

Maternal antibody inhibits both cellular and humoral immunity in response to measles vaccination at birth

Maternal antibody prevents the use of live, attenuated measles vaccine (LAV) before 6-9 months of age, but vaccinated 6-month-old infants can mount a T cell response. An infant macaque model was used to study the immune response to LAV in the newborn in the presence or absence of maternal antibody. Four newborn monkeys without detectable maternal antibody and 9 newborns with passive measles antibody were vaccinated with LAV. Only the infants without passive antibody seroconverted after vaccination and 3 of 4 of these infants also developed measles-specific interferon gamma+ T cells. The monkeys were challenged with wild-type measles virus at 5 months of age, and 7 of 9 infants vaccinated in the presence of passive antibody had systemic infection and skin rash, while 3 of the 4 infants vaccinated in the absence of passive antibody were protected from viremia and rash. This suggests that the newborn can respond to LAV but that maternal antibody suppresses the priming of both humoral and cellular immunity at birth.     

Effective immunization against Bordetella pertussis respiratory infection in mice is dependent on induction of cell-mediated immunity.

A murine respiratory challenge model was used to examine the induction of cellular and humoral immune responses and their role in protection against Bordetella pertussis following immunization or previous infection. Spleen cells from mice convalescing from a B. pertussis infection exhibited extensive in vitro T-cell proliferation and secreted high levels of interleukin-2 (IL-2) and gamma interferon but not IL-4 or IL-5, a cytokine profile typical of CD4+ Th1 cells. Serum from these mice had low or undetectable anti-B. pertussis antibody levels. In contrast, mice immunized with an acellular pertussis vaccine had high levels of B. pertussis antibodies and spleen cells secreting IL-5 but not gamma interferon, a profile characteristic of CD4+ Th2 cells. Immunization with an inactivated whole-cell vaccine induced both CD4+ Th1 and serum antibody responses. After exposure to a B. pertussis respiratory challenge, the convalescent mice and those immunized with the whole-cell vaccine eliminated the bacterial infection significantly faster than mice immunized with the acellular vaccine. These findings show that the selection of antigens and their form of presentation are important in determining whether the subsequent immune response is cellular, mediated by Th1 cells, or humoral, mediated by Th2 cells. In the murine model, the induction of a Th1-mediated cellular immune response appears to be a key element in acquired immunity to a B. pertussis infection.     

Antibody-mediated elimination of the obligate intracellular bacterial pathogen Ehrlichia chaffeensis during active infection

It is generally accepted that cellular, but not humoral immunity, plays an important role in host defense against intracellular bacteria. However, studies of some of these pathogens have provided evidence that antibodies can provide immunity if present during the initiation of infection. Here, we examined immunity against infection by Ehrlichia chaffeensis, an obligate intracellular bacterium that causes human monocytic ehrlichiosis. Studies with mice have demonstrated that immunocompetent strains are resistant to persistent infection but that SCID mice become persistently and fatally infected. Transfer of immune serum or antibodies obtained from immunocompetent C57BL/6 mice to C57BL/6 scid mice provided significant although transient protection from infection. Bacterial clearance was observed when administration occurred at the time of inoculation or well after infection was established. The effect was dose dependent, occurred within 2 days, and persisted for as long as 2 weeks. Weekly serum administration prolonged the survival of susceptible mice. Although cellular immunity is required for complete bacterial clearance, the data show that antibodies can play a significant role in the elimination of this obligate intracellular bacterium during active infection and thus challenge the paradigm that humoral responses are unimportant for immunity to such organisms.     

Inability of spleen cells from chancre-immune rabbits to confer immunity to challenge with Treponema pallidum.

Although several lines of evidence suggest that cellular immune mechanisms play a role in controlling infection due to Treponema pallidum, recent studies have shown that induction of acquired cellular resistance by antigenically unrelated organisms fails to protect rabbits against syphilitic infection, thereby casting doubt on this hypothesis. In the present paper we describe attempts to transfer immunity to syphilis by using spleen cells from chancre-immune rabbits. Intravenous infusion of 2 X 10(8) spleen lymphocytes was capable of transferring acquired cellular resistance to Listeria and delayed hypersensitivity to tuberculin. However, in eight separate experiments using outbred or inbred rabbits, 2 X 10(8) spleen cells from syphilis-immune animals failed to confer resistance to T. pallidum whether by intravenous or intradermal challenge. Mixing immune lymphocytes with treponemes immediately before intradermal inoculation also failed to confer resistance. Despite the fact that syphilitic infection stimulates cellular immune mechanisms and induces acquired cellular resistance to antigenically unrelated organisms, cellular immunity may not play an important role in immunity to syphilis.     

Role of systemic and mucosal immune responses in reciprocal protection against Bordetella pertussis and Bordetella parapertussis in a murine model of respiratory infection

The roles of systemic humoral immunity, cell-mediated immunity, and mucosal immunity in reciprocal protective immunity against Bordetella pertussis and Bordetella parapertussis were examined by using a murine model of respiratory infection. Passive immunization with serum from mice infected with B. pertussis established protective immunity against B. pertussis but not against B. parapertussis. Protection against B. parapertussis was induced in mice that had been injected with serum from mice infected with B. parapertussis but not from mice infected with B. pertussis. Adoptive transfer of spleen cells from mice infected with B. pertussis or B. parapertussis also failed to confer reciprocal protection. To examine the role of mucosal immunity in reciprocal protection, mice were infected with preparations of either B. pertussis or B. parapertussis, each of which had been incubated with the bronchoalveolar wash of mice that were convalescing after infection with B. pertussis or B. parapertussis. Such incubation conferred reciprocal protection against B. pertussis and B. parapertussis on infected mice. The data suggest that mucosal immunity including secreted immunoglobulin A in the lungs might play an important role in reciprocal protective immunity in this murine model of respiratory infection.     

Acquired cell-mediated protection in rainbow trout,Oncorhynchus mykiss,against the haemoflagellate,Cryptobia salmositica

Disease-free rainbow trout, Oncorhynchus mykiss (Walbaum),were inoculated with either the pathogenic Cryptobia salmositica Katz, 1951 or with the attenuated vaccine strain of the parasite. A number of vaccinated fish were then challenged at 6 weeks post-vaccination with pathogenic C. salmositica. Respiratory burst activity in stimulated macrophages (isolated from infected or vaccinated fish) was demonstrated by detection of released super-oxide anions, and the protein contents in these cells were also determined after the cells were digested. At 5 weeks after infection, the respiratory burst activity of macrophages from infected fish was significantly higher than those in naive and vaccinated fish. In addition, macrophages from vaccinated fish had greater activity than naive fish. Macrophage activity in vaccinated and challenged fish was comparable to that of infected fish. Antibodies were detected (ELISA) at 3 weeks after vaccination and at 5 weeks in infected fish. Complement-fixing antibodies (immune lysis test) were detected in infected fish at 5 weeks post-infection but were not detected in vaccinated fish unless they were challenged with the pathogen, in which case the titre rose rapidly.     

Adenoviral expression of a truncated S1 subunit of SARS-CoV spike protein results in specific humoral immune responses against SARS-CoV in rats

The causative agent of severe acute respiratory syndrome (SARS) has been identified as SARS-associated coronavirus (SARS-CoV), but the prophylactic treatment of SARS-CoV is still under investigation. We constructed a recombinant adenovirus containing a truncated N-terminal fragment of the SARS-CoV Spike (S) gene (from--45 to 1469, designated Ad-S(N)), which encoded a truncated S protein (490 amino-acid residues, a part of 672 amino-acid S1 subunit), and investigated whether this construct could induce effective immunity against SARS-CoV in Wistar rats. Rats were immunized either subcutaneously or intranasally with Ad-S(N) once a week for three consecutive weeks. Our results showed that all of the immunized animals generated humoral immunity against the SARS-CoV spike protein, and the sera of immunized rats showed strong capable of protecting from SARS-CoV infection in vitro. Histopathological examination did not find evident side effects in the immunized animals. These results indicate that an adenoviral-based vaccine carrying an N-terminal fragment of the Spike gene is able to elicit strong SARS-CoV-specific humoral immune responses in rats, and may be useful for the development of a protective vaccine against SARS-CoV infection.     

Effect of metabolic inhibitors on the formation of antibody to sheep erythrocytes, on development of delayed hypersensitivity, and on the immune response to infection with Mycobacterium tuberculosis in mice.

The effect of a number of metabolic inhibitors was determined on: (i) the production of cellular immunity to infection with Mycobacterium tuberculosis in mice by vaccination with mycobacterial ribonucleic acid (RNA), (Ii) the production of cellular immunity to infection with M. tuberculosis in mice with viable H37Ra cells, (iii) the induction of antibody formation to sheep erythrocytes, and (iv) the induction of delayed hypersensitivity in mice to purified protein derivative. The pattern of inhibition produced by metabolic inhibitors on cellular immunity to infection with M. tuberculosis produced by mycobacterial RNA was entirely different from the pattern of inhibition produced by the same metabolic inhibitors on antibody formation to sheep erythrocytes. The effect of the metabolic inhibitors on the induction of delayed hypersensitivity to purified protein derivative did not correlate with the pattern of inhibition produced by the same compounds on antibody formation or on the development of immunity produced by mycobacterial RNA. Cellular immunity to infection produced in mice by viable H37Ra cells was not reduced by any of the metabolic inhibitors except actinomycin D. The possible reasons for the lack of activity of the metabolic inhibitors on the immune response to viable H37Ra cells and the lack of correlation with the pattern of inhibition found in mice vaccinated with mycobacterial RNA is discussed.     

Host defenses in experimental scrub typhus: role of cellular immunity in heterologous protection.

The relative contributions of cellular and humoral immunity in scrub typhus infections were studied in inbred mice employing paired strains of Rickettsia tsutsugamushi differing in virulence. An infectious dose (100 MID50) of the less virulent Gilliam strain resulted in heterologous immune protection against an otherwise lethal challenge (1,000 MLD50) of the virulent Karp strain. Partial heterologous protection against lethal Karp challenge was observed in animals preimmunized with the Gilliam strain as early as 3 days prior to challenge, whereas complete protection against illness and death existed in animals immunized at least 7 days prior to challenge. In the heterologous protection provided by prior Gilliam infection, the role of humoral immunity was not of primary importance for the following reasons: (i) significant levels of complement-fixing antibody against R. tsutsugamushi were not detectable until long after animals were solidly immune; (ii) antibody eventually appearing after Gilliam immunization exhibited a consistently low complement-fixing titer against the immunizing homologous (Gilliam) strain and contained no detectable activity against the heterologous challenge (Karp) strain; and (iii) passive transfer of large quantities of serum from Gilliam immune mice, themselves immune to Karp challenge, failed to protect recipients against a similar challenge. However, protection was afforded by the passive transfer of serum containing antibody against Karp, suggesting a major role for antibody in protection against homologous infection. This heterologous challenge system was particularly useful because it minimized the role of humoral immunity, at least early in the course of infection, and allowed a definitive examination of the cellular response. Cell-mediated immunity played a major role in the heterologous protection observed after Gilliam immunization. This was evidenced by the significant protection against Karp challenge afforded by the passive transfer of spleen cells from animals immunized with Gilliam 7 to 63 days previously. Of the immune spleen cells, only those which were nonadherent, presumably lymphocytes, were capable of transferring passive heterologous protection. This protective effect of nonadherent cells could be ablated by depleting the cell population of thymus-derived or T cells with anti-theta serum and complement prior to transfer but not by use of anti-immunoglobulin serum and complement, which selectively removes bone marrow-derived or B cells. These results suggested that the cell in immune spleens capable of conferring heterologous protection was a T lymphocyte.     

Protection against a lethal H5N1 influenza challenge by intranasal immunization with virus-like particles containing 2009 pandemic H1N1 neuraminidase in mice

Highly pathogenic H5N1 influenza shares the same neuraminidase (NA) subtype with the 2009 pandemic (H1N1pdm09), and cross-reactive NA immunity might protect against or mitigate lethal H5N1 infection. In this study, mice were either infected with a sublethal dose of H1N1pdm09 or were vaccinated and boosted with virus-like particles (VLP) consisting of the NA and matrix proteins, standardized by NA activity and administered intranasally, and were then challenged with a lethal dose of HPAI H5N1 virus. Mice previously infected with H1N1pdm09 survived H5N1 challenge with no detectable virus or respiratory tract pathology on day 4. Mice immunized with H5N1 or H1N1pdm09 NA VLPs were also fully protected from death, with a 100-fold and 10-fold reduction in infectious virus, respectively, and reduced pathology in the lungs. Human influenza vaccines that elicit not only HA, but also NA immunity may provide enhanced protection against the emergence of seasonal and pandemic viruses.     

Mycobacterium bovis BCG vaccine fails to protect protein-deficient guinea pigs against respiratory challenge with virulent Mycobacterium tuberculosis.

Specific-pathogen-free Hartley guinea pigs were maintained on isocaloric-purified diets either adequate (30%) or moderately deficient (10%) in protein. Half of each diet group was vaccinated with viable Mycobacterium bovis BCG. Six weeks later, all animals were challenged by the respiratory route with virulent Mycobacterium tuberculosis H37Rv. At intervals of 1, 2, and 3 weeks postchallenge, guinea pigs from each diet and vaccination group were skin tested with tuberculin and sacrificed. Protein deficiency resulted in loss of tuberculin hypersensitivity. Vaccination with M. bovis BCG protected control animals, as determined by significant reductions in the number of M. tuberculosis H37Rv organisms recovered from lungs, spleen, and bronchotracheal lymph nodes 2 and 3 weeks postchallenge. Based upon the same criteria, the degree of protection afforded protein-deficient animals by M. bovis BCG vaccine ranged from partial (spleen and lymph nodes) to none at all (lungs). Approximately the same numbers of tubercle bacilli were recovered from nonvaccinated guinea pigs in both diet groups. Protein deficiency appears to impair M. bovis BCG-induced immunity while not affecting primary pulmonary infection with virulent M. tuberculosis.     

Protective Immunity Conferred by the C-Terminal Fragment of Recombinant Pasteurella multocida Toxin

Pasteurella multocida serogroup D, producing P. multocida toxin (PMT), is a causative pathogen of progressive atrophic rhinitis (PAR) in swine. To evaluate the protective immunity and vaccination efficacy of the truncated form of PMT, a C-terminal form of recombinant PMT (designated PMT2.3; amino acid residues 505 to 1285 of PMT) was expressed in an Escherichia coli expression system, and the humoral and cellular immune responses to PMT2.3 were investigated. PMT2.3 vaccination in mice led to high levels of the anti-PMT antibody with a high neutralizing antibody titer. PMT2.3 also induced a cellular immune response to PMT, as demonstrated by the lymphocyte proliferation assay. Furthermore, strong protection against a homologous challenge with P. multocida was also observed in mice vaccinated with PMT2.3. In PMT2.3 vaccination in swine, high levels of serum antibody titers were observed in offspring from sows vaccinated with PMT2.3. Offspring from sows vaccinated with PMT2.3 or toxoid showed a good growth performance as depicted by mean body weight at the time of sacrifice, as well as in average daily gain in the postweaning period. Low levels of pathological lesions in turbinate atrophy and pneumonia were also observed in these offspring. Therefore, we consider PMT2.3-in the truncated and nontoxic recombinant PMT form-to be an attractive candidate for a subunit vaccine against PAR induced by P. multocida infection.     

Keeping the memory of influenza viruses

Protection against pathogens is mediated by both humoral responses (neutralizing antibodies) and cellular immunity, both CD4+ and CD8+ cells. In the case of influenza viruses, circulating strains contain both variable and conserved T and B cell epitopes that are challenged after vaccination and/or infection. During infection, the role of T cells is to prevent viral dissemination in the organism by killing the infected cells and helping B cell antibody production to neutralize the virus. The threat of influenza virus increases the preparedness of protective immunity to pandemic and seasonal infection by vaccination. Several questions remain that need to be further addressed for the future development of innovative and rapidly efficient vaccines strategies. Firstly, what are the correlates of long-term protection (antibodies and/or T cells) against variant strains of influenza? How does the individual factors (age, natural immunity, vaccination and/or infection history) influence the generation and maintenance of memory cells? What are the factors allowing the maintenance of immune memory (regular contact with the pathogen or re-vaccination)? Secondly, what is the nature and quality (function / phenotype / location) of memory B and T cells? Finally, is it necessary to induce and maintain immunological memory against conserved proteins and/or to re-vaccinate against viral variants? What would be the consequences of repeated vaccination? These questions remain a subject of debate that will be further discussed. Since immunological memory is the cornerstone of vaccination, it is essential that we have a better understanding of its generation and maintenance over time as well as its contribution to recall responses during pandemics or after vaccination.