Protection against influenza virus infection of mice fed Bifidobacterium breve YIT4064

Mice fed Bifidobacterium breve YIT4064 and immunized orally with influenza virus were more strongly protected against influenza virus infection of the lower respiratory tract than ones immunized with influenza virus only. The number of mice with enhanced anti-influenza virus immunoglobulin G (IgG) in serum upon oral administration of B. breve YIT4064 and oral immunization with influenza virus was significantly greater than that upon oral immunization with influenza virus only. These findings demonstrated that the oral administration of B. breve YIT4064 increased anti-influenza virus IgG antibodies in serum and protected against influenza virus infection. The oral administration of B. breve YIT4064 may enhance antigen-specific IgG against various pathogenic antigens taken orally and induce protection against various virus infections.     

Reduction of Influenza Virus Titer and Protection against Influenza Virus Infection in Infant Mice Fed Lactobacillus casei Shirota

We investigated whether oral administration of Lactobacillus casei strain Shirota to neonatal and infant mice ameliorates influenza virus (IFV) infection in the upper respiratory tract and protects against influenza infection. In a model of upper respiratory IFV infection, the titer of virus in the nasal washings of infant mice administered L. casei Shirota (L. casei Shirota group) was significantly (P < 0.05) lower than that in infant mice administered saline (control group) (10^2.48 ± 10^0.31 and 10^2.78 ± 10^0.4, respectively). Further, the survival rate of the L. casei Shirota group was significantly (P < 0.05) higher than that of the control group (14.3 versus 40.0%). One day after infection, pulmonary NK cell activity and interleukin-12 production by mediastinal lymph node cells of mice in the L. casei Shirota group were significantly greater than those of mice in the control group. These findings suggest that oral administration of L. casei Shirota activates the immature immune system of neonatal and infant mice and protects against IFV infection. Therefore, oral administration of L. casei Shirota may accelerate the innate immune response of the respiratory tract and protect against various respiratory infections in neonates, infants, and children, a high risk group for viral and bacterial infections.     

Augmentation of anti-influenza virus hemagglutinin antibody production by Peyer''s patch cells with Bifidobacterium breve YIT4064.

Bifidobacterium breve YIT4064 was tested an an adjuvant for oral influenza vaccine by the murine Peyer's patch cell culture method. The organism augmented production of anti-influenza virus hemagglutinin immunoglobulin A antibody by Peyer's patch cells in response to addition of hemagglutinin. These antibodies may be disseminated to the respiratory mucosal tissue and prevent influenza virus infection.     

Efficacy of Influenza Haemagglutinin and Nucleoprotein as Protective Antigens against Influenza Virus Infection in Mice

Influenza nucleoprotein (NP)-specific cytotoxic T lymphocytes (CTL) stimulated by immunization of mice with VV-PR8-NP6, a recombinant vaccinia virus expressing A/PR/8/34 NP, did not protect mice against challenge with A/PR/8/34 4 days later. Neither were secondary NP-specific CTL stimulated by reimmunization able to protect mice. These results contrast with the ability of transferred, in vitro-cultured and stimulated, NP-specific CTL to protect recipient mice from challenge with A/PR/8/34. Immunization of mice with a recombinant vaccinia virus expressing A/PR/8/34 HA protected mice challenged 4 days later, either via the small amount of antibody already present, or via HA-specific CTL that would have to be more efficient than NP-specific CTL in either trafficking to the infected lung or in effector function.     

Protection against Influenza Virus Encephalitis by Adoptive Lymphocyte Transfer

CD8+ cytotoxic T lymphocytes (CTL) have an established role in anti-viral immunity, but whether CTL function efficiently in the brain remains unclear. In particular, virus-infected neurons, which express only low levels of MHC class I antigens and are resistant to the induction of apoptosis, could constitute a relatively intractable CTL target. We have used immune lymphocytes adoptively transferred into the CSF to protect naive mice against an intracerebral infection with influenza A/WSN, a virus that infects neurons in the brain parenchyma and causes a lethal encephalitis. Afterin vitrorestimulation, heterotypically immune spleen cells protected against A/WSN encephalitis in an H-2-restricted, CD8-dependent, CD4-independent manner. Adoptively transferred CTL clones were also protective. Homotypically immune spleen cells additionally mediated CD8-independent, H-2-unrestricted protection, probably due to the generation of A/WSN-specific plasma cells from memory B cells duringin vitrorestimulation. Thus afterin vitrorestimulation, either CTL or B cells adoptively transferred into the CSF protected against an acutely lethal intracerebral virus infection.     

Recombinant Vaccine Vector-Induced Protection of Athymic, Nude Mice from Influenza A Virus Infection. Analysis of Protective Mechanisms

Athymic, nude mice, which normally succumb to virus infection, can resolve infection with recombinant vaccinia virus (rVV) engineered to express IL-2. We have demonstrated that interferon-gamma (IFN-gamma) produced by natural killer (NK) cells and other immunocytes in response to the virus-encoded interleukin-2 (IL-2) is crucial to recovery. Here, we extend this work to show that nude mice, when primed intravenously with rVV co-expressing both IL-2 and an influenza virus haemagglutinin (HA) gene, are also protected following challenge with a lethal dose of homologous influenza virus. A substantial increase in the number of influenza virus-reactive antibody-secreting cells producing antibody of the IgM isotype, but not of the IgG or IgA isotypes, was found in spleens and lungs of the protected mice. Treatment with monoclonal antibodies to IFN-gamma or to the NK marker, as GM1, at challenge and thereafter, led to their death however, though the specific IgM antibody response was unaffected. These data suggest that both specific antibody and non-specific antiviral reactivity are important elements of the protective response and show that this immunization strategy may be used to protect severely immunocompromised individuals.     

Effects of Low- and High-Passage Influenza Virus Infection in Normal and Nude Mice

A human isolate of type A Hong Kong influenza virus (H3N2) was adapted to mice by serial passage. Lung homogenates from mice who received low passage levels contained about the same quantity of virus (10^6.2−6.95 50% tissue culture infective doses/ml) as those from mice who received high passage levels (10^5.95−6.45 50% tissue culture infective doses/ml); however, death occurred only in animals given high-passage virus. Passage 3 (P3) and passage 9 (P9) viruses were selected as representative of low-passage and high-passage viruses, respectively. Although minimal differences were detected in infectivity for rhesus monkey kidney tissue cultures and mice, P9 virus was at least 10,000 times more lethal for mice (mean lethal dose = 10^4.2). Infection with P3 virus was accompanied by minimal bronchitis and bronchiolitis only, whereas P9-infected animals exhibited marked bronchitis, bronchiolitis, and pneumonia. Striking thymic cortical atrophy was also demonstrable in the P9-infected animals and, although virus was more commonly recovered from thymuses from these animals, immunofluorescent studies revealed only a few cells containing influenza virus antigens. To further explore the participation of thymus-derived lymphocytes in influenza, athymic nude mice and furred immunocompetent littermates were given 500 50% mouse infectious doses of P9 virus. Nude mice exhibited an increased survival time and, in contrast to the extensive lung pathology seen in furred littermates, manifested minimal cellular infiltration and no tissue destruction in lungs. Brains from nude mice exhibited encephalomalacia with lymphocytic perivascular cuffing, which was not seen in furred animals. Virus was recovered from brains of 6 of 13 nude mice and 1 of 10 furred animals. The contrasting models suggest that thymus-dependent cells play a significant role in the inflammatory response to influenza virus infection and should prove useful for probing host-virus interactions which characterize influenza virus virulence.     

Intranasal Delivery of an IgA Monoclonal Antibody Effective against Sublethal H5N1 Influenza Virus Infection in Mice

Highly pathogenic avian H5N1 influenza viruses are endemic in poultry in Asia and pose a pandemic threat to humans. Since the deployment of vaccines against a pandemic strain may take several months, adequate antiviral alternatives are needed to minimize the effects and the spread of the disease. Passive immunotherapy is regarded as a viable alternative. Here, we show the development of an IgA monoclonal antibody (DPJY01 MAb) specific to H5 hemagglutinin. The DPJY01 MAb showed a broad hemagglutination inhibition (HI) profile against Asian H5N1 viruses of clades 0, 1.0, 2.1, 2.2, and 2.3 and also against H5 wild bird influenza viruses of the North American and Eurasian lineages. DPJY01 MAb displayed also high neutralization activity in vitro and in vivo. In mice, DPJY01 MAb provided protection via a single dose administered intranasally before or after inoculation with a sublethal dose of H5N1 viruses of clades 1.0 and 2.2. Pretreatment with 50 mg of DPJY01 MAb kg of body weight at either 24, 48, or 72 h before highly pathogenic H5N1 virus (A/Vietnam/1203/2004 [H5N1]) inoculation resulted in complete protection. Treatment with 50 mg/kg at either at 24, 48, or 72 h after H5N1 inoculation provided 100%, 80%, and 60% protection, respectively. These studies highlight the potential use of DPJY01 MAb as an intranasal antiviral treatment for H5N1 influenza virus infections.Influenza type A viruses are negative-sense segmented RNA viruses that belong to the family Orthomyxoviridae (11). They are further subdivided into subtypes based on the antigenic properties of the two surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA). Among these subtypes, the highly pathogenic avian H5N1 influenza viruses have been intensively studied since the first report of lethal human infections in 1997 (36). H5N1 viruses continue to circulate in poultry in Asia and occasionally are transmitted from birds to humans, posing a potential pandemic threat (1). As of 6 April 2010, the World Health Organization (WHO) had reported 493 human infections with 292 deaths, a fatality rate exceeding 60%. These strains have shown significant evolutionary changes and are currently divided into 10 HA clades (36). Among these clades, clade 2 is further classified into five subclades (2.1 to 2.5), and within each subclade there are several lineages (35). Clade 2.1 is predominant in Indonesia, the country in which H5N1 has become endemic and in which the highest number of human infections and associated fatalities have been reported. In Indonesia, of the 163 cases confirmed to date by the WHO, 135 have been fatal. The latest human infections with H5N1 viruses have been reported in Egypt, where viruses from clade 2.2.1 are endemic. In Egypt since 2006, H5N1 viruses have been identified as the causative agent in 109 human infections with 34 deaths according to the WHO. More importantly, some of these strains have developed resistance to available antiviral drugs (17, 21). For example, most clade 1 H5N1 viruses are resistant to adamantanes (10), and oseltamivir-resistant H5N1 viruses with neuraminidase mutations (H274Y and N294S) have been also identified in infected patients during or after treatment (7, 12). These limitations and others, such as the poor immunogenicity of H5N1 vaccines (3, 16, 26, 31), call for the development of alternative intervention strategies.Several groups have reported the development of monoclonal antibodies (MAbs) against the HA of influenza viruses, particularly against the H1, H3, and H5 subtypes (9, 14, 38). Some of these MAbs have broad subtype cross-reactions (38). Human and mouse monoclonal antibodies against H5 HA have been shown to provide protection against lethal infection in a mouse model (4, 20, 24). These anti-H5 MAbs are usually of the IgG1 or IgG2a subtypes and are administered by parenteral routes. Retrospective studies have suggested that those patients with influenza pneumonia during the 1918 Spanish influenza pandemic who received influenza convalescent-phase human blood products may have experienced a reduction in the risk of death (15), and H5N1-infected patients treated with convalescent H5N1 plasma recovered from the infection (39). Therefore, passive antibody immunotherapy is an attractive and potentially efficient alternative for the treatment of H5N1 infections. To our knowledge, intranasal administration of antibodies against H5N1 has not been reported. Although intranasal administration of drugs depends largely on the health status of the patient, it does represent an alternative intervention strategy. Intranasal administration of antibodies would allow the antibodies to directly reach their target in the respiratory track, which is the major site for influenza virus replication in humans and other mammals (29, 33). IgA-mediated neutralization monoclonal antibody therapy against H5N1 has not been reported, and only a few IgA MAbs against A/Puerto Rico/8/34 (H1N1) have been reported to show antiviral activity when given intravenously (2). In this study, we generated an IgA monoclonal antibody (DPJY01) with a broad HI profile and high neutralization activity against the H5N1 virus in vitro and in vivo. Remarkably, DPJY01 provided protection against sublethal H5N1 infection after a single dose through intranasal administration.     

Vaccine Protection of Leukopenic Mice against Staphylococcus aureus Bloodstream Infection

The risk for Staphylococcus aureus bloodstream infection (BSI) is increased in immunocompromised individuals, including patients with hematologic malignancy and/or chemotherapy. Due to the emergence of antibiotic-resistant strains, designated methicillin-resistant S. aureus (MRSA), staphylococcal BSI in cancer patients is associated with high mortality; however, neither a protective vaccine nor pathogen-specific immunotherapy is currently available. Here, we modeled staphylococcal BSI in leukopenic CD-1 mice that had been treated with cyclophosphamide, a drug for leukemia and lymphoma patients. Cyclophosphamide-treated mice were highly sensitive to S. aureus BSI and developed infectious lesions lacking immune cell infiltrates. Virulence factors of S. aureus that are key for disease establishment in immunocompetent hosts—α-hemolysin (Hla), iron-regulated surface determinants (IsdA and IsdB), coagulase (Coa), and von Willebrand factor binding protein (vWbp)—are dispensable for the pathogenesis of BSI in leukopenic mice. In contrast, sortase A mutants, which cannot assemble surface proteins, display delayed time to death and increased survival in this model. A vaccine with four surface antigens (ClfA, FnBPB, SdrD, and SpA_KKAA), which was identified by genetic vaccinology using sortase A mutants, raised antigen-specific immune responses that protected leukopenic mice against staphylococcal BSI.     

应用McAb和免疫血清对不同HFRS病毒株感染乳鼠保护作用的比较

HFRS病毒陈茱、76-118株和R22株100LD_(50)分别感染新生乳鼠。感染后24h,经腹腔分别接种McAb(3D8、3G1、8F8、8G3和8G2)和免疫血清(陈株、76-118株和R22株),结果发现,这5株McAb对陈林和76-118株感染乳鼠100％保护,而对R22株感染乳鼠只有McAb8F8有25％保护,而其佘McAb均无保护。免疫血清的保护实验也表明,陈株和76-118株可以交互保护。上述结果提示,陈株与76-118株保护性抗原较一致,但R22株与前两株差别较大。     

Adeno-Associated Virus 9-Mediated Airway Expression of Antibody Protects Old and Immunodeficient Mice against Influenza Virus

Influenza causes serious and sometimes fatal disease in individuals at risk due to advanced age or immunodeficiencies. Despite progress in the development of seasonal influenza vaccines, vaccine efficacy in elderly and immunocompromised individuals remains low. We recently developed a passive immunization strategy using an adeno-associated virus (AAV) vector to deliver a neutralizing anti-influenza antibody at the site of infection, the nasal airways. Here we show that young, old, and immunodeficient (severe combined immunodeficient [SCID]) mice that were treated intranasally with AAV9 vector expressing a modified version of the broadly neutralizing anti-influenza antibody FI6 were protected and exhibited no signs of disease following an intranasal challenge with the mouse-adapted H1N1 influenza strain A/Puerto Rico/8/1934(H1N1) (PR8) (Mt. Sinai strain). Nonvaccinated mice succumbed to the PR8 challenge due to severe weight loss. We propose that airway-directed AAV9 passive immunization against airborne infectious agents may be beneficial in elderly and immunocompromised patients, for whom there still exists an unmet need for effective vaccination against influenza.     

Interferon-Inducing Polycarboxylates: Mechanism of Protection Against Vaccinia Virus Infection in Mice

The present study was undertaken to examine possible correlations between long-term protection of mice treated with polycarboxylates and infected with vaccinia virus, and the presence of subdetectable amounts of interferon in the tissues, as determined by tissue or organ resistance to replication of viruses. After a single dose of polycarboxylate, splenic resistance to virus replication could be detected. It persisted for 7 to 14 days, but no attempt was made to prove that it was due to subdetectable amounts of interferon. Whole-animal protection lasted longer than splenic resistance. Moreover, when different polycarboxylates and different virus strains were used, patterns of early protection were not correlated with those of splenic resistance. These data, as others presented earlier, suggest that, in addition to interferon, other antiviral mechanisms are stimulated by polycarboxylates.     

Augmentation of Cellular Immunity and Reduction of Influenza Virus Titer in Aged Mice Fed Lactobacillus casei Strain Shirota

We investigated whether oral administration of Lactobacillus casei strain Shirota activates the cellular immune system and ameliorates influenza virus (IFV) titer in the nasal site in upper respiratory IFV infection by using aged mice. Natural killer activity of splenocytes and lung cells of aged mice fed an L. casei strain Shirota diet (L.casei strain Shirota group) was significantly (P < 0.01 and P < 0.05) increased compared to those fed a control diet (control group). The increases were 1.5- and 2.5-fold, respectively. In aged mice fed an XL.casei strain Shirota diet, potent induction of gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α), which play a very important role in excluding IFV, was evident in nasal lymphocytes. IFN-γ and TNF-α production increased 12- and 3.5-fold, respectively. In this model of upper respiratory IFV infection, the titer of IFV in the nasal washings of aged mice fed an L.casei strain Shirota diet was significantly (P < 0.05) lower than that in aged mice fed a control diet (10^{1.6 ± 0.6} and 10^{2.2 ± 0.5}, respectively). These findings suggest that oral administration of L.casei strain Shirota activates not only systemic cellular immunity but also local cellular immunity and that it ameliorates IFV infection.     

Prophylaxis and Treatment of Influenza Virus Infection

Influenza virus infections remain an important cause of morbidity and mortality. Furthermore, a recurrence of pandemic influenza remains a real possibility. There are now effective ways to both prevent and treat influenza. Prevention of infection is most effectively accomplished by vaccination. Vaccination with the inactivated, intramuscular influenza vaccine has been clearly demonstrated to reduce serious morbidity and mortality associated with influenza infection, especially in groups of patients at high risk (e.g. the elderly). However, the inactivated, intramuscular vaccine does not strongly induce cell-mediated or mucosal immune responses, and protection induced by the vaccine is highly strain specific. Live, attenuated influenza vaccines administered intranasally have been studied in clinical trials and shown to elicit stronger mucosal and cell-mediated immune responses. Live, attenuated vaccines appear to be more effective for inducing protective immunity in children or the elderly than inactivated, intramuscular vaccines. Additionally, novel vaccine methodologies employing conserved com-ponents of influenza virus or viral DNA are being developed. Preclinical studies suggest that these approaches may lead to methods of vaccination that could induce immunity against diverse strains or subtypes of influenza. Because of the limitations of vaccination, antiviral therapy continues to play an important role in the control of influenza. Two major classes of antivirais have demonstrated ability to prevent or treat influenza in clinical trials: the adaman-tanes and the neuraminidase inhibitors. The adamantanes (amantadine and rimantadine) have been in use for many years. They inhibit viral uncoating by blocking the proton channel activity of the influenza A viral M2 protein. Limitations of the adamantanes include lack of activity against influenza B, toxicity (especially in the elderly), and the rapid development of resistance. The neuraminidase inhibitors were designed to interfere with the conserved sialic acid binding site of the viral neuraminidase and act against both influenza A and B with a high degree of specificity when administered by the oral (oseltamivir) or inhaled (zanamivir) route. The neuraminidase inhibitors have relatively low toxicity, and viral resistance to these inhibitors appears to be uncommon. Additional novel antivirals that target other phases of the life cycle of influenza are in preclinical development. For example, recombinant collectins inhibit replication of influenza by binding to the viral haemagglutinin as well as altering phagocyte responses to the virus. Recombinant techniques have been used for generation of antiviral proteins (e.g. modified collectins) or oligonucleotides. Greater understanding of the biology of influenza viruses has already resulted in significant advances in the management of this important pathogen. Further advances in vaccination and antiviral therapy of influenza should remain a high priority.     

The Generation of 'Cytotoxic' Macrophages in Mice during Infection with Influenza A or Sendai Virus

Injection of infectious but not of non-infections influenza A virus or of infectious or non-infectious Sendai virus intraperitoneally into mice induces the generation of plastic-adherent cells that arc able to effect release of ⁵¹Cr from labelled virus-infected target cells but not from labelled, uninfcctcd cells. Their activity is greatly diminished by exposure to silica or carrageenan but not by anti-Thy I antibody and complement treatment. Similarly, the activity of the cell preparation cannot be explained by contamination with natural killer or 'K' cells. Thus, the effector cells were identified as macrophages and for convenience are called 'cytotoxic macrophages'. The maximum cytotoxic activity was recovered from the peritoneal cavity 5 days after virus injection and declined thereafter. Although the effector cells are cross-reactive in that cells activated by an influenza A strain virus lyse target cells infected with the same or other A strain viruses or with Sendai virus, there is preferential lysis of cells infected with the homologous virus. The action of the effector cells is not H-2-restrictcd. Preliminary experiments showed that similar effector cells can be recovered from the lungs of mice 5 days after intranasal inoculation of infectious influenza virus, so they may contribute to the host control of the disease.     

Histology and Ultrastructure of Metaplasia of Alveolar Epithelium Following Infection of Mice and Hamsters with Influenza Virus

Mice and hamsters were infected with the NWS strain of influenza virus and metaplastic changes which developed in the lungs during the healing phase were studied by histology and electron microscopy. Transformation of alveolar epithelium occurred in many animals, producing alveolar epithelialization. This was due to replacement of the normal alveolar epithelium by ciliated columnar and cuboidal cells of bronchiolar type. Squamous changes also developed in healing lungs during the 11-22 day period after infection. Since these lesions regressed later and the cells did not metastasize they were considered to be metaplastic rather than neoplastic in nature.     

Isotype Switching Increases Efficacy of Antibody Protection against Cryptococcus neoformans Infection in Mice

The isotype and epitope specificities of antibodies both contribute to the efficacy of antibodies that mediate immunity to Cryptococcus neoformans, but the relationship between these properties is only partially understood. In this study, we analyzed the efficacy of protection of two sets of immunoglobulin G (IgG) isotype switch variants from two IgG3 monoclonal antibodies (MAbs) which are either not protective or disease enhancing, depending on the mouse model used. The two IgG3 MAbs 3E5 and 4H3 have different epitope specificities. Protection experiments were done with A/JCr mice infected intravenously with C. neoformans and administered with 3E5 IgG3 and its IgG1, IgG2a, and IgG2b switch variants. These experiments revealed that IgG1, IgG2b, and IgG2a were each more effective than IgG3. For 4H3 IgG3 and its IgG1 and IgG2b switch variants, the relative efficacy was IgG2b > IgG1 >> IgG3. The combination of 3E5 IgG3 and 4H3 IgG3 was more deleterious than either IgG3 alone. All IgG isotypes were opsonic for mouse bronchoalveolar cells, with the relative efficacy being IgG2b > IgG2a > IgG1 > IgG3. These results (i) confirm that a nonprotective IgG3 MAb can be converted to a protective MAb by isotype switching, (ii) indicate that the efficacy of protection of an IgG1 MAb can be increased by isotype switching to another subclass, (iii) show that protective and nonprotective IgG MAbs are opsonic, and (iv) provide additional evidence for the concept that the efficacy of the antibody response to C. neoformans is dependent on the type of MAb elicited.Cryptococcus neoformans is a fungus which is a frequent cause of life-threatening meningoencephalitis in patients with impaired immunity (22, 25). Cryptococcosis has been reported to occur in 6 to 8% of patients with AIDS (7). In immunocompromised individuals, C. neoformans infections are often incurable with conventional antifungal agents, and these patients frequently require lifelong therapy (45). The difficulties involved in the management of cryptococcosis in immunocompromised individuals have led to a reexamination of the potential of antibody-mediated immunity for prevention and therapy of cryptococcal infections. A polysaccharide-tetanus toxoid (TT) conjugate vaccine which is highly immunogenic and can elicit protective antibodies in mice has been made (3, 8, 9). In addition, several monoclonal antibodies (MAbs) have been shown to modify the course of infection in mice, and these may be useful in therapy of human infection (12, 14, 28, 42, 43).Cell-mediated immunity is generally acknowledged to provide important host defense against C. neoformans infection (4, 20, 26, 31, 42). In contrast, the role of antibody-mediated immunity in host resistance is less certain (2), but there is considerable evidence that administration of some MAbs can modify the course of infection in mice (8, 12, 14, 16, 28, 33). C. neoformans is unusual among fungal pathogens in that it has a polysaccharide capsule composed primarily of glucuronoxylomannan (GXM) (6), which is important for virulence (5). The capsular polysaccharide has been shown to produce a variety of deleterious effects including inhibition of phagocytosis (21), interference with antigen presentation (39), shedding of adhesion molecules (11), inhibition of leukocyte migration (10), and alterations in cytokine production by host effector cells (24, 40, 41). Antibodies to the C. neoformans capsular polysaccharide may contribute to host defense through multiple effects including enhanced opsonization (13, 18, 23, 30, 44), clearance of polysaccharide antigen (15), promotion of granuloma formation (14), and release of oxygen- and nitrogen-derived oxidants (27, 38).In previous studies, we demonstrated that immunoglobulin G3 (IgG3) MAbs are not protective in various mouse models of cryptococcal infection (32, 42). When one of these nonprotective IgG3 MAbs was switched to IgG1, the IgG1 significantly prolonged animal survival (32, 42). In the present study, we analyzed two families of IgG switch variants generated in vitro from two nonprotective IgG3 MAbs with different epitope specificities. We found that MAbs with different isotypes have different protective efficacies and that switching of nonprotective IgG3 MAbs to IgG1, IgG2b, and IgG2a significantly increased antibody protective efficacy. These studies demonstrate a complex relationship among efficacy of antibody protection, epitope specificity, and isotype.