Mechanisms of vaccine-induced protective immunity against Coxiella burnetii infection in BALB/c mice

To elucidate the mechanisms of vaccine-induced protective immunity against Coxiella burnetii infection, we compared the protective efficacy and immunogenicity between formalin-inactivated phase I vaccine (PI-V) and phase II vaccine (PII-V) in BALB/c mice. PI-V generated significant protection while PII-V did not confer measurable protection. Analysis of cytokine and subclass Ab responses indicated that both PI-V and PII-V were able to induce a Th1-dominant immune response but did not identify the component of host response that distinguished their ability to induce protective immunity. Interestingly, immunoblot analysis identified a difference between PI-V and PII-V vaccinates in antigenic recognition by specific Ab isotypes. The observation that PI-LPS elicited significant protection but PII-LPS did not confer measurable protection suggests PI-LPS may play a key role in PI-V-induced protection. Adoptive transfer of either immune sera or splenocytes mediated significant protection in naive BALB/c mice, supporting the notion that both humoral and cellular immunity are important for development of protective immunity. However, the evidence that immune sera and B cells were unable to control infection while T cells conferred significant protection in SCID mice supports the hypothesis that T cell-mediated immunity is critical for host defense against C. burnetii infection. This report presents novel evidence to highlight the importance of PI-LPS and Abs in protective immunity and has important implications for the design of new generation vaccines against Q fever.     

A cryptococcal capsular polysaccharide mimotope prolongs the survival of mice with Cryptococcus neoformans infection

Defined Abs to the Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM) have been shown to be protective against experimental cryptococcosis. This suggests that if a vaccine could induce similar Abs it might protect against infection. However, the potential use of a GXM-based vaccine has been limited by evidence that GXM is a poor immunogen that can induce nonprotective and deleterious, as well as protective, Abs, and that the nature of GXM oligosaccharide epitopes that can elicit a protective response is unknown. In this study, we investigated whether a peptide surrogate for a GXM epitope could induce an Ab response to GXM in mice. The immunogenicity of peptide-protein conjugates produced by linking a peptide mimetic of GXM, P13, to either BSA, P13-BSA, or tetanus toxoid, P13-tetanus toxoid, was examined in BALB/c and CBA/n mice that received four s.c. injections of the conjugates at 14- to 30-day intervals. All mice immunized with conjugate produced IgM and IgG to P13 and GXM. Challenge of conjugate-immunized mice with C. neoformans revealed longer survival and lower serum GXM levels than control mice. These results indicate that 1) P13 is a GXM mimotope and 2) that it induced a protective response against C. neoformans in mice. P13 is the first reported mimotope of a C. neoformans Ag. Therefore, the P13 conjugates are vaccine candidates for C. neoformans and their efficacy in this study suggests that peptide mimotopes selected by protective Abs deserve further consideration as vaccine candidates for encapsulated pathogens.     

An outline of the role of anti-Candida antibodies within the context of passive immunization and protection from candidiasis

The role played by antibodies (Abs) in the anticandidal defense has long been a matter of controversy, mostly due to the past inability to clearly define antigen specificity, the relationship between the type of immune response within the different settings of experimental and human candidiasis and, last but not least, a misunderstanding about the role of T helper cell in cell-mediated versus the humoral immunity. Contributory was also the lack of precise identification of virulence traits of the fungus which are the best candidates for a protective Ab response. In recent years, an impressive amount of experimental evidence, and also some clinical proof, have been generated which assign to Abs of defined specificity an important role in the anticandidal defense both at systemic and mucosal sites. Paradigmatic among them, Abs against defined virulence factors such as adhesins or aspartyl-proteinase enzymes, or against critical viability molecules such as beta-glucan, have been detected or generated which hold great promise for immunotherapeutic interventions in humans.     

Mouse genetic background is a major determinant of isotype-related differences for antibody-mediated protective efficacy against Cryptococcus neoformans

The protective efficacy of mAbs to Cryptococcus neoformans glucuronoxylomannan depends on Ab isotype. Previous studies in A/JCr and C57BL/6J mice showed relative protective efficacy of IgG1, IgG2a > IgG3. However, we now report that in C57BL/6J x 129/Sv mice, IgG3 is protective while IgG1 is not protective, with neither isotype being protective in 129/Sv mice. IgG1, IgG2a, and IgG3 had different effects on IFN-gamma expression in infected C57BL/6J x 129/Sv mice. IgG1-treated C57BL/6J x 129/Sv mice had significantly more pulmonary eosinophilia than IgG2a- and IgG3-treated C57BL/6J x 129/Sv mice. C. neoformans infection and Ab administration had different effects on FcgammaRI, FcgammaRII, and FcgammaRIII expression in C57BL/6J, 129/Sv, and C57BL/6J x 129/Sv mice. Our results indicate that the relative efficacy of Ab isotype function against C. neoformans is a function of the genetic background of the host and that IgG3-mediated protection in C57BL/6J x 129/Sv mice was associated with lower levels of IFN-gamma and fewer pulmonary eosinophils. The dependence of isotype efficacy on host genetics underscores a previously unsuspected complex relationship between the cellular and humoral arms of the adaptive immune response.     

Unexpected diversity in the fine specificity of monoclonal antibodies that use the same V region gene to glucuronoxylomannan of Cryptococcus neoformans

Most mAbs to the capsular polysaccharide glucuronoxylomannan (GXM) of Cryptococcus neoformans are generated from the same VH and VL gene families. Prior Ab studies have assessed protective efficacy, Id structure and binding to capsular polysaccharides, and peptide mimetics. These data have been interpreted as indicating that most mAbs to GXM have the same specificity. A new approach to Ab specificity analysis was investigated that uses genetic manipulation to generate C. neoformans variants with structurally different capsules. C. neoformans mutants expressing GXM with defective O-acetylation were isolated and complemented by the C. neoformans gene CAS1, which is necessary for the O-acetylation of GXM. The mAbs exhibited differences in their binding to the GXM from these mutant strains, indicating previously unsuspected differences in specificity. Analysis of three closely related IgMs revealed that one (mAb 12A1) bound to an epitope that did not require O-acetylation, another (mAb 21D2) was inhibited by O-acetylation, and the third (mAb 13F1) recognized an O-acetylation-dependent conformational epitope. Furthermore, an IgG Ab (mAb 18B7) in clinical development retained binding to de-O-acetylated polysaccharide; however, greater binding was observed to O-acetylated GXM. Our findings suggest that microbial genetic techniques can provide a new approach for epitope mapping of polysaccharide-binding Abs and suggest that this method may applicable for studying the antigenic complexity of polysaccharide Ags in other capsulated microorganisms.     

Cryptococcus neoformans is resistant to surfactant protein A mediated host defense mechanisms

Initiation of a protective immune response to infection by the pathogenic fungus Cryptococcus neoformans is mediated in part by host factors that promote interactions between immune cells and C. neoformans yeast. Surfactant protein A (SP-A) contributes positively to pulmonary host defenses against a variety of bacteria, viruses, and fungi in part by promoting the recognition and phagocytosis of these pathogens by alveolar macrophages. In the present study we investigated the role of SP-A as a mediator of host defense against the pulmonary pathogen, C. neoformans. Previous studies have shown that SP-A binds to acapsular and minimally encapsulated strains of C. neoformans. Using in vitro binding assays we confirmed that SP-A does not directly bind to a fully encapsulated strain of C. neoformans (H99). However, we observed that when C. neoformans was incubated in bronchoalveolar fluid, SP-A binding was detected, suggesting that another alveolar host factor may enable SP-A binding. Indeed, we discovered that SP-A binds encapsulated C. neoformans via a previously unknown IgG dependent mechanism. The consequence of this interaction was the inhibition of IgG-mediated phagocytosis of C. neoformans by alveolar macrophages. Therefore, to assess the contribution of SP-A to the pulmonary host defenses we compared in vivo infections using SP-A null mice (SP-A-/-) and wild-type mice in an intranasal infection model. We found that the immune response assessed by cellular counts, TNFalpha cytokine production, and fungal burden in lungs and bronchoalveolar lavage fluids during early stages of infection were equivalent. Furthermore, the survival outcome of C. neoformans infection was equivalent in SP-A-/- and wild-type mice. Our results suggest that unlike a variety of bacteria, viruses, and other fungi, progression of disease with an inhalational challenge of C. neoformans does not appear to be negatively or positively affected by SP-A mediated mechanisms of pulmonary host defense.     

Induced humoral immunity and vaccination against major human fungal pathogens

Protection against fungal pathogens can theoretically be elicited by vaccines that stimulate humoral or cellular immunity, or both. There is conclusive evidence that humoral immunity can modify the course of infection against certain pathogenic fungi such as Candida albicans and Cryptococcus neoformans. However, for other fungi, such as Aspergillus fumigatus, the notion that humoral immunity contributes to host defence is unproven. Attempts to evaluate the potential efficacy of humoral immunity using immune sera are often inconclusive, whereas consistent results can be obtained with monoclonal antibodies. Protective monoclonal antibodies can be used to identify antigens that induce useful humoral responses.     

T-cell Subsets and Antifungal Host Defenses

It has been long appreciated that protective immunity against fungal pathogens is dependent on activation of cellular adaptive immune responses represented by T lymphocytes. The T-helper (Th)1/Th2 paradigm has proven to be essential for the understanding of protective adaptive host responses. Studies that have examined the significance of regulatory T cells in fungal infection, and the recent discovery of a new T-helper subset called Th17 have provided crucial information for understanding the complementary roles played by the various T-helper lymphocytes in systemic versus mucosal antifungal host defense. This review provides an overview of the role of the various T-cell subsets during fungal infections and the reciprocal regulation between the T-cell subsets contributing to the tailored host response against fungal pathogens.     

Humoral immune response to flagellin requires T cells and activation of innate immunity

Bacterial flagellin, the primary structural component of flagella, is a dominant target of humoral immunity upon infection by enteric pathogens and in Crohn's disease. To better understand how such responses may be regulated, we sought to define, in mice, basic mechanisms that regulate generation of flagellin-specific Igs. We observed that, in response to i.p. injection with flagellin, generation of flagellin-specific Ig required activation of innate immunity in that these responses were ablated in MyD88-deficient mice and that flagellin from Helicobacter pylori, which is known not to activate TLR5, also did not elicit Abs. Mice lacking alphabeta T cells (TCRbeta(null)) were completely deficient in their ability to make flagellin Abs in various contexts indicating that, in contrast to common belief, generation of flagellin-specific Ig is absolutely T cell dependent. In contrast to Ab responses to whole flagella (H serotyping), responses to flagellin monomers displayed only moderate serospecificity. Whereas neither oral nor rectal administration of flagellin elicited a strong serum Ab response, induction of colitis with dextran sodium sulfate resulted in a MyD88-dependent serum Ab response to endogenous flagellin, suggesting that, in an inflammatory milieu, TLR signaling promotes acquisition of Abs to intestinal flagellin. Thus, acquisition of a humoral immune response to flagellin requires activation of innate immunity, is T cell dependent, and can originate from flagellin in the intestinal tract in inflammatory conditions in the intestine.     

Generation of antifungal effector CD8+ T cells in the absence of CD4+ T cells during Cryptococcus neoformans infection

Immunity to the opportunistic fungus Cryptococcus neoformans is dependent on cell-mediated immunity. Individuals with defects in cellular immunity, CD4(+) T cells in particular, are susceptible to infection with this pathogen. In host defense against a number of pathogens, CD8(+) T cell responses are dependent upon CD4(+) T cell help. The goal of these studies was to determine whether CD4(+) T cells are required for the generation of antifungal CD8(+) T cell effectors during pulmonary C. neoformans infection. Using a murine intratracheal infection model, our results demonstrated that CD4(+) T cells were not required for the expansion and trafficking of CD8(+) T cells to the site of infection. CD4(+) T cells were also not required for the generation of IFN-gamma-producing CD8(+) T cell effectors in the lungs. In CD4(-) mice, depletion of CD8(+) T cells resulted in increased intracellular infection of pulmonary macrophages by C. neoformans, increasing the pulmonary burden of the infection. Neutralization of IFN-gamma in CD4(-)CD8(+) mice similarly increased macrophage infection by C. neoformans, thereby blocking the protection provided by CD8(+) T cells. Altogether, these data support the hypothesis that effector CD8(+) T cell function is independent of CD4(+) T cells and that IFN-gamma production from CD8(+) T cells plays a role in controlling C. neoformans by limiting survival of C. neoformans within macrophages.     

Stimulation of Cryptococcus neoformans isolated from skin lesion of AIDS patient matures dendritic cells and promotes HIV-1 trans-infection

Dendritic cells (DCs) play a pivotal role in host defense against invaded pathogens including fungi, while DCs are targeted by fungi for deleterious regulation of the host immune response. A few studies have reported fungal modulation of DC function in these immunocompromised AIDS patients. Cryptococcus neoformans (C. neoformans) is referred as one of the opportunistic fungi of AIDS. Here, we isolated native C. neoformans from an AIDS patient and investigated its effects on DC activation and function. Stimulation of C. neoformans matured DCs, and enhanced DC-mediated HIV-1 trans-infection; moreover, C. neoformans-stimulated DCs promoted the activation of resting T cells and provided more susceptible targets for HIV-1 infection. Microbial translocation has been proposed as the cause of systemic immune activation in chronic HIV-1 infection. Understanding the potential effects of pathogens on HIV-1-DC interactions could help elucidate viral pathogenesis and provide a new insight for against the spread of HIV.     

Antibody efficacy in murine pulmonary Cryptococcus neoformans infection: a role for nitric oxide

We investigated the pathogenesis of pulmonary Cryptococcus neoformans infection and passive Ab efficacy in mice deficient in inducible NO synthase (NOS2(-/-)) and the parental strain. Parental mice lived significantly longer than NOS2(-/-) mice after intratracheal infection, despite having a higher lung fungal burden. Administration of Ab reduced lung CFU in both NOS2(-/-) and parental mice, but prolonged survival and increased the inflammatory response only in parental mice. Ab administration was associated with increased serum nitrite and reduced polysaccharide levels in parental mice. Eosinophils were present in greater numbers in the lung of infected NOS2(-/-) mice than parental mice, irrespective of Ab administration. C. neoformans infection in NOS2(-/-) mice resulted in significantly higher levels of IFN-gamma, monocyte chemoattractant protein-1, and macrophage-inflammatory protein-1alpha than parental mice. Ab administration had different effects on infected NOS2(-/-) and parental mice with respect to IFN-gamma, monocoyte chemoattractant protein-1, and macrophage-inflammatory protein-1alpha levels. Ab administration increased lung levels of IFN-gamma in parental mice and reduced levels in NOS2(-/-) mice. The results indicate that NO is involved in the regulation of cytokine expression in response to cryptococcal pneumonia and is necessary for Ab efficacy against C. neoformans in mice. Our findings indicate a complex relationship between Ab efficacy against C. neoformans and cytokine expression, underscoring the interdependency of cellular and humoral defense mechanisms.     

Antibodies to keyhole limpet hemocyanin cross-react with an epitope on the polysaccharide capsule of Cryptococcus neoformans and other carbohydrates: implications for vaccine development

Cryptococcus neoformans causes a life-threatening meningoencephalitis in AIDS patients. Mice immunized with a glycoconjugate vaccine composed of the glucuronoxylomannan (GXM) component of the cryptococcal capsular polysaccharide conjugated to tetanus toxoid produce Abs that can be either protective or nonprotective. Because nonprotective Abs block the efficacy of protective Abs, an effective vaccine must focus the Ab response on a protective epitope. Mice immunized with peptide mimetics of GXM conjugated to keyhole limpet hemocyanin (KLH) with glutaraldehyde developed Abs to GXM. However, control peptides P315 and P24 conjugated to KLH also elicited Abs to GXM. GXM-binding Abs from mice immunized with P315-KLH were inhibited by KLH treated with glutaraldehyde (KLH-g), but not by P315. Furthermore, KLH-g inhibited binding of GXM by serum of mice immunized with GXM-TT, indicating that glutaraldehyde treatment of KLH reveals an epitope(s) that cross-reacts with GXM. Vaccination with KLH-g or unmodified KLH elicited Abs to GXM, but did not confer protection against C. neoformans, suggesting the cross-reactive epitope on KLH was not protective. This was supported by the finding that 4H3, a nonprotective mAb, cross-reacted strongly with KLH-g. Sera from mice immunized with either native KLH or KLH-g cross-reacted with several other carbohydrate Ags, many of which have been conjugated to KLH for vaccine development. This study illustrates how mAbs can be used to determine the efficacy of potential vaccines, in addition to describing the complexity of using KLH and glutaraldehyde in the development of vaccines to carbohydrate Ags.     

More is not necessarily better: prozone-like effects in passive immunization with IgG

Despite a century of study, the relationship between Ag-specific Ig concentration and protection remains poorly understood for the majority of pathogens. In certain conditions, administration of high Ab doses before challenge with an infectious agent can be less effective than smaller Ab doses, a phenomenon which is consistent with a prozone-like effect. In this study, the relationship between IgG1, IgG2a, IgG2b, and IgG3 dose, infective inocula, and protection was investigated in a mouse model of Cryptococcus neoformans infection. The activity of each IgG subclass ranged from protective to disease-enhancing depending on both the Ab dose and infective inocula used. Enhanced dissemination to the brain was observed in mice given a high IgG2a dose and a relatively low inoculum. Ab administration had immunomodulatory effects, with cytokine expression in lung, brain, and spleen varying as a function of the infective inoculum Ab dose and IgG subclass. In vitro studies did not predict or explain the mechanism of in vivo prozone-like effects, because all isotypes were opsonic and elicited NO release from macrophages. IgG2a was most efficient in inducing a macrophage oxidative burst. These results reveal that an individual Ab can be protective, nonprotective, or disease-enhancing depending on its concentration relative to a challenge inoculum. Our findings have implications for the potential contribution of Ab responses to defense against microbial diseases because Ab-mediated immunity may be protective, nonprotective, or even deleterious to the host.     

Ig knock-in mice producing anti-carbohydrate antibodies: breakthrough of B cells producing low affinity anti-self antibodies

Natural Abs specific for the carbohydrate Ag Galalpha1-3Galbeta1-4GlcNAc-R (alphaGal) play an important role in providing protective host immunity to various pathogens; yet little is known about how production of these or other anti-carbohydrate natural Abs is regulated. In this study, we describe the generation of Ig knock-in mice carrying functionally rearranged H chain and L chain variable region genes isolated from a B cell hybridoma producing alphaGal-specific IgM Ab that make it possible to examine the development of B cells producing anti-carbohydrate natural Abs in the presence or absence of alphaGal as a self-Ag. Knock-in mice on a alphaGal-deficient background spontaneously developed alphaGal-specific IgM Abs of a sufficiently high titer to mediate rejection of alphaGal expressing cardiac transplants. In the spleen of these mice, B cells expressing alphaGal-specific IgM are located in the marginal zone. In knock-in mice that express alphaGal, B cells expressing the knocked in BCR undergo negative selection via receptor editing. Interestingly, production of low affinity alphaGal-specific Ab was observed in mice that express alphaGal that carry two copies of the knocked in H chain. We suggest that in these mice, receptor editing functioned to lower the affinity for self-Ag below a threshold that would result in overt pathology, while allowing development of low affinity anti-self Abs.     

Biological correlates of capsular (quellung) reactions of Cryptococcus neoformans

The capsular swelling or quellung reaction was reported almost 100 years ago and described the effect of Abs on the appearance of microbial capsules. Despite widespread use to assess Ab binding to capsules, relatively little is known as to the mechanism of this effect or its biological consequences. The fungus Cryptococcus neoformans is an attractive system to study capsule reactions because it has a large polysaccharide capsule that is readily visible by light microscopy. When viewed by differential interference contrast microscopy, binding of mAb to C. neoformans cells produced two distinct capsular reactions that depended on the Ab epitope specificity and the yeast serotype. In the first pattern, termed "rim," the capsule appears transparent with a highly refractive outer edge. In the second pattern, termed "puffy," the capsule appears opaque and lacks a highly refractive outer rim. mAbs that bind with a rim pattern suppress the overall rate of C3 deposition on the yeast via the classical and alternative complement pathways. In contrast, mAbs that bind with a puffy pattern do not affect C3 deposition. Protective and nonprotective IgM mAbs produce rim and puffy patterns, respectively. These results indicate that: 1) capsule reactions are a consequence of Ab-induced changes in capsular refractive index; 2) the type of capsule reaction depends on the Ab specificity; and 3) Ab-induced changes in refractive index correlate with biological activities important for host defense against C. neoformans. Our results provide the first evidence associating distinct capsule reaction patterns with Ab biological activity.     

Outer membrane protein-specific monoclonal antibodies protect SCID mice from fatal infection by the obligate intracellular bacterial pathogen Ehrlichia chaffeensis

Previous studies of Ehrlichia chaffeensis infection in the mouse have demonstrated that passive transfer of polyclonal Abs from resistant immunocompetent mice to susceptible SCID mice ameliorated infection and disease, even when Abs were administered during established infection. To identify particular Abs that could mediate bacterial clearance in vivo, E. chaffeensis-specific mAbs were generated and administered to infected SCID mice. Bacterial infection in the livers was significantly lowered after administration of either of two Abs of different isotypes (IgG2a and IgG3). Moreover, repeated administration of one Ab (Ec56.5; IgG2a) rescued mice from an otherwise lethal infection for at least 5 wk. Both protective Abs recognized the E. chaffeensis major outer membrane protein (OMP)-1g. Further studies revealed that both Abs recognized closely related epitopes within the amino terminus of the first hypervariable region of OMP-1g. Analyses of human sera showed that E. chaffeensis-infected patients also generated serological responses to OMP-1g hypervariable region 1, indicating that humans and mice recognize identical or closely related epitopes. These studies demonstrate that OMP-specific mAbs can mediate bacterial elimination in SCID mice, and indicate that Abs, in the absence of cell-mediated immunity, can play a significant role in host defense during infection by this obligate intracellular bacterium.     

Immunoglobulin M efficacy against Cryptococcus neoformans: mechanism, dose dependence, and prozone-like effects in passive protection experiments

The IgM mAbs 12A1 and 13F1 are protective and nonprotective, respectively, against lethal Cryptococcus neoformans infection in mice. To better understand the variables that contribute to IgM efficacy against C. neoformans, we studied the effects of inoculum size, route of infection, and Ab dose for each of these mAbs. mAb 13F1 did not prolong survival under any condition studied. mAb 12A1 prolonged survival after the administration of certain Ab doses after i.p. infection with defined inocula and promoted phagocytosis, agglutination, and the formation of inflammatory cell rings around yeast cells in vivo. Large Ab doses of mAb 12A1 resulted in either no protection or enhanced infection, consistent with a prozone-like effect. Investigation of this phenomenon revealed that the fungal cell was protected against microbicidal nitrogen-derived oxidants when large amounts of Ab were bound to the C. neoformans capsule. mAb 12A1 was opsonic in vitro for peritoneal, but not splenic or alveolar macrophages. In summary, our results indicate that IgM efficacy against C. neoformans is a function of the route of infection, inoculum, and Ab dose and is associated with its ability to promote opsonization, agglutination, and phagocytic ring formation in vivo. The occurrence of the prozone-like phenomenon implies that high Ab titers are not necessarily beneficial in assuring protection against certain pathogens and that caution should be exercised in using high Ab titer as a measure for vaccine efficacy.     

TCR vaccines against a murine T cell lymphoma: a primary role for antibodies of the IgG2c class in tumor protection

Tumor-associated proteins can act as effective immunotherapeutic targets. Immunization with tumor TCR protein conjugated to the immunogenic protein keyhole limpet hemocyanin (KLH) protects mice from tumor challenge with the murine T cell lymphoma C6VL. The immune mechanisms responsible for this tumor protection are of interest for designing more effective vaccine strategies. Previous studies using depletion experiments had suggested a CD8-mediated component of protection induced by TCR-KLH vaccines. In this study we used CD8alpha knockout, micro MT, and FcgammaR knockout mice to investigate the relative roles of CD8+ T cells and Ab in protective immunity induced by TCR-KLH immunization. We found that CD8+ T cells are not required for tumor protection, although they may contribute to protection. Vaccine-induced Abs are sufficient to mediate protection against this murine T cell lymphoma through an FcR-dependent mechanism. This was confirmed with Ab transfers, which protect challenged mice. Additionally, recombinase-activating gene 1(-/-) splenocytes can mediate Ab-dependent cellular cytotoxicity against this tumor in the presence of bound anti-TCR Abs. IFN-gamma knockout mice demonstrated a requirement for IFN-gamma, probably via generation of IgG2c Abs, in vaccine-induced tumor protection. IFN-gamma knockout mice were not protected by immunization and had a severe impairment in IgG2c Ab production in response to immunization. Although mock-depleted anti-TCR Abs could transfer tumor protection, IgG2c-deficient anti-TCR Abs were unable to transfer tumor protection to wild-type mice. These results suggest that TCR-KLH vaccine-induced tumor protection in the C6VL system is primarily attributable to the induction of IgG2c Abs and humoral immunity.     

Complement is essential for protection by an IgM and an IgG3 monoclonal antibody against experimental, hematogenously disseminated candidiasis

The incidence of life-threatening, hematogenously disseminated candidiasis, which is predominantly caused by Candida albicans, parallels the use of modern medical procedures that adversely affect the immune system. Limited antifungal drug choices and emergence of drug-resistant C. albicans strains indicate the need for novel prevention and therapeutic strategies. We are developing vaccines and Abs that enhance resistance against experimental candidiasis. However, the prevalence of serum anti-Candida Abs in candidiasis patients has led to the misconception that Abs are not protective. To explain the apparent discrepancy between such clinical observations and our work, we compared functional activities of C. albicans-specific protective and nonprotective mAbs. Both kinds of Abs are agglutinins that fix complement and are specific for cell surface mannan, but the protective Abs recognize beta-mannan, and the nonprotective Ab is specific for alpha-mannan. By several indirect and direct measures, the protective mAbs more efficiently bind complement factor C3 to the yeast cell than do nonprotective Ab. We hypothesize that the C3 deposition causes preferential association of blood-borne fungi with host phagocytic cells that are capable of killing the fungus. We conclude from these results that the protective potential of Abs is dependent on epitope specificity, serum titer, and ability to rapidly and efficiently fix complement to the fungal surface. The mechanism of protection appears to be associated with enhanced phagocytosis and killing of the fungus.