Complement and Fc function are required for optimal antibody prophylaxis against Pneumocystis carinii pneumonia

Synthetic conjugate peptide Fba-Met6 (MP12) induces complement-mediated resistance against disseminated Candida albicans

The fungal genus Candida includes common commensals of the human mucosal membranes, and the most prevalently isolated species, C. albicans, poses a threat of candidemia and disseminated infection associated with an unacceptably high mortality rate and an immense $4 billion burden (US) yearly. Nevertheless, the demand for a vaccine remains wholly unfulfilled and increasingly pressing. We developed a double-peptide construct that is feasible for use in humans with the intention of preventing morbid infection by targeting epitopes derived from fructose bisphosphate aldolase (Fba) and methionine synthase (Met6) which are expressed on the C. albicans cell surface. To test the applicability of the design, we vaccinated mice via the intramuscular (IM) route with the conjugate denoted Fba-Met6 MP12 and showed that the vaccine enhanced survival against a lethal challenge. Because overall endpoint IgG1 and IgG2a antibody titers were robust and these mouse subclasses are associated with protective functionality, we investigated the potential of Fba and Met6 specific antibodies to facilitate the well-defined anti-Candida response by complement, which opsonizes fungi for degradation by primary effectors. Notably, reductions in the fungal burdens and enhanced survival were both abrogated in MP12-vaccinated mice that were pre-challenge dosed with cobra venom factor (CVF), a complement depleting factor. Altogether, we demonstrated that complement is relevant to MP12-based protection against disseminated C. albicans, delineating that a novel, multivalent targeted vaccine against proteins on the surface of C. albicans can enhance the natural response to infection.

Combination Immunotherapy with Passive Antibody and Sulfasalazine Accelerates Fungal Clearance and Promotes the Resolution of Pneumocystis-Associated Immunopathogenesis

The pulmonary immune response protects healthy individuals against Pneumocystis pneumonia (PcP). However, the immune response also drives immunopathogenesis in patients who develop severe PcP, and it is generally accepted that optimal treatment requires combination strategies that promote fungal killing and also provide effective immunomodulation. The anti-inflammatory drug sulfasalazine programs macrophages for enhanced Pneumocystis phagocytosis and also suppresses PcP-related immunopathogenesis. Anti-Pneumocystis antibody opsonizes Pneumocystis organisms for greater phagocytosis and may also mask antigens that drive immunopathogenesis. Thus, we hypothesized that combining antibody and sulfasalazine would have the dual benefit of enhancing fungal clearance while dampening immunopathogenesis and allow the rescue of severe PcP. To model a clinically relevant treatment scenario in mice, therapeutic interventions were withheld until clear symptoms of pneumonia were evident. When administered individually, both passive antibody and sulfasalazine improved pulmonary function and enhanced Pneumocystis clearance to similar degrees. However, combination treatment with antibody and sulfasalazine produced a more rapid improvement, with recovery of body weight, a dramatic improvement in pulmonary function, reduced lung inflammation, and the rapid clearance of the Pneumocystis organisms. Accelerated fungal clearance in the combination treatment group was associated with a significant increase in macrophage phagocytosis of Pneumocystis Both passive antibody and sulfasalazine resulted in the suppression of Th1 cytokines and a marked increase in lung macrophages displaying an alternatively activated phenotype, which were enhanced by combination treatment. Our data support the concept that passive antibody and sulfasalazine could be an effective and specific adjunctive therapy for PcP, with the potential to accelerate fungal clearance while attenuating PcP-associated immunopathogenesis.

Transcriptomic and Proteomic Approaches to Finding Novel Diagnostic and Immunogenic Candidates in Pneumocystis

Pneumocystis pneumonia is the most common serious opportunistic infection in patients with HIV/AIDS. Furthermore, Pneumocystis pneumonia is a feared complication of the immunosuppressive drug regimens used to treat autoimmunity, malignancy, and posttransplantation rejection. With an increasing at-risk population, there is a strong need for novel approaches to discover diagnostic and vaccine targets. There are multiple challenges to finding these targets, however. First, Pneumocystis has a largely unannotated genome. To address this, we evaluated each protein encoded within the Pneumocystis genome by comparisons to proteins encoded within the genomes of other fungi using NCBI BLAST. Second, Pneumocystis relies on a multiphasic life cycle, as both the transmissible form (the ascus) and the replicative form (the trophozoite [troph]) reside within the alveolar space of the host. To that end, we purified asci and trophs from Pneumocystis murina and utilized transcriptomics to identify differentially regulated genes. Two such genes, Arp9 and Sp, are differentially regulated in the ascus and the troph, respectively, and can be utilized to characterize the state of the Pneumocystis life cycle in vivo Gsc1, encoding a β-1,3-glucan synthase with a large extracellular domain previously identified using surface proteomics, was more highly expressed on the ascus form of Pneumocystis GSC-1 ectodomain immunization generated a strong antibody response that demonstrated the ability to recognize the surface of the Pneumocystis asci. GSC-1 ectodomain immunization was also capable of reducing ascus burden following primary challenge with Pneumocystis murina Finally, mice immunized with the GSC-1 ectodomain had limited fungal burden following natural transmission of Pneumocystis using a cohousing model.IMPORTANCE The current report enhances our understanding of Pneumocystis biology in a number of ways. First, the current study provided a preliminary annotation of the Pneumocystis murina genome, addressing a long-standing issue in the field. Second, this study validated two novel transcripts enriched in the two predominant life forms of Pneumocystis These findings allow better characterization of the Pneumocystis life cycle in vivo and could be valuable diagnostic tools. Furthermore, this study outlined a novel pipeline of -omics techniques capable of revealing novel antigens (e.g., GSC-1) for the development of vaccines against Pneumocystis.

Effects of clinical and environmental factors on bronchoalveolar antibody responses to Pneumocystis jirovecii: A prospective cohort study of HIV+ patients

BACKGROUND

Humoral immunity plays an important role against Pneumocystis jirovecii infection, yet clinical and environmental factors that impact bronchoalveolar antibody responses to P. jirovecii remain uncertain.

METHODS

From October 2008-December 2011 we enrolled consecutive HIV-infected adults admitted to San Francisco General Hospital (SFGH) who underwent bronchoscopy for suspected Pneumocystis pneumonia (PCP). We used local air quality monitoring data to assign ozone, nitrogen dioxide, and fine particulate matter exposures within 14 days prior to hospital admission. We quantified serum and bronchoalveolar lavage fluid (BALF) antibody responses to P. jirovecii major surface glycoprotein (Msg) recombinant constructs using ELISA. We then fit linear regression models to determine whether PCP and ambient air pollutants were associated with bronchoalveolar antibody responses to Msg.

RESULTS

Of 81 HIV-infected patients enrolled, 47 (58%) were diagnosed with current PCP and 9 (11%) had a prior history of PCP. The median CD4+ count was 51 cells/μl (IQR 15-129) and 44% were current smokers. Serum antibody responses to Msg were statistically significantly predictive of BALF antibody responses, with the exception of IgG responses to MsgC8 and MsgC9. Prior PCP was associated with increased BALF IgA responses to Msg and current PCP was associated with decreased IgA responses. For instance, among patients without current PCP, those with prior PCP had a median 73.2 U (IQR 19.2-169) IgA response to MsgC1 compared to a 5.00 U (3.52-12.6) response among those without prior PCP. Additionally, current PCP predicted a 22.5 U (95%CI -39.2, -5.82) lower IgA response to MsgC1. Ambient ozone within the two weeks prior to hospital admission was associated with decreased BALF IgA responses to Msg while nitrogen dioxide was associated with increased IgA responses.

CONCLUSIONS

PCP and ambient air pollutants were associated with BALF IgA responses to P. jirovecii in HIV-infected patients evaluated for suspected PCP.

Transcriptomic Analysis Reveals Significant B Lymphocyte Suppression in Corticosteroid-Treated Hosts with Pneumocystis Pneumonia

Pneumocystis pneumonia (PCP) is an opportunistic, infectious disease that is prevalent in immunosuppressed hosts. Corticosteroid treatment is the most significant risk factor for patients with PCP who are human immunodeficiency virus negative, although little is known about how corticosteroids alter the host defense against Pneumocystis infection. In the present study, we used transcriptome analysis to examine the immune response in the lungs of corticosteroid-treated PCP mice. The results showed down-regulation in the genes related to both native immunity, such as antigen processing and presentation, inflammatory response, and phagocytosis, as well as B and T lymphocyte immunity. The repression of gene expression, corresponding to B cell immunity, including B cell signaling, homeostasis, and Ig production, was prominent. The finding was confirmed by quantitative PCR of mouse lungs and the peripheral blood of patients with PCP. Flow cytometry also revealed a significant depletion of B cells in corticosteroid-treated PCP mice. Our study has highlighted that corticosteroid treatment suppresses the B cell immunity in the PCP host, which is likely one of the main reasons that corticosteroid treatment may stimulate PCP development.

Immunization with Pneumocystis Cross-Reactive Antigen 1 (Pca1) Protects Mice against Pneumocystis Pneumonia and Generates Antibody to Pneumocystis jirovecii

Pneumocystis pneumonia (PcP) is a life-threatening infection that affects immunocompromised individuals. Nearly half of all PcP cases occur in those prescribed effective chemoprophylaxis, suggesting that additional preventive methods are needed. To this end, we have identified a unique mouse Pneumocystis surface protein, designated Pneumocystis cross-reactive antigen 1 (Pca1), as a potential vaccine candidate. Mice were immunized with a recombinant fusion protein containing Pca1. Subsequently, CD4⁺ T cells were depleted, and the mice were exposed to Pneumocystis murina Pca1 immunization completely protected nearly all mice, similar to immunization with whole Pneumocystis organisms. In contrast, all immunized negative-control mice developed PcP. Unexpectedly, Pca1 immunization generated cross-reactive antibody that recognized Pneumocystis jirovecii and Pneumocystis carinii Potential orthologs of Pca1 have been identified in P. jirovecii Such cross-reactivity is rare, and our findings suggest that Pca1 is a conserved antigen and potential vaccine target. The evaluation of Pca1-elicited antibodies in the prevention of PcP in humans deserves further investigation.

Oral Immunization of Mice with Live Pneumocystis murina Protects against Pneumocystis Pneumonia

Pneumocystis pneumonia is a major cause of morbidity and mortality in immunocompromised patients, particularly those infected with HIV. In this study, we evaluated the potential of oral immunization with live Pneumocystis to elicit protection against respiratory infection with Pneumocystis murina. C57BL/6 mice vaccinated with live P. murina using a prime-boost vaccination strategy were protected from a subsequent lung challenge with P. murina at 2, 7, 14, and 28 d postinfection even after CD4(+) T cell depletion. Specifically, vaccinated immunocompetent mice had significantly faster clearance than unvaccinated immunocompetent mice and unvaccinated CD4-depleted mice remained persistently infected with P. murina. Vaccination also increased numbers of CD4(+) T cells, CD8(+) T cells, CD19(+) B cells, and CD11b(+) macrophages in the lungs following respiratory infection. In addition, levels of lung, serum, and fecal P. murina-specific IgG and IgA were increased in vaccinated animals. Furthermore, administration of serum from vaccinated mice significantly reduced Pneumocystis lung burden in infected animals compared with control serum. We also found that the diversity of the intestinal microbial community was altered by oral immunization with P. murina. To our knowledge, our data demonstrate for the first time that an oral vaccination strategy prevents Pneumocystis infection.

X-linked Agammaglobulinemia With Normal Immunoglobulin and Near-Normal Vaccine Seroconversion

We present a 22-month-old boy with X-linked agammaglobulinemia masked by normal immunoglobulin levels and vaccine seroconversion. Diagnosis was made after strong clinical suspicion of immune deficiency led to identification of markedly reduced B-cell numbers and confirmation with identification of a novel Bruton tyrosine kinase gene mutation. He was commenced on replacement immunoglobulin therapy with excellent clinical improvement. This case highlights the variability of phenotypic presentation and apparent disunity between routine immunologic investigations and severe disease in X-linked agammaglobulinemia, necessitating clinical acumen to make the diagnosis.

Complement system in lung disease

In addition to its established contribution to innate immunity, recent studies have suggested novel roles for the complement system in the development of various lung diseases. Several studies have demonstrated that complement may serve as a key link between innate and adaptive immunity in a variety of pulmonary conditions. However, the specific contributions of complement to lung diseases based on innate and adaptive immunity are just beginning to emerge. Elucidating the role of complement-mediated immune regulation in these diseases will help to identify new targets for therapeutic interventions.

Pathological and protective immunity to Pneumocystis infection

Pneumocystis jirovecii is a common opportunistic infection in the HIV-positive population and is re-emerging as a growing clinical concern in the HIV-negative immunosuppressed population. Newer targeted immunosuppressive therapies and the discovery of rare genetic mutations have furthered our understanding of the immunity required to clear Pneumocystis infection. The immune system can also mount a pathologic response against Pneumocystis following removal of immunosuppression and result in severe damage to the host lung. The current review will examine the most recent epidemiologic studies about the incidence of Pneumocystis in the HIV-positive and HIV-negative populations in the developing and developed world and will detail methods of diagnosis for Pneumocystis pneumonia. Finally, this review aims to summarize the known mediators of immunity to Pneumocystis and detail the pathologic immune response leading to Pneumocystis-related immune reconstitution inflammatory syndrome.

The protective role of immunoglobulins in fungal infections and inflammation

Increased incidence of fungal infections in the immunocompromised individuals and fungi-mediated allergy and inflammatory conditions in immunocompetent individuals is a cause of concern. Consequently, there is a need for efficient therapeutic alternatives to treat fungal infections and inflammation. Several studies have demonstrated that antibodies or immunoglobulins have a role in restricting the fungal burden and their clearance. However, based on the data from monoclonal antibodies, it is now evident that the efficacy of antibodies in fungal infections is dependent on epitope specificity, abundance of protective antibodies, and their isotype. Antibodies confer protection against fungal infections by multiple mechanisms that include direct neutralization of fungi and their antigens, inhibition of growth of fungi, modification of gene expression, signaling and lipid metabolism, causing iron starvation, inhibition of polysaccharide release, and biofilm formation. Antibodies promote opsonization of fungi and their phagocytosis, complement activation, and antibody-dependent cell toxicity. Passive administration of specific protective monoclonal antibodies could also prove to be beneficial in drug resistance cases, to reduce the dosage and associated toxic symptoms of anti-fungal drugs. The longer half-life of the antibodies and flexibilities to modify their structure/forms are additional advantages. The clinical data obtained with two monoclonal antibodies should incite interests in translating pre-clinical success into the clinics. The anti-inflammatory and immunoregulatory role of antibodies in fungal inflammation could be exploited by intravenous immunoglobulin or IVIg.

Dual role for Fcγ receptors in host defense and disease in Borrelia burgdorferi-infected mice

Arthritis in mice infected with the Lyme disease spirochete, Borrelia burgdorferi, results from the influx of innate immune cells responding to the pathogen in the joint and is influenced in part by mouse genetics. Production of inflammatory cytokines by innate immune cells in vitro is largely mediated by Toll-like receptor (TLR) interaction with Borrelia lipoproteins, yet surprisingly mice deficient in TLR2 or the TLR signaling molecule MyD88 still develop arthritis comparable to that seen in wild type mice after B. burgdorferi infection. These findings suggest that other, MyD88-independent inflammatory pathways can contribute to arthritis expression. Clearance of B. burgdorferi is dependent on the production of specific antibody and phagocytosis of the organism. As Fc receptors (FcγR) are important for IgG-mediated clearance of immune complexes and opsonized particles by phagocytes, we examined the role that FcγR play in host defense and disease in B. burgdorferi-infected mice. B. burgdorferi-infected mice deficient in the Fc receptor common gamma chain (FcεR_γ^−/− mice) harbored ~10 fold more spirochetes than similarly infected wild type mice, and this was associated with a transient increase in arthritis severity. While the elevated pathogen burdens seen in B. burgdorferi-infected MyD88^−/− mice were not affected by concomitant deficiency in FcγR, arthritis was reduced in FcεR_γ^−/−MyD88^−/− mice in comparison to wild type or single knockout mice. Gene expression analysis from infected joints demonstrated that absence of both MyD88 and FcγR lowers mRNA levels of proteins involved in inflammation, including Cxcl1 (KC), Xcr1 (Gpr5), IL-1beta, and C reactive protein. Taken together, our results demonstrate a role for FcγR-mediated immunity in limiting pathogen burden and arthritis in mice during the acute phase of B. burgdorferi infection, and further suggest that this pathway contributes to the arthritis that develops in B. burgdorferi-infected MyD88^−/− mice.

Novel pneumocystis antigen discovery using fungal surface proteomics

Pneumonia due to the fungus Pneumocystis jirovecii is a life-threatening infection that occurs in immunocompromised patients. The inability to culture the organism as well as the lack of an annotated genome has hindered antigen discovery that could be useful in developing novel vaccine- or antibody-based therapies as well as diagnostics for this infection. Here we report a novel method of surface proteomics analysis of Pneumocystis murina that reliably detected putative surface proteins that are conserved in Pneumocystis jirovecii. This technique identified novel CD4(+) T-cell epitopes as well as a novel B-cell epitope, Meu10, which encodes a glycosylphosphatidylinositol (GPI)-anchored protein thought to be involved in ascospore assembly. The described technique should facilitate the discovery of novel target proteins for diagnostics and therapeutics for Pneumocystis infection.

Ambient air pollution associated with suppressed serologic responses to Pneumocystis jirovecii in a prospective cohort of HIV-infected patients with Pneumocystis pneumonia

BACKGROUND

Ambient air pollution (AAP) may be associated with increased risk for Pneumocystis pneumonia (PCP). The mechanisms underlying this association remain uncertain.

OBJECTIVES

To determine if real-life exposures to AAP are associated with suppressed IgM antibody responses to P. jirovecii in HIV-infected (HIV+) patients with active PCP, and to determine if AAP, mediated by suppressed serologic responses to Pneumocystis, is associated with adverse clinical outcomes.

METHODS

We conducted a prospective cohort study in HIV+ patients residing in San Francisco and admitted to San Francisco General Hospital with microscopically confirmed PCP. Our AAP predictors were ambient air concentrations of particulate matter of < 10 µm in diameter (PM10) and < 2.5 µm in diameter (PM2.5), nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2) measured immediately prior to hospital admission and 2 weeks prior to admission. Our primary outcomes were the IgM serologic responses to four recombinant P. jirovecii major surface glycoprotein (Msg) constructs: MsgC1, MsgC3, MsgC8, and MsgC9.

RESULTS

Elevated PM10 and NO2 exposures immediately prior to and two weeks prior to hospital admission were associated with decreased IgM antibody responses to P. jirovecii Msg. For exposures immediately prior to admission, every 10 µg/m(3) increase in PM10 was associated with a 25 to 35% decrease in IgM responses to Msg (statistically significant for all the Msg constructs), and every 10 ppb increase in NO2 was associated with a 19-45% decrease in IgM responses to Msg (statistically significant for MsgC8 and MsgC9). Similar findings were seen with exposures two weeks prior to admission, but for fewer of the Msg constructs.

CONCLUSIONS

Real life exposures to PM10 and NO2 were associated with suppressed IgM responses to P. jirovecii Msg in HIV+ patients admitted with PCP, suggesting a mechanism of immunotoxicity by which AAP increases host susceptibility to pulmonary infection.

Innate and adaptive antifungal immune responses: partners on an equal footing

Adaptive immunity has long been regarded as the major player in protection against most fungal infections. Mounting evidence suggest however, that both innate and adaptive responses intricately collaborate to produce effective antifungal protection. Dendritic cells (DCs) play an important role in initiating and orchestrating antifungal immunity; neutrophils, macrophages and other phagocytes also participate in recognising and eliminating fungal pathogens. Adaptive immunity provides a wide range of effector and regulatory responses against fungal infections. Th1 responses protect against most forms of mycoses but they associate with significant inflammation and limited pathogen persistence. By contrast, Th2 responses enhance persistence of and tolerance to fungal infections thus permitting the generation of long-lasting immunological memory. Although the role of Th17 cytokines in fungal immunity is not fully understood, they can enhance proinflammatory or anti-inflammatory responses or play a regulatory role in fungal immunity all depending on the pathogen, site/phase of infection and host immunostatus. T regulatory cells balance the activities of various Th cell subsets thereby permitting inflammation and protection on the one hand and allowing for tolerance and memory on the other. Here, recent developments in fungal immunity research are reviewed as means of tracing the emergence of a refined paradigm where innate and adaptive responses are viewed in the same light.

Engineered Fc variant antibodies with enhanced ability to recruit complement and mediate effector functions

Engineering the antibody Fc region to enhance the cytotoxic activity of therapeutic antibodies is currently an active area of investigation. The contribution of complement to the mechanism of action of some antibodies that target cancers and pathogens makes a compelling case for its optimization. Here we describe the generation of a series of Fc variants with enhanced ability to recruit complement. Variants enhanced the cytotoxic potency of an anti-CD20 antibody up to 23-fold against tumor cells in CDC assays, and demonstrated a correlated increase in C1q binding affinity. Complement-enhancing substitutions combined additively, and in one case synergistically, with substitutions previously engineered for improved binding to Fc gamma receptors. The engineered combinations provided a range of effector function activities, including simultaneously enhanced CDC, ADCC, and phagocytosis. Variants were also effective at boosting the effector function of antibodies targeting the antigens CD40 and CD19, in the former case enhancing CDC over 600-fold, and in the latter case imparting complement-mediated activity onto an IgG1 antibody that was otherwise incapable of it. This work expands the toolkit of modifications for generating monoclonal antibodies with improved therapeutic potential and enables the exploration of optimized synergy between Fc gamma receptors and complement pathways for the destruction of tumors and infectious pathogens.

A recombinant flagellin-poxvirus fusion protein vaccine elicits complement-dependent protection against respiratory challenge with vaccinia virus in mice

Bacterial flagellin is a potent adjuvant that enhances adaptive immune responses to a variety of protein antigens. The vaccinia virus antigens L1R and B5R are highly immunogenic in the context of the parent virus, but recombinant forms of the proteins are only weakly immunogenic. Therefore we evaluated the humoral response to these antigens in mice when flagellin was used as an adjuvant. Flagellin-L1R and flagellin-B5R fusion proteins were more potent than flagellin, L1R, and B5R as separate proteins. At least three immunizations with flagellin-L1R and flagellin-B5R fusion proteins were required to confer protection in mice against challenge with vaccinia virus. Immune mice exhibited only limited signs of disease following challenge. Additionally, virus neutralization titers correlated with protection. Depletion of complement using cobra venom factor resulted in a marked decrease in the survival of immunized mice after challenge with vaccinia virus. Our results are consistent with the conclusion that flagellin-L1R and flagellin-B5R fusion proteins are effective in eliciting protective immunity against vaccinia virus that is dependent, in large part, on complement.

Current understanding of Pneumocystis immunology

Pneumocystis jirovecii is the opportunistic fungal organism that causes Pneumocystis pneumonia (PCP) in humans. Similar to other opportunistic pathogens, Pneumocystis causes disease in individuals who are immunocompromised, particularly those infected with HIV. PCP remains the most common opportunistic infection in patients with AIDS. Incidence has decreased greatly with the advent of HAART. However, an increase in the non-HIV immunocompromised population, noncompliance with current treatments, emergence of drug-resistant strains and rise in HIV(+) cases in developing countries makes Pneumocystis a pathogen of continued interest and a public health threat. A great deal of research interest has addressed therapeutic interventions to boost waning immunity in the host to prevent or treat PCP. This article focuses on research conducted during the previous 5 years regarding the host immune response to Pneumocystis, including innate, cell-mediated and humoral immunity, and associated immunotherapies tested against PCP.

Complement and fungal pathogens: an update

Fungal infections are a serious complication in immunocompromised patients such as human immunodeficiency virus-infected individuals, patients with organ transplantations or with haematological neoplasia. The lethality of opportunistic fungal infection is high despite a growing arsenal of antimycotic drugs, implying the urgent need for supportive immunological therapies to strengthen the current inefficient antimicrobial defences of the immunocompromised host. Therefore, increasing effort has been directed to investigating the interplay between fungi and the host immunity and thus to find starting points for additional therapeutic approaches. In this article, we review the actual state of the art concerning the role of complement in the pathogenesis of fungal infections. Important aspects include the activation of the complement system by the fungal pathogen, the efficiency of the complement-associated antimicrobial functions and the arsenal of immune evasion strategies applied by the fungi. The twin functions of complement as an interactive player of the innate immunity and at the same time as a modulator of the adaptive immunity make this defence weapon a particularly interesting therapeutic candidate to mobilise a more effective immune response and to strengthen in one fell swoop a broad spectrum of different immune reactions. However, we also mention the 'Yin-Yang' nature of the complement system in fungal infections, as growing evidence assigns to complement a contributory part in the pathogenesis of fungus-induced allergic manifestations.

X-linked agammaglobulinemia: report on a United States registry of 201 patients

X-linked agammaglobulinemia (XLA) is a primary immunodeficiency caused by mutations in the gene for Bruton tyrosine kinase (BTK) that result in the deficient development of B lymphocytes and hypogammaglobulinemia. Because the disorder is uncommon, no single institution has had sufficient numbers of patients to develop a comprehensive clinical picture of the disorder. Accordingly, a national registry of United States residents with XLA was established in 1999 to provide an updated clinical view of the disorder in a large cohort of patients. A total of 201 patients were registered by 66 physicians. The estimated birth rate for the 10-year period of 1988-1997 was 1/379,000. Infection was the most common initial clinical presentation (85%), followed by a positive family history (41%) and neutropenia (11%). Although the average age of diagnosis was younger in patients with a positive family history (mean, 2.59 yr) than in patients with a negative family history (mean, 5.37 yr) (p < 0.001), only 34.5% of patients with a positive family history at the time of their birth were diagnosed before clinical symptoms developed-that is, based on family history alone. Seventy percent of patients had at least 1 episode of otitis, 62% at least 1 episode of pneumonia, 60% at least 1 episode of sinusitis, 23% at least 1 episode of chronic/recurrent diarrhea, 21% at least 1 episode of conjunctivitis, 18% at least 1 episode of pyoderma and/or cellulitis, 11% at least 1 episode of meningitis/encephalitis, 10% at least 1 episode of sepsis, 8% at least 1 episode of septic arthritis, 6% at least 1 episode of hepatitis, and 3% at least 1 episode of osteomyelitis. Fourteen of 201 (6.9%) patients were dead at the time they were entered in the Registry. However, in a prospective 4 /4-year follow-up of living patients, only 3/80 (3.75%) patients died. Causes of death included disseminated enterovirus infection (n = 6), pulmonary insufficiency (n = 5), adenovirus infection (n = 1), sepsis (n = 1), acquired immunodeficiency disease syndrome (AIDS) (n = 1), myocarditis (n = 1), hepatitis (n = 2), and stem cell transplantation (n = 1).