Relationship of pneumocystis antibody response to severity of chronic obstructive pulmonary disease

A therapeutic vaccine strategy to prevent Pneumocystis pneumonia in an immunocompromised host in a non-human primate model of HIV and Pneumocystis co-infection

Introduction

Pneumocystis is a ubiquitous fungal pathogen that causes pneumonia (PCP) and pulmonary sequelae in HIV-infected individuals and other immunocompromised populations. With the success of anti-retroviral therapy for HIV-infected individuals the frequency of PCP in that population has decreased, however, PCP remains a significant cause of morbidity and mortality in individuals with hematologic and solid malignancies, and in individuals treated with immunosuppressive therapies for autoimmune diseases, and following bone marrow and solid organ transplantation. Despite the clinical need, there is no approved vaccine to prevent PCP in vulnerable populations. The ultimate goal of the field is to develop an effective vaccine that can overcome immune deficits in at risk populations and induce long-lasting protective immunity to Pneumocystis. Toward this goal, our laboratory has established a model of PCP co-infection in simian immunodeficiency virus (SIV)-infected non-human primates (NHP) and identified a recombinant protein sub-unit vaccine, KEX1, that induces robust anti-Pneumocystis immunity in immune-competent macaques that is durable and prevents PCP following simian immunodeficiency virus (SIV)-induced immunosuppression. Type I, or invariant natural killer T (iNKT) cells have the potential to provide B cell help under conditions of reduced CD4+ T cell help.

Methods

In the present study, we used the SIV model of HIV infection to address whether therapeutic vaccination with the iNKT cell-activating adjuvant α-galactosylceramide (α-GC) and KEX1 (α-GC+KEX1) can effectively boost anti-Pneumocystis humoral immunity following virus-induced immunosuppression.

Results

Immunization of antigen-experienced NHPs with α-GC+KEX1 during the early chronic phase of SIV-infection significantly boosted anti-Pneumocystis humoral immunity by increasing memory B cells and antibody titers, and enhanced titer durability during SIV-induced immunosuppression. This therapeutic vaccination strategy boosted anti-Pneumocystis immune responses during SIV-infection and contributed to protection against Pneumocystis co-infection in KEX1-vaccinated macaques.

Conclusion

These studies present a novel strategy for stimulating durable anti-Pneumocystis humoral immunity in the context of complex, chronic SIV-induced immunosuppression and may be further applied to immunization of other immunosuppressed populations, and toward other common recall antigens.

Immunogenicity and protective efficacy of a pan-fungal vaccine in preclinical models of aspergillosis, candidiasis, and pneumocystosis

Invasive fungal infections cause over 1.5 million deaths worldwide. Despite increases in fungal infections as well as the numbers of individuals at risk, there are no clinically approved fungal vaccines. We produced a "pan-fungal" peptide, NXT-2, based on a previously identified vaccine candidate and homologous sequences from Pneumocystis, Aspergillus,Candida, and Cryptococcus. We evaluated the immunogenicity and protective capacity of NXT-2 in murine and nonhuman primate models of invasive aspergillosis, systemic candidiasis, and pneumocystosis. NXT-2 was highly immunogenic and immunized animals had decreased mortality and morbidity compared to nonvaccinated animals following induction of immunosuppression and challenge with Aspergillus, Candida, or Pneumocystis. Data in multiple animal models support the concept that immunization with a pan-fungal vaccine prior to immunosuppression induces broad, cross-protective antifungal immunity in at-risk individuals.

A comprehensive clinical guide for Pneumocystis jirovecii pneumonia: a missing therapeutic target in HIV-uninfected patients

INTRODUCTION

Pneumocystis jirovecii is an opportunistic, human-specific fungus that causes Pneumocystis pneumonia (PCP). PCP symptoms are nonspecific. A patient with P. jirovecii and another lung infection faces a diagnostic challenge. It may be difficult to determine which of these agents is responsible for the clinical symptoms, preventing effective treatment. Diagnostic and treatment efforts have been made more difficult by the rising frequency with which coronavirus 2019 (COVID-19) and PCP co-occur.

AREAS COVERED

Herein, we provide a comprehensive review of clinical and pharmacological recommendations along with a literature review of PCP in immunocompromised patients focusing on HIV-uninfected patients.

EXPERT OPINION

PCP may be masked by identifying co-existing pathogens that are not necessarily responsible for the observed infection. Patients with severe form COVID-19 should be examined for underlying immunodeficiency, and co-infections must be considered as co-infection with P. jirovecii may worsen COVID-19's severity and fatality. PCP should be investigated in patients with PCP risk factors who come with pneumonia and suggestive radiographic symptoms but have not previously received PCP prophylaxis. PCP prophylaxis should be explored in individuals with various conditions that impair the immune system, depending on their PCP risk.

Demographic and Socioeconomic Factors Associated with Fungal Infection Risk, United States, 2019

Diagnosis disproportionately affected minority and low-income populations, underscoring the need for broad public health interventions.

Fungal infections cause substantial rates of illness and death. Interest in the association between demographic factors and fungal infections is increasing. We analyzed 2019 US hospital discharge data to assess factors associated with fungal infection diagnosis, including race and ethnicity and socioeconomic status. We found male patients were 1.5–3.5 times more likely to have invasive fungal infections diagnosed than were female patients. Compared with hospitalizations of non-Hispanic White patients, Black, Hispanic, and Native American patients had 1.4–5.9 times the rates of cryptococcosis, pneumocystosis, and coccidioidomycosis. Hospitalizations associated with lower-income areas had increased rates of all fungal infections, except aspergillosis. Compared with younger patients, fungal infection diagnosis rates, particularly for candidiasis, were elevated among persons >65 years of age. Our findings suggest that differences in fungal infection diagnostic rates are associated with demographic and socioeconomic factors and highlight an ongoing need for increased physician evaluation of risk for fungal infections.

Prevalence and Healthcare Burden of Fungal Infections in the United States, 2018

Background

Fungal infections are responsible for >1.5 million deaths globally per year, primarily in those with compromised immune function. This is concerning as the number of immunocompromised patients, especially in those without human immunodeficiency virus (HIV), has risen in the past decade. The purpose of this analysis was to provide the current prevalence and impact of fungal disease in the United States.

Methods

We analyzed hospital discharge data from the most recent (2018) Healthcare Cost and Utilization Project National Inpatient Sample, and outpatient visit data from the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey. Costs are presented in 2018 United States (US) dollars.

Results

In the 35.5 million inpatient visits documented in 2018 in the US, approximately 666 235 fungal infections were diagnosed, with an estimated attributable cost of $6.7 billion. Aspergillus, Pneumocystis, and Candida infections accounted for 76.3% of fungal infections diagnosed, and 81.1% of associated costs. Most fungal disease occurred in patients with elevated risk of infection. The visit costs, lengths of stay, and risks of mortality in this population were more than twice that of those without fungal diagnoses. A further 6.6 million fungal infections were diagnosed during outpatient visits.

Conclusions

Fungal disease is a serious clinical concern with substantial healthcare costs and significant increases in morbidity and mortality, particularly among predisposed patients. Increased surveillance, standardized treatment guidelines, and improvement in diagnostics and therapeutics are needed to support the rising numbers of at-risk patients.

Relationship of Pneumocystis antibody responses to paediatric asthma severity

BACKGROUND

Although asthma is the most commonly diagnosed respiratory disease, its pathogenesis is complex, involving both genetic and environmental factors. A role for the respiratory microbiome in modifying asthma severity has been recently recognised. Airway colonisation by Pneumocystis jirovecii has previously been associated with multiple chronic lung diseases, including chronic obstructive pulmonary disease (COPD) and severe asthma (SA). Decreased incidence of Pneumocystis pneumonia in HIV-infected individuals and reduced severity of COPD is associated with naturally occurring antibody responses to the Pneumocystis antigen, Kexin (KEX1).

METHODS

104 paediatric patients were screened for KEX1 IgG reciprocal end point titre (RET), including 51 with SA, 20 with mild/moderate asthma, 20 non-asthma and 13 with cystic fibrosis (CF) in a cross-sectional study.

RESULTS

Patients with SA had significantly reduced Pneumocystis KEX1 titres compared with patients with mild/moderate asthma (p=0.018) and CF (p=0.003). A binary KEX1 RET indicator was determined at a threshold of KEX1 RET=1000. Patients with SA had 4.40 (95% CI 1.28 to 13.25, p=0.014) and 17.92 (95% CI 4.15 to 66.62, p<0.001) times the odds of falling below that threshold compared with mild/moderate asthma and patients with CF, respectively. Moreover, KEX1 IgG RET did not correlate with tetanus toxoid IgG (r=0.21, p=0.82) or total IgE (r=0.03, p=0.76), indicating findings are specific to antibody responses to KEX1.

CONCLUSIONS

Paediatric patients with SA may be at higher risk for chronic Pneumocystis infections and asthma symptom exacerbation due to reduced levels of protective antibodies. Plasma KEX1 IgG titre may be a useful parameter in determining the clinical course of treatment for paediatric patients with asthma.

Pneumocystis Pneumonia: Immunity, Vaccines, and Treatments

For individuals who are immunocompromised, the opportunistic fungal pathogen Pneumocystis jirovecii is capable of causing life-threatening pneumonia as the causative agent of Pneumocystis pneumonia (PCP). PCP remains an acquired immunodeficiency disease (AIDS)-defining illness in the era of antiretroviral therapy. In addition, a rise in non-human immunodeficiency virus (HIV)-associated PCP has been observed due to increased usage of immunosuppressive and immunomodulating therapies. With the persistence of HIV-related PCP cases and associated morbidity and mortality, as well as difficult to diagnose non-HIV-related PCP cases, an improvement over current treatment and prevention standards is warranted. Current therapeutic strategies have primarily focused on the administration of trimethoprim-sulfamethoxazole, which is effective at disease prevention. However, current treatments are inadequate for treatment of PCP and prevention of PCP-related death, as evidenced by consistently high mortality rates for those hospitalized with PCP. There are no vaccines in clinical trials for the prevention of PCP, and significant obstacles exist that have slowed development, including host range specificity, and the inability to culture Pneumocystis spp. in vitro. In this review, we overview the immune response to Pneumocystis spp., and discuss current progress on novel vaccines and therapies currently in the preclinical and clinical pipeline.

Clinical characteristics and prevalence of dihydropteroate synthase gene mutations in Pneumocystis jirovecii-infected AIDS patients from low endemic areas of China

Pneumocystis pneumonia (PCP) is an opportunistic and potentially life-threatening infection of AIDS patients caused by the fungus Pneumocystis jirovecii (P. jirovecii). Trimethoprim-sulfamethoxazole (TMP-SMX) is the most commonly used drug combination in the treatment and prophylaxis of PCP. However, with long-term use of this combination, mutations in the dihydropteroate synthase (DHPS) gene of P. jirovecii bring about the development of resistance. Data on the prevalence of P. jirovecii and its DHPS mutants in China, especially in low endemic areas, are still limited. Thus, in the present study, we measured the P. jirovecii infection rate among HIV-positive and AIDS (HIV/AIDS) patients with suspected PCP and investigated the relationship between CD4+ T cell count and PCP occurrence. As well as the polymerase chain reaction (PCR) analysis and sequencing, the restriction fragment length polymorphism (RFLP) method was used to analyze DHPS point mutation in P. jirovecii strains. P. jirovecii was detected in 40.82% of cases. The clinical symptoms and signs of PCP were not typical; with decreasing CD4+ T cell counts, PCP infection in HIV/AIDS patients increased. In only one case (1.67%), the patients' DHPS gene could not be cut by the Acc I restriction enzyme. Furthermore, mutation at codon 171 was detected in 11 cases and no mutation was found at codon 57. Patients treated with sulfamethoxazole combined with Voriconazole or Caspofungin exhibited favorable results. After treatment, the symptoms of dyspnea were alleviated, and chest computed tomography findings showed the improvement of lung shadows. These indicated that the prevalence of DHPS mutations in P. jirovecii isolates in AIDS-PCP patients in the region was low. Thus, the contribution of gene mutations to treatment failure requires further research.

Immunization with Pneumocystis recombinant KEX1 induces robust and durable humoral responses in immunocompromised non-human primates

Infection with the opportunistic fungal pathogen, Pneumocystis jirovecii causes life-threatening pneumonia in immunocompromised individuals. In addition to HIV-1 infected patients, individuals at risk of Pneumocystis infection include those receiving immunosuppressive therapies due to transplantation, cancer or autoimmune disease. Antibiotic treatment is not always successful, and it does not prevent obstructive lung disease after clearance of the pathogen. Therefore, it is essential to develop therapeutic alternatives that are more effective against PCP. We reported that Pneumocystis recombinant protein KEX1 induces protective immunity against the development of PCP in a non-human primate model of HIV-induced immunosuppression. In this study, we tested the immunogenicity KEX1 immunization of healthy rhesus macaques and the durability of these responses during drug-induced immunosuppression using tacrolimus (FK506) and methylprednisolone. We observed that vaccination with KEX1 prior to the start of the immunosuppressive regimen generated a robust and long-lasting antibody response that was maintained throughout the immunosuppressive treatment. Furthermore, boosting with KEX1 during immunosuppression induced recall of memory responses against recombinant KEX1. The durability of the anti-KEX1 response and the ability to induce a recall response during immunosuppressive therapy provide a proof-of-concept data supporting further investigation of the KEX1 as a prophylactic vaccine to prevent PCP in drug-induced immunosuppression. This approach provides fundamental knowledge for the elaboration of therapeutic and prophylactic alternatives for PCP in patients undergoing severe immunosuppressive therapy.

Pathogenic Fungal Infection in the Lung

Respiratory fungal infection is a severe clinical problem, especially in patients with compromised immune functions. Aspergillus, Cryptococcus, Pneumocystis, and endemic fungi are major pulmonary fungal pathogens that are able to result in life-threatening invasive diseases. Growing data being reported have indicated that multiple cells and molecules orchestrate the host's response to a fungal infection in the lung. Upon fungal challenge, innate myeloid cells including macrophages, dendritic cells (DC), and recruited neutrophils establish the first line of defense through the phagocytosis and secretion of cytokines. Natural killer cells control the fungal expansion in the lung via the direct and indirect killing of invading organisms. Adaptive immune cells including Th1 and Th17 cells confer anti-fungal activity by producing their signature cytokines, interferon-γ, and IL-17. In addition, lung epithelial cells (LEC) also participate in the resistance against fungal infection by internalization, inflammatory cytokine production, or antimicrobial peptide secretion. In the host cells mentioned above, various molecules with distinct functions modulate the immune defense signaling: Pattern recognition receptors (PRRs) such as dectin-1 expressed on the cell surface are involved in fungal recognition; adaptor proteins such as MyD88 and TRAF6 are required for transduction of signals to the nucleus for transcriptional regulation; inflammasomes also play crucial roles in the host's defense against a fungal infection in the lung. Furthermore, transcriptional factors modulate the transcriptions of a series of genes, especially those encoding cytokines and chemokines, which are predominant regulators in the infectious microenvironment, mediating the cellular and molecular immune responses against a fungal infection in the lung.

Pneumocystis infection alters the activation state of pulmonary macrophages

Recent studies show a substantial incidence of Pneumocystis jirovecii colonization and infection in patients with chronic inflammatory lung conditions. However, little is known about the impact of Pneumocystis upon the regulation of pulmonary immunity. We demonstrate here that Pneumocystis polarizes macrophages towards an alternatively activated macrophage-like phenotype. Genetically engineered mice that lack the ability to signal through IL-4 and IL-13 were used to show that Pneumocystis alternative macrophage activation is dependent upon signaling through these cytokines. To determine whether Pneumocystis-induced macrophage polarization would impact subsequent immune responses, we infected mice with Pneumocystis and then challenged them with Pseudomonas aeruginosa 14 days later. In co-infected animals, a higher proportion of macrophages in the alveolar and interstitial spaces expressed both classical and alternatively activated markers and produced the regulatory cytokines TGFβ and IL-10, as well as higher arginase levels than in mice infected with P. aeruginosa alone. Our results suggest that Pneumocystis reprograms the overall macrophage repertoire in the lung to that of a more alternatively-activated setpoint, thereby altering subsequent immune responses. These data may help to explain the association between Pneumocystis infection and decline in pulmonary function.

Vaccine-Induced Immunogenicity and Protection Against Pneumocystis Pneumonia in a Nonhuman Primate Model of HIV and Pneumocystis Coinfection

BACKGROUND

The ubiquitous opportunistic pathogen Pneumocystis jirovecii causes pneumonia in immunocompromised individuals, including human immunodeficiency virus (HIV)-infected individuals, and pulmonary colonization with P. jirovecii is believed to be a cofactor in the development of chronic obstructive pulmonary disease. There is no vaccine for P. jirovecii; however, most adults are seropositive, indicating natural immune priming to this pathogen. We have shown that humoral response to a recombinant subunit of the P. jirovecii protease kexin (KEX1) correlates with protection from P. jirovecii colonization and pneumonia.

METHODS

Here we evaluated the immunogenicity and protective capacity of the recombinant KEX1 peptide vaccine in a preclinical, nonhuman primate model of HIV-induced immunosuppression and Pneumocystis coinfection.

RESULTS

Immunization with KEX1 induced a robust humoral response remained at protective levels despite chronic simian immunodeficiency virus/HIV-induced immunosuppression. KEX1-immunized macaques were protected from Pneumocystis pneumonia, compared with mock-immunized animals (P= .047), following immunosuppression and subsequent natural, airborne exposure to Pneumocystis

CONCLUSIONS

These data support the concept that stimulation of preexisting immunological memory to Pneumocystis with a recombinant KEX1 vaccine prior to immunosuppression induces durable memory responses and protection in the context of chronic, complex immunosuppression.

Pneumocystis jirovecii can be productively cultured in differentiated CuFi-8 airway cells

Although Pneumocystis jirovecii is a well-known and serious pathogen, all previous attempts to isolate, cultivate, and propagate this fungus have failed. This serious challenge in microbiology was addressed in the present study. We examined whether P. jirovecii could be cultured in a permanent three-dimensional air-liquid interface culture system formed by CuFi-8 cells, a differentiated pseudostratified airway epithelial cell line. Cultured pseudostratified cells were inoculated with bronchoalveolar fluid that had been confirmed to be positive for P. jirovecii using PCR. Five days later, the cells and basal medium were harvested and tested for P. jirovecii using quantitative PCR (qPCR), commercially available immunofluorescence detection assays, and Grocott staining of formalin-fixed, paraffin-embedded thin sections of infected-cell cultures. We successfully productively cultivated and propagated P. jirovecii from these P. jirovecii-positive bronchoalveolar lavage fluid (BALF) samples. Furthermore, we provide evidence that P. jirovecii induced cytopathic effects on lung epithelial cells and was even invasive in cell culture. To the best of our knowledge, the cell culture system developed herein represents the first methodology to enable molecular analyses of this pathogen’s life cycle and further in vitro studies of P. jirovecii, such as assessments of drug sensitivity and resistance as well as investigations of the pathogen’s stability against environmental factors and disinfectants.

This is the first report of the successful productive cultivation and propagation of Pneumocystis jirovecii, a human-pathogenic fungus of major clinical significance. These findings are groundbreaking because they will influence the field of diagnostic microbiology, facilitate the testing of antibiotics against P. jirovecii, and enable stability studies of this pathogen when exposed to the environmental factors and chemicals that hospitals are required to use for disinfection. Because productively culturing P. jirovecii has been attempted unsuccessfully for several decades, this study represents a breakthrough in this field.

Trimethoprim-sulfamethoxazole treatment does not reverse obstructive pulmonary changes in pneumocystis-colonized nonhuman primates with SHIV infection

BACKGROUND

Despite antiretroviral therapy and trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis, Pneumocystis pneumonia remains an important serious opportunistic infection in HIV-infected persons. Pneumocystis (Pc) colonization in HIV-infected individuals and in HIV-uninfected smokers is associated with chronic obstructive pulmonary disease (COPD). We previously developed a nonhuman primate model of HIV infection and Pc colonization and demonstrated that Pc colonization correlated with COPD development. In the present study, we examined kinetics of COPD development in non-human primate and tested the effect of Pc burden reduction on pulmonary function by TMP-SMX treatment.

METHODS

Cynomolgus macaques (n = 16) were infected with simian/human immunodeficiency virus (SHIV89.6P), and natural Pc colonization was examined by nested polymerase chain reaction of serial bronchoalveolar lavage fluid and anti-Pc serology.

RESULTS

Eleven of 16 monkeys became Pc colonized by 16 weeks post simian-human immunodeficiency virus (SHIV) infection. Pc colonization of SHIV-infected monkeys led to progressive declines in pulmonary function as early as 4 weeks after Pc detection. SHIV-infected and Pc-negative monkeys maintained normal lung function. At 25 weeks post-SHIV infection, TMP-SMX treatment was initiated in 7 Pc-positive (Pc+) (TMP: 20 mg/kg and SMX: 100 mg/kg, daily for 48 weeks) and 5 Pc-negative (Pc-) monkeys. Four SHIV+/Pc+ remained untreated for the duration of the experiment. Detection frequency of Pc in serial bronchoalveolar lavage fluid (P < 0.001), as well as plasma Pc antibody titers (P = 0.02) were significantly reduced in TMP-SMX-treated macaques compared with untreated.

CONCLUSIONS

Reduction of Pc colonization by TMP-SMX treatment did not improve pulmonary function, supporting the concept that Pc colonization results in early, permanent obstructive changes in the lungs of immunosuppressed macaques.

Modulation of inflammasome-mediated pulmonary immune activation by type I IFNs protects bone marrow homeostasis during systemic responses to Pneumocystis lung infection

Although acquired bone marrow failure (BMF) is considered a T cell-mediated autoimmune disease, possible innate immune defects as a cause for systemic immune deviations in response to otherwise innocuous infections have not been extensively explored. In this regard, we recently demonstrated an important role of type I IFNs in protecting hematopoiesis during systemic stress responses to the opportunistic fungal pathogen Pneumocystis in lymphocyte-deficient mice. Mice deficient in both lymphocytes and type I IFN receptor (IFrag(-/-) mice) develop rapidly progressing BMF due to accelerated bone marrow (BM) cell apoptosis associated with innate immune deviations in the BM in response to Pneumocystis lung infection. However, the communication pathway between lung and BM eliciting the induction of BMF in response to this strictly pulmonary infection has been unclear. In this study, we report that absence of an intact type I IFN system during Pneumocystis lung infection not only causes BMF in lymphocyte-deficient mice but also transient BM stress in lymphocyte-competent mice. This is associated with an exuberant systemic IFN-γ response. IFN-γ neutralization prevented Pneumocystis lung infection-induced BM depression in type I IFN receptor-deficient mice and prolonged neutrophil survival time in BM from IFrag(-/-) mice. IL-1β and upstream regulators of IFN-γ, IL-12, and IL-18 were also upregulated in lung and serum of IFrag(-/-) mice. In conjunction, there was exuberant inflammasome-mediated caspase-1 activation in pulmonary innate immune cells required for processing of IL-18 and IL-1β. Thus, absence of type I IFN signaling during Pneumocystis lung infection may result in deregulation of inflammasome-mediated pulmonary immune activation, causing systemic immune deviations triggering BMF in this model.

Specific detection of Pneumocystis jirovecii in clinical samples by flow cytometry

Pneumocystis jirovecii is an opportunistic pathogen responsible for severe pneumonia in immunocompromised patients. Flow cytometry (FC) is a method widely used in different areas of clinical diagnosis like hematology and immunology. Recently it has started to be used in microbiology with a great potential for diagnosis of emergent microorganisms in clinical samples, especially when present in low numbers. The detection of Pneumocystis jirovecii in respiratory samples can be performed by FC, using specific monoclonal antibodies. Considering clinical diagnosis as a reference method, we previously showed FC to be 100% sensitive and specific when compared to immunofluorescence. Being an automated method, it is faster and less subject to human error than microscopic evaluation.

Colonization by Pneumocystis jirovecii and its role in disease

Although the incidence of Pneumocystis pneumonia (PCP) has decreased since the introduction of combination antiretroviral therapy, it remains an important cause of disease in both HIV-infected and non-HIV-infected immunosuppressed populations. The epidemiology of PCP has shifted over the course of the HIV epidemic both from changes in HIV and PCP treatment and prevention and from changes in critical care medicine. Although less common in non-HIV-infected immunosuppressed patients, PCP is now more frequently seen due to the increasing numbers of organ transplants and development of novel immunotherapies. New diagnostic and treatment modalities are under investigation. The immune response is critical in preventing this disease but also results in lung damage, and future work may offer potential areas for vaccine development or immunomodulatory therapy. Colonization with Pneumocystis is an area of increasing clinical and research interest and may be important in development of lung diseases such as chronic obstructive pulmonary disease. In this review, we discuss current clinical and research topics in the study of Pneumocystis and highlight areas for future research.

Serologic responses to pneumocystis proteins in HIV patients with and without Pneumocystis jirovecii pneumonia

BACKGROUND

Immune responses to Pneumocystis jirovecii are not well understood in HIV infection, but antibody responses to proteins may be useful as a marker of Pneumocystis risk or presence of Pneumocystis pneumonia (PcP).

DESIGN

Retrospective analysis of a prospective cohort.

METHODS

Enzyme-linked immunosorbent assays of antibodies to recombinant Pneumocystis proteins of major surface glycoprotein fragments (MsgC1, C3, C8, and C9) and of antibody titers to recombinant kexin protein (KEX1) were performed on 3 sequential serum samples up to 18 months before and 3 samples after first AIDS-defining illness from Multicenter AIDS Cohort Study participants and compared between those who had PcP or a non-PcP AIDS-defining illness.

RESULTS

Fifty-four participants had PcP and 47 had a non-PcP AIDS-defining illness. IgG levels to MsgC fragments were similar between groups before first AIDS-defining illness, but the PcP group had higher levels of IgG to MsgC9 (median units/mL 50.2 vs. 22.2, P = 0.047) post-illness. Participants with PcP were more likely to have an increase in MsgC3 [odds ratio (OR): 3.9, P = 0.02], MsgC8 (OR: 5.5, P = 0.001), and MsgC9 (OR: 4.0, P = 0.007). The PcP group was more likely to have low KEX1 IgG before development of PcP (OR: 3.6, P = 0.048) independent of CD4 cell count and to have an increase in high IgG titers to KEX1 after PcP.

CONCLUSIONS

HIV-infected individuals develop immune responses to both Msg and kexin proteins after PcP. Low KEX1 IgG titers may be a novel marker of future PcP risk before CD4 cell count has declined below 200 cells per microliter.

Interactions between HIV infection and chronic obstructive pulmonary disease: Clinical and epidemiological aspects

Introduction

An association between HIV infection and chronic obstructive pulmonary disease (COPD) has been observed in several studies.

Objective and methods

we conducted a review of the literature linking HIV infection to COPD, focusing on clinical and epidemiological data published before and during widespread highly active antiretroviral therapy (HAART).

Results

Interactions between HIV infection and COPD appear to be influenced by multiple factors. In particular, the bronchopulmonary tract can be damaged by HIV infection, the immunodeficiency it induces, and the resulting increase in the risk of pulmonary infections. In addition, the prevalence of smoking and intravenous drug use is higher in HIV-infected populations, also increasing the risk of COPD. Before the advent of HAART, respiratory tract infections probably played a major role. Since the late 1990s and the widespread use of HAART, the frequency of opportunistic infections has fallen but new complications have emerged as life expectancy has increased.

Conclusion

given the high prevalence of smoking among HIV-infected patients, COPD may contribute significantly to morbidity and mortality in this setting.

Pneumocystis infection and the pathogenesis of chronic obstructive pulmonary disease

With increases in the immunocompromised patient population and aging of the HIV+ population, the risk of serious fungal infections and their complications will continue to rise. In these populations, infection with the fungal opportunistic pathogen Pneumocystis jirovecii remains a leading cause of morbidity and mortality. Infection with Pneumocystis (Pc) has been shown to be associated with the development of chronic obstructive pulmonary disease (COPD) in human subjects with and without HIV infection and in non-human primate models of HIV infection. In human studies and in a primate model of HIV/Pc co-infection, we have shown that antibody response to the Pc protein, kexin (KEX1), correlates with protection from colonization, Pc pneumonia, and COPD. These findings support the hypothesis that immunity to KEX1 may be critical to controlling Pc colonization and preventing or slowing development of COPD.

Decreased serum antibody responses to recombinant pneumocystis antigens in HIV-infected and uninfected current smokers

Serologic studies can provide important insights into the epidemiology and transmission of Pneumocystis jirovecii. Exposure to P. jirovecii can be assessed by serum antibody responses to recombinant antigens from the major surface glycoprotein (MsgC), although factors that influence the magnitude of the antibody response are incompletely understood. We determined the magnitudes of antibody responses to P. jirovecii in comparison to adenovirus and respiratory syncytial virus (RSV) in HIV-infected and uninfected patients and identified predictors associated with the magnitude of the response. We performed a cross-sectional analysis using serum samples and data from 153 HIV-positive and 92 HIV-negative subjects enrolled in a feasibility study of the Veterans Aging Cohort 5 Site Study (VACS 5). Antibodies were measured using an enzyme-linked immunosorbent assay (ELISA). Independent predictors of antibody responses were determined using multivariate Tobit regression models. The results showed that serum antibody responses to P. jirovecii MsgC fragments were significantly and independently decreased in current smokers. Antibodies to P. jirovecii also tended to be lower with chronic obstructive pulmonary disease (COPD), hazardous alcohol use, injection drug use, and HIV infection, although these results were not statistically significant. These results were specific to P. jirovecii and did not correlate with adenovirus. Antibody responses to RSV were in the inverse direction. Thus, current smoking was independently associated with decreased P. jirovecii antibody responses. Whether smoking exerts an immunosuppressive effect that affects the P. jirovecii antibody response, colonization, or subsequent risk for disease is unclear; prospective, longitudinal studies are needed to evaluate these findings further.

Serum antibody levels to the Pneumocystis jirovecii major surface glycoprotein in the diagnosis of P. jirovecii pneumonia in HIV+ patients

Background

Pneumocystis jirovecii remains an important cause of fatal pneumonia (Pneumocystis pneumonia or PcP) in HIV+ patients and other immunocompromised hosts. Despite many previous attempts, a clinically useful serologic test for P. jirovecii infection has never been developed.

Methods/Principal Findings

We analyzed serum antibody responses to the P. jirovecii major surface glycoprotein recombinant fragment C1 (MsgC1) in 110 HIV+ patients with active PcP (cases) and 63 HIV+ patients with pneumonia due to other causes (controls) by an enzyme-linked immunosorbent assay (ELISA). The cases had significantly higher IgG and IgM antibody levels to MsgC1 than the controls at hospital admission (week 0) and intervals up to at least 1 month thereafter. The sensitivity, specificity and positive predictive value (PPV) of IgG antibody levels increased from 57.2%, 61.7% and 71.5% at week 0 to 63.4%, 100%, and 100%, respectively, at weeks 3–4. The sensitivity, specificity and PPV of IgM antibody levels rose from 59.7%, 61.3%, and 79.3% at week 0 to 74.6%, 73.7%, and 89.8%, respectively, at weeks 3–4. Multivariate analysis revealed that a diagnosis of PcP was the only independent predictor of high IgG and IgM antibody levels to MsgC1. A high LDH level, a nonspecific marker of lung damage, was an independent predictor of low IgG antibody levels to MsgC1.

Conclusions/Significance

The results suggest that the ELISA shows promise as an aid to the diagnosis of PCP in situations where diagnostic procedures cannot be performed. Further studies in other patient populations are needed to better define the usefulness of this serologic test.

Relationship of Pneumocystis jiroveci humoral immunity to prevention of colonization and chronic obstructive pulmonary disease in a primate model of HIV infection

Pulmonary colonization by the opportunistic pathogen Pneumocystis jiroveci is common in HIV(+) subjects and has been associated with development of chronic obstructive pulmonary disease (COPD). Host and environmental factors associated with colonization susceptibility are undefined. Using a simian-human immunodeficiency virus (SHIV) model of HIV infection, the immunologic parameters associated with natural Pneumocystis jiroveci transmission were evaluated. SHIV-infected macaques were exposed to P. jiroveci by cohousing with immunosuppressed, P. jiroveci-colonized macaques in two independent experiments. Serial plasma and bronchoalveolar lavage (BAL) fluid samples were examined for changes in antibody titers to recombinant Pneumocystis-kexin protein (KEX1) and evidence of Pneumocystis colonization by nested PCR of BAL fluid. In experiment 1, 10 of 14 monkeys became Pneumocystis colonized (Pc(+)) by 8 weeks post-SHIV infection, while 4 animals remained Pneumocystis colonization negative (Pc(-)) throughout the study. In experiment 2, 11 of 17 animals became Pneumocystis colonized by 16 weeks post-SHIV infection, while 6 monkeys remained Pc(-). Baseline plasma KEX1-IgG titers were significantly higher in monkeys that remained Pc(-), compared to Pc(+) monkeys, in experiments 1 (P = 0.013) and 2 (P = 0.022). Pc(-) monkeys had greater percentages of Pneumocystis-specific memory B cells after SHIV infection compared to Pc(+) monkeys (P = 0.037). After SHIV infection, Pc(+) monkeys developed progressive obstructive pulmonary disease, whereas Pc(-) monkeys maintained normal lung function throughout the study. These results demonstrate a correlation between the KEX1 humoral response and the prevention of Pneumocystis colonization and obstructive lung disease in the SHIV model. In addition, these results indicate that an effective Pneumocystis-specific memory B-cell response is maintained despite progressive loss of CD4(+) T cells during SHIV infection.

A new method for the detection of Pneumocystis jirovecii using flow cytometry

Pneumocystis jirovecii is an opportunistic pathogen responsible for severe pneumonia in immunocompromised patients. Its diagnosis has been based upon direct microscopy either by classic staining (Gomori Grocott) or by epifluorescence microscopy (immunofluorescence staining, IFS), both of which are time-consuming and low on sensitivity. Our aim was to develop a flow cytometric (FC) protocol for the detection of P. jirovecii on respiratory samples. In our study, 420 respiratory samples were analysed in parallel by IFS and FC, and compared from clinical diagnosis to its resolution upon specific anti-Pneumocystis therapy. The optimum specific antibody concentration for FC analysis was determined to be 10 microg/ml, without any cross-reactions to bacteria or fungi. All positive cases detected by IFS were positive by FC; however, FC classified eight samples to be positive which were classified as negative by routine technique. These samples were obtained from patients with respiratory symptoms who responded favourably to Pneumocystis-specific therapy and were subsequently considered to be true-positives. Using clinical diagnosis as a reference method, FC showed 100% sensitivity and specificity, whereas IFS showed 90.9% sensitivity and 100% specificity. According to our results, a new diagnostic approach is now available to detect P. jirovecii in respiratory samples.

Long-term serologic responses to the Pneumocystis jirovecii major surface glycoprotein in HIV-positive individuals with and without P. jirovecii infection

BACKGROUND

The immune responses to Pneumocystis jirovecii major surface glycoprotein (Msg) in individuals with human immunodeficiency virus (HIV) infection are poorly understood.

METHODS

We examined the sequential serologic responses to recombinant Msg carboxyl terminus fragments (MsgC1, MsgC3, MsgC8, and MsgC9) by enzyme-linked immunosorbent assay in a cohort of individuals with HIV infection for the 5.5 years before death and autopsy. Analyses included mean antibody levels by status at death (Pneumocystis pneumonia, P. jirovecii colonization, or neither), factors associated with high antibody levels, and antibody responses before and after active Pneumocystis pneumonia.

RESULTS

Patients who died from Pneumocystis pneumonia had higher levels of antibody to MsgC8 than did patients who died from other causes. Previous episode of Pneumocystis pneumonia, geographic location, and age were independent predictors of high levels of anitbodies to most or all Msgs. Failure to take Pneumocystis pneumonia prophylaxis was associated with high levels of antibody to MsgC1. Patients who developed and recovered from active Pneumocystis pneumonia during the study exhibited an increase in serum antibody levels that persisted for months after the infection, whereas patients who developed another acquired immunodeficiency syndrome-defining illness did not.

CONCLUSIONS

Serum antibodies to Msgs are important markers of P. jirovecii infection in patients with HIV infection and are influenced by host and environmental factors in complex ways.