Histoplasmosis in patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS): multicenter study of outcomes and factors associated with relapse

Although discontinuation of suppressive antifungal therapy for acquired immunodeficiency syndrome (AIDS)-associated histoplasmosis is accepted for patients with immunologic recovery, there have been no published studies of this approach in clinical practice, and minimal characterization of individuals who relapse with this disease. We performed a multicenter retrospective cohort study to determine the outcome in AIDS patients following discontinuation of suppressive antifungal therapy for histoplasmosis. Ninety-seven patients were divided into a physician-discontinued suppressive therapy group (PD) (38 patients) and a physician-continued suppressive therapy group (PC) (59 patients). The 2 groups were not statistically different at baseline, but at discontinuation of therapy and at the most recent follow-up there were significant differences in adherence to therapy, human immunodeficiency virus (HIV) RNA, and urinary Histoplasma antigen concentration. There was no relapse or death attributed to histoplasmosis in the PD group compared with 36% relapse (p < 0.0001) and 5% death (p = 0.28) in the PC group. Relapse occurred in 53% of the nonadherent patients but not in the adherent patients (p < 0.0001). Sixty-seven percent of patients with initial central nervous system (CNS) histoplasmosis relapsed compared to 15% of patients without CNS involvement (p = 0.0004), which may be accounted for by nonadherence. In addition, patients with antigenuria above 2.0 ng/mL at 1-year follow-up were 12.82 times (95% confidence interval, 2.91-55.56) more likely to relapse compared to those with antigenuria below 2.0 ng/mL. Discontinuation of antifungal therapy was safe in adherent patients who completed at least 1 year of antifungal treatment, and had CD4 counts >150 cells/mL, HIV RNA <400 c/mL, Histoplasma antigenuria <2 ng/mL (equivalent to <4.0 units in second-generation method), and no CNS histoplasmosis.

B cells and CD4-CD8- T cells are key regulators of the severity of reactivation histoplasmosis

The fungus, Histoplasma capsulatum, produces a persistent infection. Reactivation histoplasmosis is largely a result of impaired immunity, but the perturbations associated with escape of the fungus from host defenses remain ill-defined. We analyzed a murine model of reactivation to elucidate the host defects that permit reactivation. C57BL/6 mice were infected intranasally and, 42 days later, they were depleted of CD4(+) and CD8(+) cells. Elimination of these cells, but not either alone, produced a persistent infection over several weeks. Neutralization of IFN-gamma, TNF-alpha, or both did not induce reactivation. Endogenous IL-10 exacerbated reactivation. Depletion of T cells in B cell(-/-) mice induced a markedly higher burden in organs when compared with wild type. However, the infection remained persistent. Elimination of CD4(+) cells alone or neutralization of cytokines increased the fungal load. The persistent infection was not dependent on gammadelta T cells or NK cells. Elimination of Thy-1.2(+) cells in mice given mAb to CD4 and CD8 transformed reactivation into a progressive, lethal infection in B cell(-/-) and wild-type mice, but the tempo of progression was accelerated in the former. The data reveal the complex control by the host to prevent reactivation of this fungus.

Pulmonary V beta 4+ T cells from Histoplasma capsulatum-infected mice respond to a homologue of Sec31 that confers a protective response

The population of V beta 4+ T cells expands in the lungs of C57BL/6 mice infected with Histoplasma capsulatum, and the elimination of these cells impairs protective immunity. To determine the antigen or antigens that trigger their proliferation, V beta 4+ T cell hybridomas were generated from the lungs and spleens of infected mice. We mapped the antigenic determinants by T cell Western blot. Pulmonary and splenic T cells recognized 3 regions comprising <25, 55-70, and 125-140 kDa. The majority of hybridomas from lungs, but not from spleens, responded to the high molecular mass region. A protein from that area was identified, by amino acid sequencing, as a homologue of Sec31 from Saccharomyces cerevisiae. Vaccination with recombinant Sec31 reduced fungal burden and improved survival in mice, and its efficacy was critically dependent on the presence of V beta 4+ T cells. Thus, a homologue of Sec31 is a trigger of the expansion of the V beta 4+ T cell population and is important to the generation of protective immunity.

Preventing reactivation of ocular histoplasmosis: Guidance for patients at risk

BACKGROUND

Ocular histoplasmosis syndrome (OHS), a significant cause of vision loss in young and middle-aged adults, is associated with the fungus Histoplasma capsulatum (Hc). There is considerable evidence that recurrent reactivation of perimacular ocular histoplasmosis lesions is an important cause of disease progression and that vision loss is at least, in part, a consequence of host sensitivity to fungal antigen.

METHODS

The etiology and pathogenesis of OHS is reviewed and specific recommendations are made for patients with OHS that may decrease the risk of reactivation of ocular histoplasmosis lesions and slow disease progression.

CONCLUSION

Patients with perimacular chorioretinal scars secondary to OHS should be informed by the clinician that they are at risk for vision loss; they should be told the symptoms of choroidal neovascularization and how to self-monitor their vision with an Amsler grid. We recommend they also be instructed on how to decrease their risk of reinfection by Hc. Aggressive treatment of dermatomycoses, onychomycosis, vaginal candidiasis, and other chronic fungal infections may decrease the risk of reactivation of ocular lesions. Patients with OHS who are considering LASIK surgery should be informed that the procedure may trigger choroidal neovascularization.

Progress in vaccination for histoplasmosis and blastomycosis: coping with cellular immunity

Human infection with Histoplasma capsulatum or Blastomyces dermatitidis is sufficiently frequent to warrant exploring the development of vaccines. This review examines the advancements that have been accomplished over the last few years. The availability of molecular tools to create recombinant antigens or mutant strains has produced a small number of useful vaccine candidates. More importantly, the studies summarized herein demonstrate that understanding the host response to a protein or mutant fungus is critical to creating a vaccine that may be useful for the immunocompromised patient.

Protective Antibodies and Endemic Dimorphic Fungi

The host response to infection is the outcome of a complex interaction between a microbe and a host's innate and adaptive immune system. In this context, the role of antibody in the endemic mycoses is relatively poorly understood. Recently, a monoclonal antibody to a cell surface protein has been shown to be protective in a murine histoplasmosis model. The findings with Histoplasma capsulatum may provide a paradigm for antibody protection against endemic fungi. This paper reviews the recent data on protective antibody in histoplasmosis and previous data supporting a role for antibody in protective responses in other dimorphic fungi.

Efficacy of cell-free antigens in evaluating cell immunity and inducing protection in a murine model of histoplasmosis

Histoplasma capsulatum is a dimorphic pathogenic fungus that causes a wide spectrum of disease when mycelial fragments are inhaled. Resistance to H. capsulatum is dependent on cellular immunity mediated by T cells and macrophages. Here we standardized the production of extracts containing cell-free antigens (CFAgs) and observed their efficacy in evaluating cellular immunity during murine histoplasmosis. CFAgs induced a more potent delayed-type hypersensitivity (DTH) response in H. capsulatum-infected mice than did histoplasmin-a classical antigen. This DTH response to CFAgs is able to determine the immune status of infected mice and to predict their death. Moreover, CFAgs stimulated spleen cells from immune mice to produce higher amounts of gamma interferon (IFN-gamma) in vitro. Finally, immunization with CFAgs protected against a lethal inoculum of H. capsulatum. These results demonstrate that CFAgs may be useful for the evaluation of cellular immune response and as a potential source for the development of a vaccine against histoplasmosis.

Successful discontinuation of secondary prophylaxis for histoplasmosis after highly active antiretroviral therapy

Whether maintenance antifungal prophylaxis against histoplasmosis should be continued life-long in patients with immune restoration after highly active antiretroviral therapy (HAART) remains unclear. We report a case of disseminated histoplasmosis involving the skin, lung, gastrointestinal tract, mesentery, and retroperitoneum in a 33-year-old man with acquired immunodeficiency syndrome. His symptoms improved after use of amphotericin B and itraconazole in addition to ileostomy to relieve the intestinal obstruction. After the start of HAART, he was able to discontinue itraconazole as maintenance therapy without relapse for 24 months.

[Interruption of antifungal secondary prophylaxis in AIDS-related histoplasmosis]

The clinical data of 21 patients, suffering AIDS-related histoplasmosis, who were able to interrupt antifungal secondary prophylaxis, after achieving a partial restoration of the cell mediated immunity by HAART administration, are presented. They were 16 males and five females, whose ages varied between 32 and 54 years (mean = 38.5 years). All of them presented disseminated progressive forms of histoplasmosis, with multiple locations (skin, mucous membranes, liver, spleen, lymph nodes and lungs). The majority of the cases suffered other concomitant diseases (specially tuberculosis and Kaposi sarcoma), 66.6 % of the patients had less than 50 CD4+ cells/microl at the start of treatment and the average viral burden was 278,385 RNA copies/ml. The initial treatment consisted in 400 mg/day of itraconazole, by oral route, in 14 cases and the remaining seven patients were treated with amphotericin B, intravenously, at a daily dose of 0.7 mg/kg of body weight. One patient who did not tolerate amphotericin B and presented a partial response to itraconazole, was treated with posaconazole orally at a daily dose of 800 mg. Fourteen patients received oral itraconazole at a daily dose of 200 mg as a secondary prophylaxis, the remaining three patients were treated with intravenous amphotericin B, 50 mg twice a week. After HAART for an average lapse of 16.7 months (10 to 32 months), five cases showed CD4+ cells counts above 150 cells/microl and the remaining 16 presented more than 200 cells/microl; 18 of them had undetectable viral burden and all cases were asymptomatic. The follow up after secondary prophylaxis discontinuation varied between six months and six years (mean= 33.6 months). Twenty out of 21 patients (95 %) were clinically stable, without any manifestation of relapses, including two patients who abandoned HAART. One patient, who discontinued HAART, contracted a fatal bacterial pneumonia. Even though the limited number of cases, the data presented in this study seem to suggest that it is possible to interrupt antifungal secondary prophylaxis of histoplasmosis, when the patient is clinically asymptomatic and the CD4+ cells counts are above 150 cells/microl.

Safety of Discontinuation of Maintenance Therapy for Disseminated Histoplasmosis after Immunologic Response to Antiretroviral Therapy

We performed a prospective observational study to assess the safety of stopping maintenance therapy for disseminated histoplasmosis among human immunodeficiency virus infected patients after response to antiretroviral therapy. All subjects received at least 12 months of antifungal therapy and 6 months of antiretroviral therapy before entry. Negative results of fungal blood cultures, urine and serum Histoplasma antigen level of <4.1 units, and CD4+ T cell count of >150 cells/mm3 were required for eligibility. Thirty-two subjects were enrolled; the median CD4+ T cell count at study entry was 289 cells/mm3. No relapses of histoplasmosis occurred after a median duration of follow-up of 24 months. This corresponded to an observed relapse rate of 0 cases per 65 person-years. The median CD4+ T cell count at final study visit was 338 cells/mm3. Discontinuation of antifungal maintenance therapy appears to be safe for patients with acquired immunodeficiency syndrome with previously treated disseminated histoplasmosis and sustained immunologic improvement in response to antiretroviral therapy.

Histoplasmosis in Two Human Immunodeficiency Virus-positive Immigrants to Italy: Clinical Features and Management in the Highly Active Antiretroviral Therapy Era

We report two cases of histoplasmosis occurring in human immunodeficiency virus-positive patients who immigrated to Italy, and focus our attention on the clinical features and therapeutic aspects, with particular emphasis on secondary prophylaxis. The patients had comparable human immunodeficiency virus baseline parameters, but had a completely different compliance over therapeutic regimens. The two patients were followed in two different city hospitals of our region, Padua and Verona, and the diagnosis was made on the basis of instrumental, histologic, and microbiologic findings. One of them was treated with corticosteroids because of nephrotic syndrome.

Protective and memory immunity to Histoplasma capsulatum in the absence of IL-10

We determined whether the absence of IL-10 in mice influenced protective and memory immunity to Histoplasma capsulatum. IL-10(-/-) mice cleared primary and secondary infection more rapidly than wild-type controls. Administration of mAb to TNF-alpha or IFN-gamma, but not GM-CSF, abrogated protection in naive IL-10(-/-) mice; mAb to TNF-alpha, but not IFN-gamma or GM-CSF, subverted protective immunity in secondary histoplasmosis. The inflammatory cell composition in IL-10(-/-) mice was altered in those given mAb to IFN-gamma or TNF-alpha. More Gr-1(+) and Mac-3(+) cells were present in lungs of IL-10(-/-) mice given mAb to IFN-gamma, and treatment with mAb to TNF-alpha sharply reduced the number of CD8(+) cells in lungs of IL-10(-/-) mice. We ascertained whether the lack of IL-10 modulated memory T cell generation or the protective function of cells. The percentage of CD3(+), CD44(high), CD62(low), and IFN-gamma(+) cells in IL-10(-/-) mice was higher than that of wild-type at day 7 but not day 21 or 49 after immunization. Fewer splenocytes from immunized IL-10(-/-) mice were required to mediate protection upon adoptive transfer into infected TCR alphabeta(-/-) mice. Hence, deficiency of IL-10 confers a salutary effect on the course of histoplasmosis, and the beneficial effects of IL-10 deficiency require endogenous TNF-alpha and/or IFN-gamma. Memory cell generation was transiently increased in IL-10(-/-) mice, but the protective function conferred by cells from these mice following immunization is strikingly more vigorous than that of wild-type.

Mucosal and Systemic Fungal Infections in Patients with AIDS

In countries where highly active antiretroviral therapy (HAART) is widely available, a decrease in the incidence of fungal infections has been observed in the last 5 years compared with countries that cannot afford this treatment. Even refractory fungal infections may be controlled when HAART is given to patients, and end-stage AIDS infections, such as aspergillosis, are now only infrequently seen. In contrast, fungal infections in certain regions, such as penicilliosis in Southeast Asia or cryptococcosis in Sub-Saharan Africa, are a growing problem. Antifungal therapy for documented infections has not changed very much during recent years; however, new drugs such as caspofungin and voriconazole may be more effective in the treatment of opportunistic fungal infections, in particular, those involving resistant organisms. Secondary antifungal prophylaxis for many opportunistic pathogens can now be temporarily or even permanently discontinued in many HIV-positive patients who have a marked improvement in immune function parameters, such as CD4(+) cell counts, after initiation of HAART. The link between effective virustatic control of HIV infection and a decreasing incidence of fungal infections has been recognised; and so, despite the availability of very effective new antifungal drugs, the cornerstone of treatment and prevention of opportunistic fungal infections in patients with HIV infection is effective antiretroviral therapy including protease inhibitors.

Antibodies to a cell surface histone-like protein protect against Histoplasma capsulatum

A protective role for antibodies has not previously been described for host defense against the pathogenic fungus Histoplasma capsulatum (Hc). Mouse mAb's were generated from mice immunized with Hc yeast that binds the cell surface of Hc. Administration of mAb's before Hc infection reduced fungal burden, decreased pulmonary inflammation, and prolonged survival in a murine infection model. Protection mediated by mAb's was associated with enhanced levels of IL-4, IL-6, and IFN-gamma in the lungs of infected mice. The mAb's increased phagocytosis of yeast by J774.16 cells through a CR3-dependent process. Ingestion of mAb-opsonized Hc by J774.16 macrophage-like cells was associated with yeast cell growth inhibition and killing. The mAb's bound to a 17-kDa antigen expressed on the surface of Hc. The antigen was identified as a histone H2B-like protein. This study establishes that mAb's to a cell surface protein of Hc alter the intracellular fate of the fungus and mediate protection in a murine model of lethal histoplasmosis, and it suggests a new candidate antigen for vaccine development.

Vaccine immunity to pathogenic fungi overcomes the requirement for CD4 help in exogenous antigen presentation to CD8+ T cells: implications for vaccine development in immune-deficient hosts

Systemic fungal infections with primary and opportunistic pathogens have become increasingly common and represent a growing health menace in patients with AIDS and other immune deficiencies. T lymphocyte immunity, in particular the CD4+ Th 1 cells, is considered the main defense against these pathogens, and their absence is associated with increased susceptibility. It would seem illogical then to propose vaccinating these vulnerable patients against fungal infections. We report here that CD4+ T cells are dispensable for vaccine-induced resistance against experimental fungal pulmonary infections with two agents, Blastomyces dermatitidis an extracellular pathogen, and Histoplasma capsulatum a facultative intracellular pathogen. In the absence of T helper cells, exogenous fungal antigens activated memory CD8+ cells in a major histocompatibility complex class I-restricted manner and CD8+ T cell-derived cytokines tumor necrosis factor alpha, interferon gamma, and granulocyte/macrophage colony-stimulating factor-mediated durable vaccine immunity. CD8+ T cells could also rely on alternate mechanisms for robust vaccine immunity, in the absence of some of these factors. Our results demonstrate an unexpected plasticity of immunity in compromised hosts at both the cellular and molecular level and point to the feasibility of developing vaccines against invasive fungal infections in patients with severe immune deficiencies, including those with few or no CD4+ T cells.

Histoplasmosis

The diagnosis of histoplasmosis depends on recognition of the different clinical manifestations of infection, accompanied by knowledge of the accuracy and limitations of tests used for diagnosis of fungal infections. Although most infections are asymptomatic, histoplasmosis can be severe, or even fatal, in patients who have experienced a heavy exposure, have underlying immune defects, or develop progressive disease that is not recognized and treated. This article provides an up-to-date clinical review of histoplasmosis, focusing on recognition, diagnosis, and management.

The protective immune response to heat shock protein 60 of Histoplasma capsulatum is mediated by a subset of V beta 8.1/8.2+ T cells

Immunization with recombinant heat shock protein 60 (rHsp60) from Histoplasma capsulatum or a region of the protein designated fragment 3 (F3) confers protection from a subsequent challenge in mice. To determine the T cell repertoire involved in the response to Hsp60, T cell clones from C57BL/6 mice immunized with rHsp60 were generated and examined for Vbeta usage by flow cytometry and RT-PCR. Vbeta8.1/8.2(+) T cells were preferentially expanded; other clones bore Vbeta4, -6, or -11. When Vbeta8.1/8.2(+) cells were depleted in mice, Vbeta4(+) T cell clones were almost exclusively isolated. Measurement of cytokine production demonstrated that nine of 16 Vbeta8.1/8.2(+) clones were Th1, while only three of 13 non-Vbeta8.1/8.2(+) clones were Th1. In mice immunized with rHsp60, depletion of Vbeta8.1/8.2(+), but not Vbeta6(+) plus Vbeta7(+), T cells completely abolished the protective efficacy of Hsp60 to lethal and sublethal challenges. Examination of the TCR revealed that a subset of Vbeta8.1/2(+) clones that produced IFN-gamma and were reactive to F3 shared a common CDR3 sequence, DGGQG. Transfer of these T cell clones into TCR alpha/beta(-/-) or IFN-gamma(-/-) mice significantly improved survival, while transfer of other Vbeta8.1/8.2(+) clones that were F3 reactive but were Th2 or clones that were not reactive to F3 but were Th1 did not confer protection. These data indicate that a distinct subset of Vbeta8.1/8.2(+) T cells is crucial for the generation of a protective response to rHsp60.

V beta 6+ T cells are obligatory for vaccine-induced immunity to Histoplasma capsulatum

We examined TCR usage to a protective fragment of heat shock protein 60 from the fungus, Histoplasma capsulatum. Nearly 90% of T cell clones from C57BL/6 mice vaccinated with this protein were Vbeta6+; the remainder were Vbeta14+. Amino acid motifs of the CDR3 region from Vbeta6+ cells were predominantly IxGGG, IGG, or SxxGG, whereas it was uniformly SFSGG for Vbeta14+ clones. Short term T cell lines from Vbeta6+-depleted mice failed to recognize Ag, and no T cell clones could be generated. To determine whether Vbeta6+ cells were functionally important, we eliminated them during vaccination. Depletion of Vbeta6+ cells abrogated protection in vivo and upon adoptive transfer of cells into TCR alphabeta(-/-) mice. Transfer of a Vbeta6+, but not a Vbeta14+, clone into TCR alphabeta(-/-) mice prolonged survival. Cytokine generation by Ag-stimulated splenocytes from immunized mice depleted of Vbeta6+ cells was similar to that of controls. The efficacy of the Vbeta6+ clone was associated with elevated production of IFN-gamma, TNF-alpha, and GM-CSF compared with that of the Vbeta14+ clone. More Vbeta6+ cells were present in lungs and spleens of TCR alphabeta(-/-) on day 3 postinfection compared with Vbeta14+ cells. Thus, a single Vbeta family was essential for vaccine-induced immunity. Moreover, the mechanism by which Vbeta6+ contributed to protective immunity differed between unfractionated splenocytes and T cell clones.

The epidemiology of histoplasmosis: a review

Histoplasmosis is the most common endemic mycosis in the United States and has recently emerged as an important opportunistic infection among human immunodeficiency virus (HIV)-infected persons living in areas where it is endemic. In this article, we describe the epidemiologic and ecologic features of histoplasmosis, highlighting the implications for prevention. Surveillance and education of the public and health care providers are needed to determine the disease burden of histoplasmosis. Development of better diagnostic tests for detection of disease in humans and of the organism in the environment will help in designing better prevention strategies.

Mediastinal fibrosis

Mediastinal fibrosis is the least common, but the most severe, late complication of histoplasmosis. It should be differentiated from the many other less-severe mediastinal complications of histoplasmosis, and from other causes of mediastinal fibrosis. Posthistoplasmosis mediastinal fibrosis is characterized by invasive, calcified fibrosis centered on lymph nodes, which, by definition, occludes major vessels or airways.

Protective efficacy of H antigen from Histoplasma capsulatum in a murine model of pulmonary histoplasmosis

We previously reported that immunization with H antigen from Histoplasma capsulatum did not protect mice against an intravenous challenge with yeasts. Here, we investigated the utility of H antigen to protect mice in a model of pulmonary histoplasmosis. Mice immunized with H antigen and challenged intranasally 4 weeks postvaccination were protected against sublethal and lethal challenges with H. capsulatum yeasts. If the challenge was performed 3 months after vaccination, there was a reduction in fungal burden following sublethal challenge and a modest delay in mortality in mice given a lethal inoculum. Vaccination was associated with production of gamma interferon, granulocyte-macrophage colony-stimulating factor, interleukin-4, and interleukin-10 by splenocytes. Vaccination with H antigen was not accompanied by a major expansion of CD4(+) or CD8(+) cells in spleens of mice. These results demonstrate that H antigen may be useful as a protective immunogen against pulmonary exposure to H. capsulatum.

Multicenter case-control study of risk factors for histoplasmosis in human immunodeficiency virus-infected persons

We conducted a multicenter case-control study to identify risk factors for histoplasmosis among persons with acquired immunodeficiency syndrome (AIDS) and to evaluate predictors of a poor outcome (defined as death or admission to the intensive care unit). Patients with histoplasmosis were each matched by age, sex, and CD4 lymphocyte count to 3 controls. From 1996 through 1999, 92 case patients and 252 controls were enrolled. Of the case patients, 81 (89%) were men, 50 (55%) were black, 78 (85%) had a CD4 lymphocyte count of <100 cells/microL, 80 (87%) were hospitalized, and 11 (12%) died. Multivariable analysis found that receipt of antiretroviral therapy and of triazole drugs were independently associated with a decreased risk of histoplasmosis. Chronic medical conditions and a history of infections with herpes simplex virus were associated with poor outcome. Triazoles should be considered for chemoprophylaxis for persons with AIDS, especially those who take part in high-risk activities that involve frequent exposure to soil, who have CD4 lymphocyte counts of <100 cells/microL, and who live in areas where histoplasmosis is endemic.

V beta 6+ and V beta 4+ T cells exert cooperative activity in clearance of secondary infection with Histoplasma capsulatum

We previously studied the lung Vbeta TCR repertoire of C57BL/6 mice during primary infection with the pathogen Histoplasma capsulatum. We observed a consistent oligoclonal expansion of Vbeta4(+) T cells during the peak of infection and early stages of resolution. The Vbeta4(+) family played a role in protective immunity against the fungus. Depletion of this subpopulation of T cells hindered optimal clearance of infection from tissues. In this report we analyze the flux of the Vbeta TCR repertoire in the lungs of C57BL/6 mice with reinfection histoplasmosis. We observed a significant increase in Vbeta6(+) T cells on days 7, 10, and 14, the peak and early resolution phases of infection. This skewing was preceded by an increased number of memory T cells within Vbeta6(+) cells. The VDJ sequences of Vbeta6 chains were oligoclonal during the early stages of the infection, suggesting that the expansion was driven by a small number of Ags. More than 96% of the expanded Vbeta6(+) cells were CD4(+). Depletion of Vbeta6(+) T cells but not Vbeta4(+) T cells induced a modest but significant delay in fungal clearance. Simultaneous depletion of Vbeta4(+) and Vbeta6(+) T cells induced a more pronounced impairment of host resistance. These studies illustrate the dynamic interactions between Vbeta families in the response to microbial challenge.

Perforin is required for primary immunity to Histoplasma capsulatum

Protective immunity against primary and secondary infection by the fungus Histoplasma capsulatum (HC) is multifactorial, requiring cells of the innate and adaptive immune response. Effector mechanisms that could mediate intracellular killing of HC include cytokines such as IFN-gamma and TNF-alpha and/or direct cytolytic activity by T and NK cells. In this regard, although previous work has clearly demonstrated a critical role for IFN-gamma and TNF-alpha in limiting fungal growth in primary HC infection, less is known regarding the role of cytolytic mechanisms. The studies reported here first address the role of perforin in mediating immunity to HC. Remarkably, perforin-deficient knockout (PfKO) mice were shown to have accelerated mortality and increased fungal burden following a lethal or sublethal primary challenge. These data established an essential role for perforin in primary immunity systemic HC infection. Interestingly, depletion of CD8(+) T cells in PfKO mice caused a further increase in fungal burden and accelerated mortality, suggesting a perforin-independent role for CD8(+) T cells. Moreover, adoptive transfer of CD8(+) T cells from PfKO mice into IFN-gamma(-/-) mice caused a reduction in fungal burden following infectious challenge compared with control IFN-gamma(-/-) mice. Together, these data suggest that CD8(+) T cells can mediate immunity to HC through both perforin-dependent and -independent mechanisms.

Recombinant murine granulocyte-macrophage colony-stimulating factor modulates the course of pulmonary histoplasmosis in immunocompetent and immunodeficient mice

Several endogenous cytokines, including granulocyte-macrophage colony-stimulating factor (GM-CSF), are necessary for eliminating Histoplasma capsulatum from tissues. In this study, we explored the efficacy of recombinant murine GM-CSF in the treatment of pulmonary histoplasmosis. This cytokine significantly reduced fungal burden in a dose-dependent manner. Pretreatment did not consistently produce a better result than treatment started after infection. The biological effectiveness of GM-CSF was not associated with modulation of lung cytokine production or alteration in lung inflammation, but it directly activated a nonadherent lung cell population to exert anti-Histoplasma activity. GM-CSF improved survival of T-cell-depleted mice exposed to H. capsulatum. When combined with a suboptimal amount of amphotericin B, GM-CSF enhanced survival of normal or T-cell-depleted mice given a lethal challenge. These results suggest that this cytokine may be useful as an adjunctive treatment for histoplasmosis.

Single-dose AmBisome (Liposomal amphotericin B) as prophylaxis for murine systemic candidiasis and histoplasmosis

AmBisome is a liposomal formulation of amphotericin B that has broad-spectrum antifungal activity and greatly reduced toxicity compared to the parent drug. In this study, amphotericin B deoxycholate (Fungizone) (1 mg/kg) and AmBisome (1 to 20 mg/kg) were tested as single-dose prophylactic agents in both immunocompetent and immunosuppressed C57BL/6 mice challenged with either Candida albicans or Histoplasma capsulatum. Prophylactic efficacy was based on survival and fungal burden in the target organ (kidneys or spleen). At 9 to 10 days after histoplasma challenge, 80 to 90% of both immunocompetent and immunosuppressed mice in the control and Fungizone groups had died. All AmBisome-treated mice survived, although in the AmBisome groups given 1 mg/kg, the mice became moribund by day 10 to 12. No spleen CFU were detected in the histoplasma-challenged mice given 10 or 20 mg of AmBisome per kg. By 23 to 24 days after histoplasma challenge, fungal growth and/or death had occurred in all immunosuppressed mice except for four mice receiving 20 mg of AmBisome per kg. There were still no detectable fungi in the spleens of immunocompetent mice given 10 or 20 mg of AmBisome per kg. In the C. albicans experiment at 7 days postchallenge, all animals in both untreated and treated groups were alive with culture-positive kidneys. The kidney fungal burdens in AmBisome groups given 5 to 20 mg/kg were at least 1 log unit lower than those in the Fungizone group and significantly lower than those in the untreated control group (P < 0.05). There was a trend toward decreasing fungal growth in the kidneys as the dose of AmBisome was increased. In conclusion, these results show that a single high dose of AmBisome (5 to 20 mg/kg) had prophylactic efficacy in immunocompetent and immunosuppressed murine H. capsulatum and C. albicans models.

Neutralization of endogenous granulocyte-macrophage colony-stimulating factor subverts the protective immune response to Histoplasma capsulatum

We examined the influence of endogenous GM-CSF on the course of primary and secondary pulmonary histoplasmosis. A high proportion (>/=75%) of C57BL/6 mice given mAb to GM-CSF did not survive primary infection, whereas 88-94% of infected controls survived. Analysis of leukocytes revealed significantly fewer CD4+ and CD8+ cells in lungs, but not airways, of anti-GM-CSF-treated mice as compared with infected controls. However, the histopathology was similar between the two groups. Lungs of mice given mAb to GM-CSF manifested depressed levels of TNF-alpha, IFN-gamma, and reactive nitrogen intermediates and elevated levels of IL-4 and IL-10. Administration of mAb to IL-4, to IL-10, or both restored protective immunity in GM-CSF-neutralized mice. In secondary infection, administration of mAb to GM-CSF exacerbated infection but did not alter survival over 30 days. The character of the inflammatory response was similar, and no differences were detected in Th1 or Th2 cytokine production between the two groups. Thus, endogenous GM-CSF is essential for survival in primary but not secondary infection, and blockade perturbs protective immunity. These findings reveal a new mechanism whereby GM-CSF contributes to host protection and demonstrate differences in control of primary and secondary histoplasmosis.

CD40 ligand is not essential for induction of type 1 cytokine responses or protective immunity after primary or secondary infection with histoplasma capsulatum

The induction of type 1 immune responses (interleukin [IL]-12, interferon [IFN]-gamma) has been shown to be important in mediating protection against many intracellular infections including Histoplasma capsulatum. Costimulatory molecules such as CD40 ligand (CD40L) have been shown to be a central regulator of type 1 responses in vivo. To study the role of CD40L in mediating protection against infection with H. capsulatum, CD40L-deficient (CD40L-/-) and CD40L+/+ mice were infected with H. capsulatum and assessed for various parameters. After a lethal challenge of H. capsulatum, CD40L-/- mice were not substantially different from CD40L+/+ mice in terms of mortality, fungal burden, or production of IFN-gamma, IL-12, nitric oxide, or tumor necrosis factor alpha. Moreover, CD40L-/- mice treated with anti-IFN-gamma or anti-IL-12 at the time of infection had accelerated mortality, providing further evidence that IL-12 and IFN-gamma are produced in vivo in the absence of CD40L. In addition, CD40L-/- mice infected with a sublethal dose of H. capsulatum survived infection, whereas all mice infected with the same dose and treated with anti-IFN-gamma had accelerated mortality, demonstrating that IFN-gamma but not CD40L was essential for primary immunity to H. capsulatum infection. Interestingly, depletion of either CD4+ or CD8+ T cells resulted in accelerated mortality in CD40L-/- mice, suggesting a critical role for these cells in response to infection. Finally, CD40L-/- mice initially infected with a sublethal dose of H. capsulatum were protected from secondary infection with a lethal dose of H. capsulatum, demonstrating that CD40L is not required for the maintenance of memory immunity.

Activation of human macrophage fungistatic activity against Histoplasma capsulatum upon adherence to type 1 collagen matrices

Human monocyte/macrophages (Mphi) were adhered to extracellular matrix proteins, and the intracellular growth of Histoplasma capsulatum (Hc) yeasts were quantified and compared with their growth in Mphi adhered to plastic. Freshly isolated monocytes and cultured monocyte/derived Mphi adhered to type 1 collagen gels, but not to nongelled collagen-, fibronectin-, laminin-, or vitronectin-coated surfaces, demonstrated significant fungistatic activity against Hc yeasts. Activation of Mphi developed immediately upon adherence to the collagen matrices (1 h) and did not require additional time in culture. In addition, many of the yeasts were digested by 24 h postinfection. Mphi adhered to collagen maintained their fungistatic activity for up to 4 days, during which time monolayers cultured on plastic were destroyed. Culture of Mphi in the presence of IFN-gamma or TNF-alpha for 24 h before infection did not augment the fungistatic activity of collagen-adherent Mphi. Likewise, culture of monocytes on collagen gels with IL-3, granulocyte-Mphi CSF (GM-CSF) or Mphi CSF (M-CSF) for 7 days did not enhance Mphi fungistatic activity above that obtained by monocytes cultured on collagen alone. The mechanism(s) of Mphi-mediated fungistasis was not associated with production of toxic oxygen radicals, nitric oxide, or the restriction of intracellular iron. However, experiments with horseradish peroxidase-labeled gold colloids and immunoelectron microscopy demonstrated that phagolysosomal fusion, which is minimal in Hc-infected Mphi adhered to plastic, is enhanced significantly at both 1 h and 24 h postinfection in Mphi adhered to collagen matrices. These data suggest that in vivo, matrix-bound Mphi may express a previously unrecognized antifungal activity that proceeds in the absence of exogenous cytokines and is mediated, in part, by overcoming the capacity of Hc yeasts to inhibit Mphi phagolysosomal fusion.

Opportunistic fungal infections in patients with HIV disease: combating cryptococcosis and histoplasmosis

Both cryptococcosis and histoplasmosis are life-threatening diseases in patients with advanced HIV infection. Cryptococcal disease in patients with AIDS is usually a systemic illness with an insidious onset of meningoencephalitis. Development of potent oral antifungal agents has simplified therapy, although patients with cryptococcal meningitis are at high risk for relapse. Histoplasmosis is usually disseminated in AIDS patients. Definitive diagnosis requires culture of the pathogen from blood or other specimens. Although availability of azole compounds has broadened treatment options, relapse is common after treatment of acute disease, and lifelong suppressive oral therapy is needed. Antifungal prophylaxis is not considered cost-effective at this time.

Disseminated histoplasmosis in persons infected with human immunodeficiency virus

Disseminated histoplasmosis is an AIDS-defining illness that occurs in about 5% of AIDS patients residing in histoplasmosis-endemic areas of the United States (the Mississippi and Ohio river valleys). This disease develops as a result of acute infection and perhaps also as the result of reactivation of latent infection: cases reported from areas such as New York City, where histoplasmosis is not endemic, are most likely due to reactivation of an infection acquired earlier in a histoplasmosis-endemic area, while cases in histoplasmosis-endemic areas are most likely due to acute infection, especially in outbreak settings. Disseminated histoplasmosis in HIV-infected patients is usually associated with advanced immunosuppression, with CD4+ lymphocyte counts of < 75/mm3. Currently, histoplasmin skin testing of HIV-infected patients does not seem to be useful in detecting previous exposure and therefore is not helpful in identifying groups of patients who are at risk for dissemination and who should be targeted for preventive efforts. The current public health recommendation for HIV-infected patients is to avoid exposure to sites likely to harbor high levels of Histoplasma capsulatum, such as chicken coops and bird roosts. The role of chemoprophylaxis is not clear, but an ongoing study by the Mycoses Study Group is evaluating the role of prophylactic itraconazole. If strategies for the prevention of disseminated histoplasmosis in HIV-infected patients are to be improved, studies must better define the risk factors for this opportunistic infection, describe its natural history, and develop more reliable tests to predict its development.

Vaccination with recombinant heat shock protein 60 from Histoplasma capsulatum protects mice against pulmonary histoplasmosis

HIS-62 is a glycoprotein that has been isolated from the cell wall and cell membrane fraction of the pathogenic fungus Histoplasma capsulatum. It is a target of the cellular immune response to this fungus, and it protects mice against a lethal intravenous inoculum of H. capsulatum yeast cells. In this study, we cloned the gene encoding this antigen to reveal its biological nature and studied the immunological activity of recombinant antigen. The amino acid sequences of the NH2 terminus and internal peptides were obtained by Edman degradation. Degenerate oligonucleotides were used to isolate a gene fragment of HIS-62 by PCR. One 680-bp segment that corresponded to the known peptide sequence was amplified from H. capsulatum DNA. This DNA was used to screen a genomic library, and the full-length gene was isolated and sequenced. The deduced amino acid sequence of the gene demonstrated approximately 70 and approximately 50% identity to heat shock protein 60 (hsp 60) from Saccharomyces cerevisiae and hsp 60 from Escherichia coli, respectively. A cDNA was synthesized by reverse transcription PCR and was expressed in E. coli. Recombinant protein reacted with a monospecific polyclonal rabbit antiserum raised against native HIS-62, with monoclonal HIS-62-reactive T cells, and with splenocytes from mice immunized with viable yeast cells. Moreover, vaccination with the recombinant protein conferred protection in mice against a lethal intranasal inoculation with yeast cells. Thus, HIS-62 is a member of the hsp 60 family, and the recombinant hsp 60 is protective against pulmonary histoplasmosis in mice.

Prevention of relapse of histoplasmosis with fluconazole in patients with the acquired immunodeficiency syndrome

OBJECTIVE

To assess the effectiveness of fluconazole for suppression of relapse of histoplasmosis in patients with acquired immunodeficiency syndrome (AIDS).

DESIGN

Retrospective, nonrandomized, open trial.

SETTING

Multicenter at two university referral centers and in five private practices.

PATIENTS

Seventy-six patients with AIDS and disseminated histoplasmosis who completed induction treatment with amphotericin B, itraconazole, or fluconazole and maintained on treatment with fluconazole to prevent relapse.

INTERVENTIONS

Fluconazole was given at dosages of 100 to 400 mg per day. Patients were followed by their primary physicians, who completed questionnaires collecting information about treatment and relapse status. Blood and urine specimens were submitted periodically for Histoplasma capsulatum var. capsulatum antigen determination.

MEASUREMENTS AND MAIN RESULTS

Nine of the 76 patients relapsed during fluconazole therapy and another was removed from the study because of allergic rash. Survival after initiation of therapy for histoplasmosis was 94 weeks, ranging from 74 weeks for those who received less than 1 g of amphotericin B for induction and none for maintenance therapy to 156 weeks for those who received greater than 1 g for induction and additional amphotericin B for maintenance therapy before beginning fluconazole (P < 0.02). Antigen levels fell at rates of 0.05 units/week in urine and 0.02 units/week in serum in patients who were successfully maintained in remission and increased by > or = 2 units/week in 4 of 6 patients who relapsed.

CONCLUSIONS

Fluconazole > or = 200 mg daily is a reasonable choice for chronic suppressive therapy of histoplasmosis in patients who cannot take itraconazole because of drug interactions, malabsorption, or side effects.

Mycotic morbidity--an occupational risk for mycologists

Classical mycologists may be at a greater risk for infection with organisms under investigation than medical mycologists. The methods of infection of human beings by systemic mycotic pathogens is known. These principles can be used to develop good laboratory practices for classical mycological investigators. Newly recognized fungal pathogens and a more susceptible population may cause more laboratory infections. Minimal safety practices to prevent mycotic morbidity are described.

Protective effect of poly-2-vinylpyridine-N-oxide on susceptibility of silica-treated mice to experimental histoplasmosis

We have studied the ability of poly-2-vinylpyridine-N-oxide (PVNO), a lysosomal stabilizing agent, to abrogate the cytotoxic effects of silica on macrophages. Male C3H/HeN mice were pretreated with PVNO and inoculated intravenously with silica particles. At 24 h after silica injection, silica-treated and -untreated mice were challenged intravenously with varying doses of live yeast cells of Histoplasma capsulatum. All mice receiving silica died when challenged with 5 X 10(5) yeast cells of Histoplasma sp. compared with no deaths in PVNO-pretreated animals and 10% mortality in controls not receiving PVNO or silica. When animals were given 2.5 X 10(5) yeast cells (a sublethal dose), the protective effect of PVNO was seen by a reduction in splenomegaly and viable Histoplasma sp. present in the spleen. Furthermore, PVNO alone showed a significant protective effect (P less than 0.05) against a lethal challenge with Histoplasma sp. Prior treatment with PVNO also protected mouse peritoneal macrophages from the cytotoxic effects of silica particles in vitro. These results indicate that PVNO abrogates the cytotoxicity of silica particles on macrophages and also increases the resistance of mice to histoplasmosis.

Decontamination of a Histoplasma capsulatum-infested bird roost in Illinois

Histoplasma capsulatum was isolated from 27 of 34 soil specimens collected from a 3.23-hectare (8-acr) estate in illinois that had been the site of a bird roost for more than 10 yr. When the estate was sold to a developer for for the construction of a shopping center, it was feared that disturbing the roost would cause airborne transmission of spores of H. Capsulatum and thus create a public health hazard for the workmen and surrounding community. To prevent this, the bird roost was decontaminated with the application of 3,785 ml (1 gallon) of 3% formalin per square foot of soil. Safety precautions were taken to minimize the inhalation of dust and formalin by the decontamination team. Thirty-five soil specimens collected after application of the formalin were negative for H. capsulatum. No cases of histoplasmosis occurred among the decontamination workers, construction crews, or the general population. The total cost of the decontamination project was $75,000.

Suppression of cryptococcosis and histoplasmosis by ketoconazole in athymic nude mice

Congenitally athymic nude (nu/nu) mice are more susceptible to disseminated cryptococcosis and histoplasmosis than their heterozygous (nu/ + ) thymus-bearing litter-mates. The therapeutic efficacy of ketoconazole, an orally absorbable antifungal agent, was evaluated in nu/nu and nu/ + mice infected intraperitoneally with Cryptococcus neoformans and Histoplasma capsulatum. Two- to five-week courses of ketoconazole significantly prolonged the survival of nu/nu mice infected with either fungus in dose-dependent fashion, but death eventually followed discontinuance of therapy. More significant protection was seen in nu/ + mice infected with C. neoformans, and markedly lower fungal counts in organs, with some negative cultures, were seen in ketoconazole-treated nu/ + mice infected with H. capsulatum. These studies indicate that ketoconazole is effective against both fungi, although results of treatment are much better in the immunologically intact nu/ + host.