Digestion of Histoplasma capsulatum yeasts by human macrophages

The strategies used by Histoplasma capsulatum yeasts to survive and multiply within human macrophages (M phi) are unknown. To better understand these strategies we studied the intracellular fate of viable vs heat-killed (HK) yeasts in human monocyte-derived M phi. Initial studies demonstrated that phagolysosome fusion was present in M phi ingesting either viable or HK yeasts. Viable yeasts multiplied within M phi phagolysosomes, whereas M phi completely digested intracellular FITC-labeled HK yeasts within 24 h after ingestion. This observation was confirmed by electron microscopy. M phi that had ingested colloidal gold-labeled HK yeasts contained gold particles but no visible yeasts at 24 h. Digestion of HK yeasts was evident as early as 4 h after phagocytosis, and was complete by 24 h. M phi digestion of HK yeasts was blocked completely when M phi were cultured for 24 h in the presence of chloroquine. In M phi simultaneously ingesting both viable and HK yeasts, viable yeasts multiplied, but HK yeasts were digested within the same cell. M phi that had ingested viable yeasts digested them completely when M phi were cultured for 24 h in the presence of cycloheximide or amphotericin B. Coculture of infected M phi with nystatin or ketoconazole resulted in inhibition of growth, but the yeasts were not digested. These data indicate that: 1), HK Hc yeasts are easily digested by preformed M phi lysosomal hydrolases; 2), viable Hc yeasts survive and multiply within M phi phagolysosomes, but the yeasts do not secrete a factor(s) that affects the ability of other phagolysosomes within the same M phi to digest killed yeasts; and 3), inhibition of yeast protein synthesis or cell wall biosynthesis is sufficient to render viable yeasts susceptible to digestion by human M phi.

Digestion of Histoplasma capsulatum yeasts by human macrophages

The strategies used by Histoplasma capsulatum yeasts to survive and multiply within human macrophages (M phi) are unknown. To better understand these strategies we studied the intracellular fate of viable vs heat-killed (HK) yeasts in human monocyte-derived M phi. Initial studies demonstrated that phagolysosome fusion was present in M phi ingesting either viable or HK yeasts. Viable yeasts multiplied within M phi phagolysosomes, whereas M phi completely digested intracellular FITC-labeled HK yeasts within 24 h after ingestion. This observation was confirmed by electron microscopy. M phi that had ingested colloidal gold-labeled HK yeasts contained gold particles but no visible yeasts at 24 h. Digestion of HK yeasts was evident as early as 4 h after phagocytosis, and was complete by 24 h. M phi digestion of HK yeasts was blocked completely when M phi were cultured for 24 h in the presence of chloroquine. In M phi simultaneously ingesting both viable and HK yeasts, viable yeasts multiplied, but HK yeasts were digested within the same cell. M phi that had ingested viable yeasts digested them completely when M phi were cultured for 24 h in the presence of cycloheximide or amphotericin B. Coculture of infected M phi with nystatin or ketoconazole resulted in inhibition of growth, but the yeasts were not digested. These data indicate that: 1), HK Hc yeasts are easily digested by preformed M phi lysosomal hydrolases; 2), viable Hc yeasts survive and multiply within M phi phagolysosomes, but the yeasts do not secrete a factor(s) that affects the ability of other phagolysosomes within the same M phi to digest killed yeasts; and 3), inhibition of yeast protein synthesis or cell wall biosynthesis is sufficient to render viable yeasts susceptible to digestion by human M phi.

Inhibition of intracellular growth of Histoplasma capsulatum yeast cells by cytokine-activated human monocytes and macrophages

Human monocytes/macrophages (M psi) were infected with Histoplasma capsulatum yeast cells, and intracellular growth was quantified after 24 h of incubation in medium alone or in medium containing cytokines. Yeast cells multiplied within freshly isolated monocytes, cultured M psi, and alveolar M psi with intracellular generation times of 14.2 +/- 1.4, 18.5 +/- 2.1, and 19.9 +/- 1.9 h (mean +/- standard error of the mean), respectively. Monocytes and M psi inhibited the intracellular growth of yeast cells in response to cytokine supernatant; maximum inhibition was obtained when cytokines were added to cell monolayers immediately after infection. Opsonization of yeast cells in normal serum or in H. capsulatum-immune serum did not affect the intracellular generation time of yeast cells in either control M psi or cytokine-activated M psi.

Immunological aspects of fungal pathogenesis

The incidence of infection with the pathogenic fungi continues to escalate, especially in the era of the acquired immune deficiency syndrome. To the clinician, this heterogeneous group of organisms poses both a diagnostic and a therapeutic challenge. Consequently, growing numbers of investigators are seeking to elucidate the pathogenetic mechanisms involved in disease caused by medically important fungi. In this review, many of the recent scientific advances that have been made in the immunological aspects of the pathogenesis of fungal infections are presented. The topics covered include 1) the receptors for fungi on the surface of professional phagocytes; 2) the mechanisms for killing and growth inhibition of fungi by phagocytes; 3) the means by which fungi evade host defenses; 4) the role of humoral immunity in fungal infection; 5) immunoregulation in fungal infections; and 6) the influence of cytokines on host defenses against pathogenic fungi.

Phagocytosis of Histoplasma capsulatum yeasts and microconidia by human cultured macrophages and alveolar macrophages. Cellular cytoskeleton requirement for attachment and ingestion

Phagocytosis of Histoplasma capsulatum (Hc) yeasts and microconidia by human macrophages (M phi) was quantified by a fluorescence quenching technique. Phagocytosis of unopsonized Hc yeasts by monocyte-derived M phi and human alveolar M phi (AM) was rapid. After 60 min, 79% of cultured M phi and 59% of AM had ingested an average of 9.8 and 11 yeasts/M phi, respectively. In contrast, only 26% of monocytes ingested 4.5 yeasts/cell after 60 min. Phagocytosis of unopsonized microconidia by cultured M phi and by AM was equivalent. Monoclonal antibodies specific for the alpha-chains and beta-chain of the CD18 family of adhesion receptors inhibited the binding of Hc yeasts and microconidia to cultured M phi and AM. Thus, the M phi CD18 complex mediates recognition of both phases of this dimorphic fungus. Disruption of actin microfilaments with cytochalasin D inhibited both attachment and ingestion of yeasts by M phi. In contrast, nocodazole, which prevents polymerization of microtubules, did not inhibit binding or ingestion. Both drugs inhibited ingestion, but neither drug inhibited binding of C3b- and C3bi-coated sheep erythrocytes to complement receptors type one (CR1) or type three (CR3), respectively. Therefore, different signal transducing mechanisms for phagocytosis appear to be triggered by the binding of Hc yeasts to CD18, and by the binding of EC3bi to CD11b/CD18, respectively.

Correlative studies of blastogenic responses and interleukin 1 production by mononuclear cells from patients with zoopathogenic fungal infections

The production of interleukin 1 (IL 1) by adherent peripheral blood mononuclear cells (PBMC) was quantitated in 16 individuals infected with Histoplasma capsulatum or Blastomyces dermatitidis and 16 age-matched controls. In parallel, we measured blastogenic responses to phytohemagglutinin (PHA) by PBMC from patients and controls. Of the 16 patients, six had pulmonary histoplasmosis, six had disseminated histoplasmosis, two had pulmonary blastomycosis, and two had disseminated blastomycosis. At the time of study, none of the patients were receiving immunosuppressive agents or had an underlying debilitating illness. Proliferative responses by PBMC from patients to PHA were significantly (P less than 0.05) less than the mean response by PBMC from an equal number of controls. In the 16 controls, the increase in secretion of IL 1 by lipopolysaccharide (LPS)-stimulated adherent cells over unstimulated cells ranged from 18 to 40 units of IL 1 activity per 10(5) adherent cells. The increment in IL 1 levels between LPS-stimulated adherent PBMC and unstimulated cells was diminished (less than 18 units of IL 1 activity per 10(5) adherent cells) in five of the 16 patients. Diminished IL 1 secretion in response to LPS was associated with impaired PHA responses in four of 10 patients.

Clinical evaluation of efficacy, pharmacokinetics, and safety of teicoplanin for serious gram-positive infections

Nineteen patients hospitalized for serious gram-positive infections were treated with teicoplanin, a new glycopeptide antibiotic. A variety of infections were treated, including endocarditis, septic thrombophlebitis, osteomyelitis, pyogenic arthritis, and soft tissue infection. Of 13 infections that could be evaluated in 12 patients, there were 8 clinical cures, 2 improvements, 1 recurrence, and 2 failures. Of the eight patients with Staphylococcus aureus bacteremia, seven were clinically cured or improved with teicoplanin therapy. Of the nine patients in whom the bacteriological response to treatment could be fully evaluated, six were cured; there was recurrence of infection in one, and treatment failed in two patients. In vitro testing showed the 13 bacterial isolates (9 S. aureus, 3 S. epidermidis, and 1 group B streptococcus) to be uniformly susceptible to teicoplanin, with MICs ranging from 0.12 to 0.5 microgram/ml. Every isolate was more susceptible in vitro to teicoplanin than to vancomycin. Three of the staphylococcal isolates were resistant to methicillin. Pharmacokinetic studies demonstrated that after an initial drug-accumulation period, a single daily dose adequately maintained the teicoplanin concentrations in serum within therapeutic ranges. Teicoplanin also penetrated well into synovial fluid. The drug was well tolerated by either intravenous or intramuscular administration. The most significant adverse reaction was an urticarial rash which required discontinuation of therapy in one patient; a second patient experienced a modest decrease in high-frequency auditory threshold. Asymptomatic eosinophilia and mild elevation of serum transaminases were noted as well. The results of this study suggest that teicoplanin is a safe and effective new agent for treatment of serious infections caused by gram-positive organisms.

Role of the adherence-promoting receptors, CR3, LFA-1, and p150,95, in binding of Histoplasma capsulatum by human macrophages

The principal host cell of H. capsulatum (Hc) is the M phi within which the pathogenic yeast phase of the fungus multiplies during active disease. The initial interaction between Hc yeasts and M phi therefore is a crucial step in the pathogenesis of histoplasmosis. In the present study, we have identified the major receptor mechanism that mediates the attachment of unopsonized Hc yeasts to human monocyte-derived M phi from peripheral blood. Binding of Hc yeasts by M phi is rapid, temperature dependent, and requires both Ca and Mg ions for optimum activity. Recognition of Hc yeasts does not require Fc receptors, mannosyl/fucosyl receptors, beta-glucan receptors, or secretion of C3 by M phi. Studies were performed on the effect of down regulating specific receptors of the CR3/LFA-1/p150,95 adherence-promoting protein family from the apical portion of M phi to determine the effects upon binding of Hc yeasts. Anti-beta chain mAbs that recognize all three of these proteins blocked binding of yeasts. However, removal of individual receptors with antibodies against the alpha polypeptides caused negligible depression of binding, and removal of any pair caused only modest depression. Thus, each of the members of the CR3/LFA-1/p150,95 family is independently capable of binding Hc. The delineation of this new mechanism for nonopsonic recognition by M phi that is exploited by Hc yeasts will aid in future studies to identify the Hc ligand, to elucidate the stoichiometry of CR3/LFA-1/p150,95 binding, and to determine triggering mechanisms for release of toxic oxygen metabolites.

Development and characterization of Histoplasma capsulatum-reactive murine T-cell lines and clones

Experimental studies have suggested that antigen-specific T lymphocytes are important mediators of resistance to infection with the pathogenic fungus Histoplasma capsulation. To gain a better understanding of the role of T lymphocytes, we developed murine T-cell lines and clones that recognized Histoplasma antigens. These T cells were of the helper/inducer phenotype (Thy-1.2+ Lyt-1+ L3T4+ Lyt-2-) and exerted multiple immunological functions. T-cell lines and 12 clones proliferated vigorously in response to histoplasmin; the T-cell lines and 6 clones also were reactive with heterologous fungal antigens prepared from either Blastomyces dermatitidis or Coccidioides immitis. Recognition of antigen by T cells was H-2 restricted; in the absence of antigen, four clones demonstrated alloreactivity. All T-cell clones conferred local delayed-type hypersensitivity responses when injected with antigen into footpads of mice. Ten of 12 T-cell clones released interleukin-2 after stimulation with antigen, and all clones tested secreted interferon. Moreover, culture supernatants from antigen-stimulated clones armed peritoneal macrophages to inhibit intracellular growth of H. capsulatum yeast cells. All clones assayed exerted nonspecific help. Thus, development of T-cell clones should facilitate analysis of the regulatory properties of Histoplasma-specific T cells.

The pathogenesis of experimental pulmonary histoplasmosis. Correlative studies of histopathology, bronchoalveolar lavage, and respiratory function

A murine model of acute pulmonary histoplasmosis was employed to study the pathogenesis of the disease process by means of histopathology, bronchoalveolar lavage, and respiratory function tests. These studies were performed on C57BL/6 mice from 8 h to 8 wk after intranasal inoculation of 10(5) yeast forms of Histoplasma capsulatum and on age-matched control animals that received saline only. At Week 1, the histopathology was characterized by subacute inflammation consisting of polymorphonuclear leukocytes (PMN), lymphocytes, and macrophages that infiltrated the interstitium around small bronchioles and adjacent alveoli. At Weeks 2 and 4, the infiltrates were comprised predominantly of lymphocytes and macrophages; noncaseating granulomas were present at Week 2. Aggregates of lymphoid cells were prominent along the bronchial tree and in perivascular distribution. Those in close contact with bronchiolar epithelium resembled hyperplastic bronchus associated lymphoid tissue. Quantitative studies of cells in the BAL fluid revealed a large influx of PMN at Week 1 with return to normal range by Week 2. At this time there was a significant (p less than 0.02) increase in lymphocytes that persisted through Week 8, although histopathologic changes were minimal in lung at this time. A significant decrease in the DLCO/TLC at Week 2 in association with a normal vital capacity indicated impairment of respiratory function secondary to the alveolitis induced by H. capsulatum infection rather than a reduction of lung volume. This model offers promise for additional correlative studies of lymphocyte subsets in lung tissue and alveolar spaces as well as of the functions subserved by these respective populations.

Modulation of cellular immune responses in mice with disseminated histoplasmosis by recombinant interleukin-2

Depression of the cellular immune responses in mice with disseminated histoplasmosis is associated with deficient production of interleukin-2 (IL-2) by splenocytes. Therefore, we examined whether a highly purified preparation of IL-2, recombinant human IL-2 (rIL-2), could modify the cellular immune responses in infected mice and whether this lymphokine could alter the severity of histoplasmosis in animals. Exogenous rIL-2, at concentrations of up to 1,000 U/ml, failed to augment the proliferative responses to concanavalin A by unfractionated splenocytes or splenic T cells from mice infected for 1 week. In addition, rIL-2 did not modulate the plaque-forming cell response to sheep erythrocytes by splenocytes from these same mice. However, at week 3, rIL-2 in concentrations ranging from 10 to 1,000 U/ml considerably augmented the proliferative response to concanavalin A and plaque-forming cell response to sheep erythrocytes by splenocytes from infected mice. Kinetics studies demonstrated that rIL-2 exerted maximal immunoregulatory activity when added on day 0 or 1 to cultures of splenocytes. In vivo administration of rIL-2, 200 to 20,000 U/day, for 10 days to normal and 3-week-infected mice did not alter the proliferative activity of splenocytes to concanavalin A; 200,000 U of rIL-2 per day actually depressed the proliferative responses of splenocytes from normal and infected mice. In vivo, rIL-2 did not modify delayed-type hypersensitivity responses to sheep erythrocytes or to histoplasmin by normal and infected mice. Moreover, treatment with rIL-2 in vivo did not reduce the number of Histoplasma CFU in spleens of mice. Thus, despite the immunoenhancing effect of rIL-2 in vitro, this lymphokine failed to exert similar effects in vivo.

A study of the immunological effects of cimetidine in patients with lepromatous leprosy

To test the capacity of cimetidine to enhance cellular immunity in patients with lepromatous leprosy (LL), cimetidine was given for one month to 29 inactive LL patients and 3 active LL patients. Immune function was monitored with skin tests (lepromin, PPD, candida, and trichopytin), lymphocyte transformation tests (phytohemagglutinin, BCG, and Dharmendra lepromin), and quantitation of peripheral blood lymphocyte subpopulations. A small but significant "booster" response to PPD was the only change observed in the study of patients with inactive disease, and leprosy-related reactions did not occur. In the few active LL patients studied, neither immune enhancement nor leprosy-related reactions were observed. The results of this investigation suggest that cimetidine can be used safely in patients with inactive lepromatous leprosy.

Immunoregulation in disseminated murine histoplasmosis: disturbances in the production of interleukins 1 and 2

Production of IL 1 and IL 2 by splenocytes from C57BL/6 mice was measured at wk 1, 3, 8, and 14 after i.v. inoculation with 6 X 10(5) Histoplasma capsulatum (Hc) yeasts. As compared with age-matched controls, IL 1 production by splenocytes from Hc-infected mice was reduced severely at wk 1 and 3 of infection, greater than normal at wk 8, and within normal range at wk 14. IL 2 production was also reduced at wk 1 and 3 of infection; it was normal at wk 8 and was elevated at wk 14. Indomethacin and catalase failed to restore IL 1 production by splenocytes from infected mice, and exogenous IL 1 did not augment IL 2 production by these cells. A factor capable of suppressing the activity of IL 2 was detected in supernatants of concanavalin A-stimulated splenocytes from infected animals at wk 1 and 3 of infection, respectively. No factor capable of suppressing IL 1 activity was detected. Thus, the deficits of cell-mediated immunity in mice with systemic Hc infection may derive, in part, from impaired amplification of the immune response consequent to abnormal generation of IL 1 and IL 2.

Immunoregulation in disseminated murine histoplasmosis: disturbances in the production of interleukins 1 and 2

Production of IL 1 and IL 2 by splenocytes from C57BL/6 mice was measured at wk 1, 3, 8, and 14 after i.v. inoculation with 6 X 10(5) Histoplasma capsulatum (Hc) yeasts. As compared with age-matched controls, IL 1 production by splenocytes from Hc-infected mice was reduced severely at wk 1 and 3 of infection, greater than normal at wk 8, and within normal range at wk 14. IL 2 production was also reduced at wk 1 and 3 of infection; it was normal at wk 8 and was elevated at wk 14. Indomethacin and catalase failed to restore IL 1 production by splenocytes from infected mice, and exogenous IL 1 did not augment IL 2 production by these cells. A factor capable of suppressing the activity of IL 2 was detected in supernatants of concanavalin A-stimulated splenocytes from infected animals at wk 1 and 3 of infection, respectively. No factor capable of suppressing IL 1 activity was detected. Thus, the deficits of cell-mediated immunity in mice with systemic Hc infection may derive, in part, from impaired amplification of the immune response consequent to abnormal generation of IL 1 and IL 2.

Evolution of inflammatory response and cellular immune responses in a murine model of disseminated blastomycosis

A reproducible model of disseminated blastomycosis was established in C57BL/6 mice by intravenous injection of 10(6) yeast-phase Blastomyces dermatiditis organisms. The infection progressed over 5 weeks to involve lungs, brains, superficial fascia, livers, and spleens of mice. By week 5, there was a greater number of organisms in lungs and brains than in livers and spleens. The tissue response in lungs, brains, and livers progressed from acute neutrophilic invasion before week 1 to pyogranuloma formation by week 5. Lymph nodes and spleens were remarkably spared. By week 5, infected mice became anergic to intradermal challenge with both specific Blastomyces antigen and a nonspecific antigen (sheep erythrocytes). At this time, the response to concanavalin A or phytohemagglutinin by splenocytes was markedly less than that of normal controls. Likewise, the plaque-forming cell response to sheep erythrocytes by splenocytes from infected mice was diminished. In coculture studies, splenocytes from 5-week-infected mice reduced the plaque-forming cell response by normal splenocytes. The development of this murine model should prove useful for elucidating the perturbations of immunoregulation associated with disseminated blastomycosis.

Clinical trial of the efficacy and safety of ticarcillin and clavulanic acid

Forty-three hospitalized patients were treated with a new antibiotic combination containing ticarcillin plus the beta-lactamase inhibitor, clavulanic acid, in a fixed combination for intravenous use. A variety of infections were treated, including pneumonia, bacteremia, urinary tract infection, and osteomyelitis. Of 50 episodes of infection in 43 patients, 44 clinical cures were obtained, with 5 patients improving and 1 patient failing to respond to treatment. In vitro susceptibility testing of 101 clinical isolates was notable for the rarity of resistance to the combination antibiotic. Of specific interest, all 14 isolates of Staphylococcus aureus were susceptible to ticarcillin plus clavulanic acid, whereas only 2 of the 14 isolates were susceptible to ticarcillin alone. Adverse reactions to the study drug were minimal; eosinophilia, unaccompanied by other allergic phenomena, and oral candidiasis were most frequent. Overall, the combination of ticarcillin with the beta-lactamase inhibitor, clavulanic acid, appears to be a safe and effective drug for the treatment of infections caused by susceptible organisms.

Bronchoalveolar lavage in acute drug-hypersensitivity pneumonitis probably caused by phenytoin

We have reported a case of acute hypersensitivity pneumonitis, probably caused by phenytoin, in which the results of bronchoalveolar lavage suggested a predominantly lymphocytic type of alveolitis, comparable to the alveolitis of sarcoidosis or chronic hypersensitivity pneumonitis.

Flow microfluorometry analysis of alterations in T-lymphocyte subsets during murine listeriosis

C57BL/6 mice were infected intravenously with 6 X 10(3) Listeria monocytogenes organisms. As early as day 3 of infection, there was a marked reduction in the number of lymphocytes recovered from the peripheral blood, bone marrow, and thymuses of infected animals. Concomitantly, there was an increase in the number of splenic lymphocytes. By day 14, both the total and differential cell counts were similar in both infected and normal animals. Flow microfluorometric studies comparing the Thy-1.2, Lyt-1, Lyt-2, and surface immunoglobulin (SIg) phenotypes of lymphocytes from normal and infected mice were performed. Between days 3 and 5, there was a decrease in the percentage of Thy-1.2+ cells in the spleens of L. monocytogenes-infected animals. Conversely, the percentages of Lyt-1+, Lyt-2+, and SIg+ cells remained constant. At day 7 of infection, the percentage of Thy-1.2+ splenocytes was within normal limits, and at day 10, the percentage of Thy-1.2+ cells was elevated slightly. The absolute numbers of Thy-1.2+ cells were comparable in both infected and normal animals at early stages (days 3 to 5) of L. monocytogenes infection, but there was a marked elevation of Thy-1.2+ splenocytes at days 7 to 14 of infection. Lyt-1+, Lyt-2+, and SIg+ splenocytes increased in absolute numbers as early as day 3 of infection and were still elevated at day 14. Adrenalectomy before infection had no effect on the results obtained, suggesting that these changes were not mediated by endogenous steroids.

Cellular origins and target cells of immunoregulatory factors in mice with disseminated histoplasmosis

Disseminated infection with Histoplasma capsulatum stimulates the production of a suppressor factor (SF-H) by spleen cells from C3H/HeJ mice and a helper factor (HF-H) by spleen cells from C57BL/6 mice. In the present study these disparate immunoregulatory factors were analyzed in detail with regard to: a) the surface phenotype of the cells that produce SF-H and HF-H; b) the role of accessory cells in the production of these factors; and c) the surface phenotype of the target cells activated by SF-H and HF-H. Treatment of spleen cells from Histoplasma-infected C3H/HeJ mice with anti-Thy-1.2 plus complement (C) or with anti-Ly-2 plus C or with anti-I-Jk antiserum plus C abolished production of SF-H. Conversely, generation of HF-H by spleen cells from C57BL/6 mice was abrogated by treatment with either anti-Thy-1.2 plus C or with anti-Ly-1 plus C. Thus, a Thy-1.2+, Ly-2+, I-J+ T cell releases SF-H, and a Thy-1.2+, Ly-1+ T cell secretes HF-H. Production of SF-H and HF-H by splenic T cells was reduced markedly by depletion of macrophages (M phi); readdition of 1% syngeneic, plastic-adherent splenocytes from normal or infected mice to M phi-depleted, splenic T cell cultures of either strain restored the capacity to generate immunoregulatory factors. Furthermore, adherent splenocytes from normal or infected mice liberated a factor or factors that enhanced production of both SF-H and HF-H. Kinetic studies demonstrated that activation of normal spleen cells required at least 48 hr of exposure to SF-H or HF-H. Both factors failed to activate splenocytes pretreated with anti-Thy-1.2 plus C. Spleen cells from C3H/HeJ mice depleted of Ly-1+, Ly-2+, or I-J+ cells and exposed to SF-H did not demonstrate suppressor activity, whereas Ly-1-depleted splenocytes from C57BL/6 mice exposed to HF-H failed to exert helper activity. Therefore, the target of SF-H is a Thy-1.2+, Ly-1+2+, I-J+ T cell, and the target of HF-H is a Thy-1.2+, Ly-1+ T cell.

Cellular origins and target cells of immunoregulatory factors in mice with disseminated histoplasmosis

Disseminated infection with Histoplasma capsulatum stimulates the production of a suppressor factor (SF-H) by spleen cells from C3H/HeJ mice and a helper factor (HF-H) by spleen cells from C57BL/6 mice. In the present study these disparate immunoregulatory factors were analyzed in detail with regard to: a) the surface phenotype of the cells that produce SF-H and HF-H; b) the role of accessory cells in the production of these factors; and c) the surface phenotype of the target cells activated by SF-H and HF-H. Treatment of spleen cells from Histoplasma-infected C3H/HeJ mice with anti-Thy-1.2 plus complement (C) or with anti-Ly-2 plus C or with anti-I-Jk antiserum plus C abolished production of SF-H. Conversely, generation of HF-H by spleen cells from C57BL/6 mice was abrogated by treatment with either anti-Thy-1.2 plus C or with anti-Ly-1 plus C. Thus, a Thy-1.2+, Ly-2+, I-J+ T cell releases SF-H, and a Thy-1.2+, Ly-1+ T cell secretes HF-H. Production of SF-H and HF-H by splenic T cells was reduced markedly by depletion of macrophages (M phi); readdition of 1% syngeneic, plastic-adherent splenocytes from normal or infected mice to M phi-depleted, splenic T cell cultures of either strain restored the capacity to generate immunoregulatory factors. Furthermore, adherent splenocytes from normal or infected mice liberated a factor or factors that enhanced production of both SF-H and HF-H. Kinetic studies demonstrated that activation of normal spleen cells required at least 48 hr of exposure to SF-H or HF-H. Both factors failed to activate splenocytes pretreated with anti-Thy-1.2 plus C. Spleen cells from C3H/HeJ mice depleted of Ly-1+, Ly-2+, or I-J+ cells and exposed to SF-H did not demonstrate suppressor activity, whereas Ly-1-depleted splenocytes from C57BL/6 mice exposed to HF-H failed to exert helper activity. Therefore, the target of SF-H is a Thy-1.2+, Ly-1+2+, I-J+ T cell, and the target of HF-H is a Thy-1.2+, Ly-1+ T cell.

Immunoregulation in experimental disseminated histoplasmosis: flow microfluorometry (FMF) studies of the Thy and Lyt phenotypes of T lymphocytes from infected mice

Previous studies have shown that mice infected i.v. with 6 X 10(5) yeast phase Histoplasma capsulatum (Hc) develop suppressed immune responses during weeks 1 to 4 of infection but that by weeks 8 to 12 of infection these responses return to normal. In this study total and differential cell counts showed that as early as the third day of infection there was a marked reduction in the number of lymphocytes recovered from the peripheral blood, bone marrow, and thymus of infected animals. Concomitantly, there was an increase in the number of splenic lymphocytes. By day 28 both the total and differential cell counts were similar in both infected and normal animals. Flow microfluorometric (FMF) studies comparing the Thy-1.2, Lyt-1, Lyt-2, and surface immunoglobulin (slg) phenotypes of lymphocytes from normal and infected mice were performed. Between days 5 and 7 the thymocytes from infected mice displayed a higher relative fluorescence intensity (RFI) of the Thy-1.2 marker than normal thymocytes, whereas at day 10, the RFI was less than that of normal thymic lymphocytes. Between days 7 and 10 of infection the RFI of the Lyt-2 marker was less on thymocytes from Hc-infected mice; however, there was no change in the Lyt-1 marker. Examination of these lymphocyte markers in blood, spleen, and mesenteric lymph nodes showed that there were decreases in the RFI of both the Thy-1.2 and Lyt-2 between days 5 and 10 of infection. No changes were observed in the Lyt-1 or slg markers. By day 28 there were no differences between the normal and infected mice with respect to any surface marker in any of the organs studied. In other experiments, the effect of adrenalectomy before infection on these surface markers was studied. Absolute numbers of Thy-1.2+, Lyt-1+, and Lyt-2+ cells were significantly increased in the spleen and significantly decreased in the thymus and peripheral blood of infected mice relative to normal controls. These studies suggest that there is a migration of cells from the thymus, blood, and bone marrow to the spleens of mice with disseminated Hc infection.

Immunoregulation in experimental disseminated histoplasmosis: flow microfluorometry (FMF) studies of the Thy and Lyt phenotypes of T lymphocytes from infected mice

Previous studies have shown that mice infected i.v. with 6 X 10(5) yeast phase Histoplasma capsulatum (Hc) develop suppressed immune responses during weeks 1 to 4 of infection but that by weeks 8 to 12 of infection these responses return to normal. In this study total and differential cell counts showed that as early as the third day of infection there was a marked reduction in the number of lymphocytes recovered from the peripheral blood, bone marrow, and thymus of infected animals. Concomitantly, there was an increase in the number of splenic lymphocytes. By day 28 both the total and differential cell counts were similar in both infected and normal animals. Flow microfluorometric (FMF) studies comparing the Thy-1.2, Lyt-1, Lyt-2, and surface immunoglobulin (slg) phenotypes of lymphocytes from normal and infected mice were performed. Between days 5 and 7 the thymocytes from infected mice displayed a higher relative fluorescence intensity (RFI) of the Thy-1.2 marker than normal thymocytes, whereas at day 10, the RFI was less than that of normal thymic lymphocytes. Between days 7 and 10 of infection the RFI of the Lyt-2 marker was less on thymocytes from Hc-infected mice; however, there was no change in the Lyt-1 marker. Examination of these lymphocyte markers in blood, spleen, and mesenteric lymph nodes showed that there were decreases in the RFI of both the Thy-1.2 and Lyt-2 between days 5 and 10 of infection. No changes were observed in the Lyt-1 or slg markers. By day 28 there were no differences between the normal and infected mice with respect to any surface marker in any of the organs studied. In other experiments, the effect of adrenalectomy before infection on these surface markers was studied. Absolute numbers of Thy-1.2+, Lyt-1+, and Lyt-2+ cells were significantly increased in the spleen and significantly decreased in the thymus and peripheral blood of infected mice relative to normal controls. These studies suggest that there is a migration of cells from the thymus, blood, and bone marrow to the spleens of mice with disseminated Hc infection.

Rifampin in the treatment of leprosy

The minimal inhibitory concentration of rifampin for Mycobacterium leprae is less than 1 microgram/ml. Therapy with rifampin has proved efficacious both in mice experimentally infected with M. leprae and in humans with leprosy. Rifampin kills M. leprae more rapidly than do other antileprosy drugs currently available. Consequently, M. leprae bacilli from patients with lepromatous disease are rendered noninfectious within three weeks after the institution of rifampin therapy, as determined in the mouse footpad test system. Administration of this antibiotic substantially reduces the quantities of M. leprae discharged in the nasal secretions of lepromatous patients within three weeks, thus rapidly decreasing the potential infectivity of these individuals. Intermittent rifampin therapy for leprosy has been successful, with a low incidence of adverse reactions to the drug. Worldwide, the prevalence of primary and secondary resistance of M. leprae to dapsone has increased markedly. Therefore, the World Health Organization recommends a multidrug regimen that includes intermittent administration of rifampin for the treatment of leprosy.

Pharmacological modulation of suppressor cell activity in mice with disseminated histoplasmosis

Indomethacin and cyclophosphamide (CY) were used in an attempt to modify the suppressive effects of spleen cell populations from mice with disseminated histoplasmosis at 1 week of infection. In vitro addition of indomethacin did not alter the depressed plaque-forming cell response to sheep erythrocytes of normal spleen cells cocultured with unfractionated or nylon wool-fractionated spleen cells from infected mice. Likewise, indomethacin given intraperitoneally did not enhance the subnormal in vivo plaque-forming cell response of spleen cells from infected mice. Conversely, 20 mg of CY per kg given intraperitoneally 2 days before or 6 h after the inoculation with Histoplasma capsulatum partially reversed the suppression effected by splenic T cells (nylon wool passed) in vitro, whereas 50 mg of CY per kg given intraperitoneally 6 h after the injection of H. capsulatum ablated suppressor T cell activity in vitro; neither dosage of CY altered the suppression mediated by unseparated or nylon wool-adherent spleen cells. Furthermore, the administration of 50 mg of CY per kg failed to improve the depressed footpad responses of mice infected for 1 week to sheep erythrocytes in sheep erythrocyte-sensitized mice or to histoplasmin. These findings indicate that in experimental disseminated histoplasmosis, suppression effected by splenic T cells can be alleviated by CY; however, there is a persistent immunosuppressor mechanism(s) that cannot be counteracted by either indomethacin or CY.

Immunoregulation in disseminated histoplasmosis: characterization of the surface phenotype of splenic suppressor T lymphocytes

C57BL/6 and C3H/HeJ mice were infected intravenously with 6 X 10(5) yeast-phase Histoplasma capsulatum organisms. After 1 week, splenocytes from both mouse strains showed diminished antibody responses to sheep erythrocytes in vitro; these cells also were able to suppress the response of normal syngeneic cells. Passage of splenocytes from infected mice through a nylon wool column yielded a population enriched for T cells that exerted suppressor activity, although to a smaller extent than did unfractionated cells. Treatment of the T-cell-enriched population from both strains of mice with either anti-Thy 1.2 or anti-Ly 2 and complement resulted in a loss of this immunosuppressive ability. In addition, anti-I-Jk antiserum was effective in ablating the suppressive effect of C3H/HeJ nylon wool-passed spleen cells. The conclusion drawn from these experiments is that the T cells from H. capsulatum-infected animals which are capable of modulating the in vitro plaque-forming cell response to sheep erythrocytes bear Ly 2 and I-J determinants on their surfaces.

Aberrant immunoregulatory control of B lymphocyte function in lepromatous leprosy

The capacity of peripheral blood mononuclear (PBM) cells from patients with leprosy to generate immunoglobulin-secreting cells in response to pokeweed mitogen (PWM) was evaluated by a reverse haemolytic plaque forming cell (PFC) assay. The PFC responses of PBM cells from patients with lepromatous (Lpr) leprosy were significantly higher (P less than 0.01) than those of PBM cells from normal controls and patients with tuberculoid leprosy. Co-culture of T lymphocytes from normal donors with PBM cells from Lpr patients reduced the PFC response of these cells to the normal range. T4+-helper lymphocytes from Lpr donors did not induce supranormal responses to PWM by normal PBM cells enriched for B lymphocytes. T8+-suppressor lymphocytes from normal donors greatly reduced the response of cultures containing normal allogeneic B cells plus T4+ cells. Conversely, when T8+ cells from Lpr donors were cocultured with normal B cells plus T4+ cells, they failed to suppress the response to PWM. In summary, these studies have demonstrated abnormally high PWM-stimulated PFC responses by B lymphocytes from patients with Lpr leprosy. This aberration, in turn, is associated with a loss of regulatory function by T8+-suppressor cells in Lpr patients.

Comparison of 22 species of Mycobacteria by immunodiffusion against an absorbed reference leprosy serum

Lithium acetate antigenic extracts of 22 species of acetone-treated mycobacteria were tested by immunodiffusion precipitation for reactivity with a pool of sera from treated lepromatous leprosy patients (ARLS). This ARLS had been adsorbed with M. bovis (BCG, M. vaccae, cardiolipin, and lecithin to make it specific for M. leprae when used in an indirect immunofluorescence test. The ARLS produced two precipitin lines with M. leprae extract, one of which formed a line of identity with extracts of M. lepraemurium and M. bovis (BCG). Aso, recognition without reactions of identity was produced between ARLS and M. flavecens, M. gastri, M. gordonae, and M. nonchromogenicum. The ARLS did not recognize the 15 other species including the human pathogens, M. tuberculosis, M. intracellulare, M. kansasii, M. scrofulaceum, and M. marinum. These data suggest that serologic tests for M. leprae infection might be affected by antibodies to antigens shared by M. leprae and other mycobacteria. The significance of these shared antigens will depend upon the prevalence of human immune responses to mycobacteria containing the shared antigens in any given community.

Fatal reaction to dapsone during treatment of leprosy

A Burmese boy being treated with dapsone (diaminodiphenylsulfone [DDS]), 100 mg daily, for lepromatous leprosy had a fatal reaction to the drug 3 weeks after therapy was started. The clinical symptoms and progression of illness conform well to a "DDS syndrome" first described in the early 1950s. Although the syndrome clinically resembles infectious mononucleosis, neither Epstein-Barr virus nor cytomegalovirus was implicated as an etiologic agent in this case. The syndrome has been recognized during initiation of dapsone therapy for lepromatous leprosy and has led to the use of a prolonged induction period with initial dosages as low as 25 mg/week. However, because dapsone resistance has been recognized in some strains of Mycobacterium leprae, slow induction of therapy has been replaced with the schedule used for this patient. This report of a fatal reaction to dapsone emphasizes the need for caution when initiating therapy with the drug at full dosage.

Decreased suppressor cell activity in disseminated granulomatous infections

The effect of granulomatous infections upon the activity of a T lymphocyte subclass in human peripheral blood that can be induced by concanavalin A (Con A) to function in a suppressor mode was studied. Peripheral blood lymphocytes (PBL) from eleven patients with disseminated mycotic or mycobacterial infections or from controls were preincubated with and without Con A, washed and cultured with allogeneic PBL freshly drawn from healthy donors sensitive to histoplasmin. DNA synthesis was then measured in co-cultures stimulated by Con A, histoplasmin, or by the mixed lymphocyte culture (MLC) reaction alone. As compared with cells preincubated without Con A, the Con A-pretreated cells were significantly less effective in suppressing the responses of normal PBL to histoplasmin (P < 0.01), and in a one-way MLC reaction (P < 0.05). The Con A-induced suppressor activity of PBL from nine patients with localized granulomatous infections did not differ significantly from that exerted by PBL of normal controls in two of the three co-culture systems employed. These studies suggest that either dysfunction or a reduction of the Con A-inducible T-suppressor cell subpopulation in peripheral blood is frequent among patients was disseminated granulomatous infections.

Histoplasmosis. Association with circulating immune complexes, eosinophilia, and mesangiopathic glomerulonephritis

A patient with disseminated histoplasmosis, eosinophilia, and transient mesangiopathic glomerulonephritis stimulated a search for the presence of circulating immune complexes. Serum samples obtained on the fifth and 11th hospital days were strongly positive for ciculating immune complexes by both the Raji cell radioassay and the C1q solid phase assay. During the course of complete clinical recovery without therapy, both assays were weakly positive for circulating immune complexes on day 33. On day 56 they were negative. Using this case as a prototype, possible mechanisms for the renal immunopathology and the eosinophilic response are discussed with reference to the immunological perturbations thay may be observed in systemic mycotic infection.

Immunoregulatory responses in experimental disseminated histoplasmosis: lymphoid organ histopathology and serological studies

To study immunoregulatory mechanisms in systemic histoplasmosis, a highly reproducible model of infection was established in C3H/Anf mice. Intravenous inoculation of 6- to 8-week-old mice with from 5 x 10(5) to 10 x 10(5) cells of yeast-phase Histoplasma capsulatum strain G-217B produced disseminated infection that resolved over an 8-week period without therapeutic intervention. Serological studies demonstrated complement-fixing antibody production to yeast- and mycelial-phase antigens of H. capsulatum. Complement-fixing antibody to the former was detected at week 1, and it peaked at week 3 and declined thereafter. Complement-fixing antibody to mycelial-phase antigen(s) appeared later (week 3) and did not peak until week 18. Grossly, the spleens of infected mice were enlarged from three to four times normal size during peak infection, whereas the thymuses were markedly involuted. Conversely, at week 8 the average spleen size was considerably smaller and the thymic mass was increased relative to the mass at week 3. Histopathologically, the paracortical regions of lymph nodes and the white pulp (periarteriolar lymphocyte sheaths) and marginal zones of the spleen were heavily infiltrated by granulomata at week 1. By week 8, the infiltrates in these areas had largely resolved. Thymocytes were severely depleted from the cortical lobules of the thymus at week 1; however, thymic cellularity was restored by week 8. These reciprocal changes in cellularity of the thymus and spleen during active infection may be of importance with reference to the disturbances of immunoregulation that we have observed in Histoplasma-infected mice.

Immunoregulatory responses in experimental disseminated histoplasmosis: depression of T-cell-dependent and T-effectory responses by activation of splenic suppressor cells

The cellular immune responses of mice with disseminated histoplasmosis are markedly diminished in association with the generation of potent immunosuppressor activity by spleen cells. The zenith of suppressor activity was observed during most active infection, from 1 to 3 weeks after inoculation. During this time there was: (i) depression of the delayed-type hypersensitivity response to sheep erythrocytes and histoplasmin, (ii) impairment of concanavalin A- and histoplasmin-induced blastogenic transformations by splenocytes in vitro, (iii) depressed cytotoxic activity of spleen cells from infected mice, and (iv) marked suppression by splenocytes from infected mice of the primary antibody response to sheep erythrocytes by normal spleen cell cultures. With resolution of the infection by week 8, there was a shift of immunoregulatory function from dominant suppressor activity to expression of helper activity. At this time, delayed-type hypersensitivity responses to the above antigens were vigorous; furthermore, the cytotoxic activity and plaque-forming cell response of splenocytes from 8-week-infected mice were equal to or greater than normal control values. The shift in the immunoregulatory response from a suppressor to a helper mode indicated that the net amount of help or suppression measured at any given time during infection represented the algebraic sum of both helper and suppressor activities mediated by different populations or subpopulations of cells within the splenic microenvironment of infected mice.

The evolution of immunosuppressive cell populations in experimental mycobacterial infection

Immunosuppressor activity of considerable potency and complexity was generated during the course of chronic, progressive infection of C3H/Anf mice by Mycobacterium lepraemurium. From the 5th through 10th week after inoculation, spleen cells from infected mice mildly but reproducibly suppressed the direct plaque-forming cell response of normal spleen cell cultures to sheep erythrocytes. Suppression at this stage of infection was mediated by cells with macrophage-like characteristics. A marked increase in splenic suppressor activity at 10 to 11 weeks was associated with the appearance of a second suppressor cell subpopulation composed of T lymphocytes. The appearance of these cells was closely related in time to the onset of rapid splenic enlargement and a loss of cutaneous delayed type hypersensitivity to antigens of M. lepraemurium in mice at 10 to 11 weeks of infection. Suppressor cells were not present in peripheral lymph nodes until terminal infection at 22 to 25 weeks. Suppressor spleen cells depressed the T-dependent antibody response most severely, but there was also a direct effect upon B cells as shown by moderate suppression of responses to TNP-LPS and DNP-Ficoll. Spleen cells from 14-week-infected mice generated a soluble suppressor factor(s) that induces depression of moderate severity, however, the immunosuppression by intact cells was far greater.