Capsulatum Yeast Research Articles

Inhibition of growth of Histoplasma capsulatum yeast cells in human macrophages by the iron chelator VUF 8514 and comparison of VUF 8514 with deferoxamine.

Histoplasma capsulatum requires intracellular iron to survive and multiply within human and murine macrophages (M phi). Thus, iron chelators may be useful compounds in the treatment of histoplasmosis. In the present study we compared the efficacies of five different iron chelators with deferoxamine (DEF) for their capacity to inhibit the growth of H. capsulatum yeast cells in culture medium and within human M phi. Of the agents tested, only one, VUF 8514, a 2,2'-bipyridyl analog, was found to be effective. VUF 8514 inhibited the growth of yeast cells in tissue culture medium and within M phi in a dose-response fashion. In tissue culture medium, the 50% effective dose (ED50) of VUF 8514 was 30 nM and the ED50 of DEF was 1 mM. In human M phi, the ED50 of VUF 8514 was 520 nM and the ED50 of DEF was 4 mM. Thus, VUF 8514 was effective at a concentration 7.7 x 10(3)-fold lower than DEF in inhibiting the growth of yeast cells in M phi. Inhibition of the intracellular growth of yeast cells by VUF 8514 was reversed by holotransferrin and iron nitriloacetate, an iron compound that is soluble at neutral to alkaline pH. Thus, VUF 8514 inhibits the intracellular growth of yeast cells by acting as an iron chelator rather than through its capacity as a weak base. These data suggest that the hydroxamic acid siderophore of H. capsulatum yeast cells competes successfully for iron against some iron chelators but not others and that VUF 8514 may be a potential therapeutic agent for the treatment of histoplasmosis.

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.

Impaired responsiveness to gamma interferon of macrophages infected with lymphocytic choriomeningitis virus clone 13: susceptibility to histoplasmosis

Lymphocytic choriomeningitis virus clone 13 (LCMV clone 13), a variant isolated from the spleens of neonatally infected mice, causes persistent infections in mice infected as adults. Such persistently infected mice succumb to a normally sublethal dose of Histoplasma capsulatum, and their macrophages contain overwhelming numbers of yeast cells of the fungus. Both LCMV clone 13 and H. capsulatum yeast cells target and replicate in macrophages of the host. We sought to study the effects of LCMV clone 13 on the ability of macrophages to control growth of H. capsulatum in vitro. We show that the growth of H. capsulatum within macrophages was not directly affected by the presence of LCMV clone 13. However, macrophages containing LCMV clone 13 did not respond fully to gamma interferon (IFN-gamma) stimulation. Such unresponsiveness resulted in proliferation of the fungus within macrophages cultured in the presence of IFN-gamma. The addition of anti-IFN-alpha/beta antibodies to LCMV clone 13-infected macrophage cultures restored macrophage responsiveness to IFN-gamma. These results indicate that production of IFN-alpha/beta by LCMV clone 13-infected macrophages antagonizes their responsiveness to IFN-gamma. Such antagonism may be one of the mechanisms by means of which certain viruses cause immune suppression and susceptibility to opportunistic infections.

Efficacy of the triazole D0870 in a murine model of systemic histoplasmosis

The efficacy of D0870 was studied in a murine model of systemic histoplasmosis and was compared with that of fluconazole. All regimens of D0870 (1 or 10 mg/kg of body weight given daily or 1, 10, or 100 mg/kg given every other day) and 100 mg of fluconazole per kg given daily provided complete protection from lethality. Comparison of the number of viable Histoplasma capsulatum yeasts remaining in the spleen or liver indicated that D0870 was superior to fluconazole in clearing and curing infection. D0870 was 10- to 100-fold more efficacious than fluconazole in the treatment of experimental histoplasmosis.

Macrophages from human immunodeficiency virus-positive persons are defective in host defense against Histoplasma capsulatum.

The phagocytic and fungistatic activity of monocyte-derived macrophages from human immunodeficiency virus (HIV)-positive persons against Histoplasma capsulatum yeasts was determined. Macrophages from HIV-positive patients were profoundly deficient in their capacity to recognize and bind H. capsulatum, but ingestion of bound yeasts was normal. The binding of H. capsulatum by patient macrophages tended to decrease with a decrease in CD4+ T lymphocyte counts. Another major defect was that patient macrophages were more permissive for the intracellular growth of H. capsulatum. Macrophages from 22 of 58 patients showed a > or = 2-fold increase in intracellular growth compared with control macrophages. Thus, in addition to defects in cell-mediated immunity caused by a loss of CD4+ T cells, macrophages from HIV-positive patients exhibit intrinsic defects in macrophage function against H. capsulatum that may contribute to the increased susceptibility of HIV-positive patients to disseminated histoplasmosis.

Chloroquine induces human macrophage killing of Histoplasma capsulatum by limiting the availability of intracellular iron and is therapeutic in a murine model of histoplasmosis.

We investigated the role of intracellular iron on the capacity of Histoplasma capsulatum (Hc) yeasts to multiply within human macrophages (Mphi). Coculture of Hc-infected Mphi with the iron chelator deferoxamine suppressed the growth of yeasts in a concentration-dependent manner. The effect of deferoxamine was reversed by iron-saturated transferrin (holotransferrin) but not by iron-free transferrin (apotransferrin). Chloroquine, which prevents release of iron from transferrin by raising endocytic and lysosomal pH, induced human Mphi to kill Hc. The effect of chloroquine was reversed by iron nitriloacetate, an iron compound that is soluble at neutral to alkaline pH, but not by holotransferrin, which releases iron only in an acidic environment. Chloroquine (40-120 mg/kg) given intraperitoneally for 6 d to Hc-infected C57BL/6 mice significantly reduced the growth of Hc in a dose-dependent manner. At 120 mg/kg there was a 17- and 15-fold reduction (P < 0.01) in CFU in spleens and livers, respectively. The therapeutic effect of chloroquine also correlated with the length of treatment. As little as 2 d of chloroquine therapy (120 mg/kg), when started at day 5 after infection, reduced CFU in the spleen by 50%. Treatment with chloroquine for 10 d after a lethal inoculum of Hc protected six of nine mice; all control mice were dead by day 11 (P = 0.009). This study demonstrates that: (a) iron is of critical importance to the survival and multiplication of Hc yeasts in human Mphi; (b) in vitro, chloroquine induces Mphi killing of Hc yeasts by restricting the availability of intracellular iron; and (c) in vivo, chloroquine significantly reduces the number of organisms in the spleens and livers of Hc-infected mice and can protect mice from a lethal inoculum of Hc yeasts. Thus, chloroquine may be effective in the treatment of active histoplasmosis and also may be useful in preventing relapse of histoplasmosis in patients with acquired immunodeficiency syndromes.

Recombinant murine gamma interferon stimulates macrophages of the RAW cell line to inhibit intracellular growth of Histoplasma capsulatum.

Macrophages of the RAW 264.7 cell line, activated by pretreatment with recombinant murine gamma interferon, inhibit the intracellular growth of Histoplasma capsulatum. Growth inhibition occurred by a mechanism that was operative only when L-Arg metabolism was allowed to occur. When activated macrophages were cultured in the absence of L-Arg or in the presence of NG-monomethyl-L-Arg, a competitive inhibitor of L-Arg metabolism, activation to the antihistoplasma growth-inhibitory state did not occur. An increase in levels of NO2-, an end product of L-Arg metabolism, was detected only after activation of RAW 264.7 cells to the growth-inhibitory state. In contrast, only baseline levels of NO2- were detected when L-Arg was excluded or when NG-monomethyl-L-Arg was added to the culture medium. Nitric oxide (NO.), a reactive intermediate product of L-Arg metabolism, was implicated as the relevant antihistoplasma effector molecule. When H. capsulatum yeast cells were cultured for 24 to 28 h in a system designed to generate soluble NO., a dose-dependent cytotoxic effect was observed.

Local immunity in lung-associated lymph nodes in a murine model of pulmonary histoplasmosis.

Local immunity against acute pulmonary histoplasmosis was studied in the lung-associated lymph nodes of normal nonimmune mice infected intratracheally with live Histoplasma capsulatum yeasts. The phenotypes and distribution of cells in lung-associated lymph nodes and spleens were determined by flow cytometry. In addition, the immune responsiveness of these cells was evaluated by in vitro blastogenesis. Anti-H. capsulatum antibodies in serum and H. capsulatum antigen in tissue were measured by immunoassays. Cellular immune responses were greater in the lymph nodes than in the spleens. In lymph nodes 7 days after infection, a marked increase in the number of B lymphocytes caused the percentage to rise to 43%, compared with 26% in controls, and it remained elevated throughout the course of infection. A CD3+ cell that did not express CD4 or CD8 increased in number until it constituted 21% of lymph node cells, compared with 5% in controls, by day 14. The numbers of CD4+ and CD8+ T lymphocytes were modestly increased from days 7 to 35, but their percentages dropped because of the greater numbers of B lymphocytes and CD3+4-8- cells. Macrophages consistently constituted 2 to 3% of lymph node cells during the study. In spleens 7 days after infection, the percentage of macrophages in infected mice rose to 21%, compared with 9% in controls, but the total spleen cell number did not increase until day 14, when all cell subsets were nearly double in number. The in vitro blastogenic response of lymph node cells to H. capsulatum peaked at day 7, but spleen cell response was minimal during the course of infection. Histoplasma-specific serum immunoglobulin G antibodies reached peak levels by day 21 and remained high to the end of the study. In contrast, levels of antigen-specific immunoglobulin M antibodies were very low. These data suggest that antigen-specific immune responses occur in lung-associated lymph nodes and that this draining lymph node response may be an important component in host defense against Histoplasma lung infection.

Human neutrophil-mediated fungistasis against Histoplasma capsulatum. Localization of fungistatic activity to the azurophil granules.

Human neutrophils (PMN) demonstrated potent fungistatic activity against Histoplasma capsulatum (Hc) yeasts in a sensitive microassay that quantifies the growth of yeasts by the incorporation of [3H]leucine. At a PMN:yeast ratio of 1:2, PMN inhibited the growth of yeasts by 37%. Maximum inhibition of 85% to 95% was achieved at a PMN/yeast ratio of 10:1 to 50:1. Opsonization of the yeasts in fresh or heat-inactivated serum was required for PMN-mediated fungistasis, but ingestion of the yeasts was not required. Recognition and phagocytosis of opsonized yeasts was via PMN complement receptor (CR) type 1 (CR1), CR3, and FcRIII (CD16). PMN fungistatic activity was evident by 2 h, was maximum at 24 h, and persisted up to 5 d. In contrast, yeasts multiplied within monocytes to a greater extent than in culture medium alone. PMN from three patients with chronic granulomatous disease (CGD) inhibited the growth of Hc yeasts by an average of 97%, compared with 86% in three normal controls. Furthermore, preincubation of PMN with the lysosomotropic agent NH4Cl inhibited fungistatic activity in a concentration-dependent manner. Finally, experiments with subcellular fractions of PMN demonstrated that the principal component of the fungistatic activity of PMN was localized in the azurophil granules. These data demonstrate that human PMN possess potent fungistatic activity against Hc yeasts and further show that fungistasis is mediated by antimicrobial agents contained in the azurophil granules.

Histoplasma capsulatum modulates the acidification of phagolysosomes.

The phagolysosome is perhaps the most effective antimicrobial site within macrophages due both to its acidity and to its variety of hydrolytic enzymes. Few species of pathogens survive and multiply in these vesicles. However, one strategy for microbial survival would be to induce a higher pH within these organelles, thus interfering with the activity of many lysosomal enzymes. Altering the intravesicular milieu might also profoundly influence antigen processing, antimicrobial drug delivery, and drug activity. Here we report the first example of an organism proliferating within phagolysosomes that maintain a relatively neutral pH for a sustained period of time. We inoculated P388D1 macrophages with fluorescein isothiocyanate (FITC)-labeled Histoplasma capsulatum or zymosan. Using the ratio of fluorescence excitations at 495 and 450 nm, we determined that vesicles containing either virulent or avirulent FITC-labeled H. capsulatum yeasts had a pH one to two units higher than vesicles containing either zymosan or methanol-killed H. capsulatum. The difference in pH remained stable for at least 5.5 h postinoculation. Longer-term studies using cells preincubated with acridine orange indicated that phagolysosomes containing live Histoplasma continued to maintain a relatively neutral pH for at least 30 h. Many agents raise the pH of multiple vesicles within the same cell. In contrast, H. capsulatum affects only the phagolysosome in which it is located; during coinoculation of cells with unlabeled Histoplasma and labeled zymosan, organelles containing zymosan still acidified normally. Similarly, unlabeled zymosan had no influence on the elevated pH of vesicles housing labeled Histoplasma. Thus, zymosan and Histoplasma were segregated into separate phagolysosomes that responded independently to their phagocytized contents. This localized effect might reflect an intrinsic difference between phagosomes housing the two particle types, active buffering by the microbe, or altered ion transport across the phagolysosomal membrane such that acidification is inhibited.

Histoplasma capsulatumand Vβamice: cellular immune responses and susceptibility patterns

Certain strains of mice, designated V beta a, have a deletion of the gene segments encoding the beta chain of the T-cell receptor variable region. These mice do not express 40 to 50% of the T-cell receptor V beta chains. In this study, we examined the influence of this deletion on susceptibility to Histoplasma capsulatum. In addition, H. capsulatum-injected V beta a mice were tested for their capacity to generate T-cell dependent responses to H. capsulatum antigens. Susceptibility profiles of V beta a mice, SWR/J (H-2q), SJL/J (H-2s) and C57L-(H-2b), were compared to V beta b strains, C57BL/6 (H-2b) and DBA/l (H-2q), following intravenous (IV) injection of sublethal and lethal inocula of H. capsulatum yeast cells. One week after injection of 6 x 10(5) yeast cells, the spleens of SWR/J, SJL/J and C57L mice contained 5- to 7-fold fewer colony forming units (CFU) than spleens of C57BL/6 mice. Approximately 50% fewer CFU of H. capsulatum were recovered from the spleens of DBA/l mice compared to those from C57BL/6 animals. Subsequently, groups of mice were challenged IV with either 1.5 x 10(7) or 7.5 x 10(6) yeast cells and observed for 30 days. Survival of SWR/J,SJL/J, C57L and DBA/l mice was significantly prolonged compared to C57BL/6 mice. V beta a and DBA/l mice injected with viable H. capsulatum yeast cells mounted a delayed-type hypersensitivity response to an extract from the cell wall and cell membrane of yeast cells and to HIS-62, a purified antigen derived therefrom.(ABSTRACT TRUNCATED AT 250 WORDS)

Colony-stimulating factors activate human macrophages to inhibit intracellular growth of Histoplasma capsulatum yeasts.

Recombinant cytokines and colony-stimulating factors (CSFs) were tested for their abilities to activate human monocytes/macrophages (M phi) to inhibit the intracellular growth of or kill Histoplasma capsulatum yeasts. None of the cytokines or CSFs or combinations of cytokines and CSFs activated M phi fungistatic activity when they were added to M phi monolayers concurrently with yeasts. In contrast, culture of monocytes for 7 days in the presence of interleukin 3, granulocyte-M phi CSF, or M phi CSF stimulated M phi fungistatic (but not fungicidal) activity against H. capsulatum yeasts in a concentration-dependent manner. Optimal activation of M phi by CSFs required 5 days of coculture, and the cultures had to be initiated with freshly isolated peripheral blood monocytes. Culture of monocytes with combinations of CSFs or addition of CSFs during the 24 h of coculture with the yeasts did not further enhance M phi fungistatic activity for H. capsulatum. Addition of gamma interferon or tumor necrosis factor alpha to CSF-activated M phi also did not enhance M phi fungistatic activity. These results suggest that interleukin 3, granulocyte-M phi CSF, and M phi CSF may play a role in the cell-mediated immune response to H. capsulatum by enhancing monocyte/M phi fungistatic activity.

Digestion of histoplasma capsulatum yeasts by human macrophages

Digestion of histoplasma capsulatum yeasts by human macrophages

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.

Alterations in murine macrophage arachidonic acid metabolism following ingestion of nonviable Histoplasma capsulatum.

The effect of ingestion of heat-killed Histoplasma capsulatum yeast cells on the metabolism of arachidonic acid (20:4) to prostenoids and leukotrienes was examined in murine peritoneal macrophages (M phi s). H. capsulatum-containing M phi s exhibited a metabolite profile similar to that of zymosan-challenged phagocytes; however, there were differences with respect to the relative and total amounts of products produced. While proteose peptone-elicited M phi s exposed to H. capsulatum released quantitatively less prostaglandin E2 (PGE2) and leukotriene C4 than zymosan-treated M phi s, they metabolized a greater percentage of total product to prostenoids. In addition, whereas in vitro priming with gamma interferon increased both the PGE2 and leukotriene C4 contents of zymosan-stimulated M phi supernatants, similarly primed M phi s challenged with H. capsulatum selectively increased only PGE2 production. The immunosuppressive effect of a relative excess of prostenoids in H. capsulatum-containing M phi s may contribute to the overall disturbance in cell-mediated immunity characteristic of disseminated histoplasmosis.

Inhibition of murine macrophage protein kinase C activity by nonviable Histoplasma capsulatum.

Ingestion of Histoplasma capsulatum yeast cells inhibits the oxidative burst response of murine macrophages (M phi's). Since protein kinase C (PKC) is believed to be an integral part of the signal transduction pathway involved in the production of reactive oxygen intermediates, we investigated the relationship between PKC activity and oxidative burst inhibition in H. capsulatum-containing murine peritoneal M phi's. An inhibitory effect on both basal and phorbol myristate acetate-mobilized membrane PKC activities was observed in M phi's which had ingested H. capsulatum but not latex spheres. These results suggest that one way in which H. capsulatum may disrupt the oxidative burst is through a PCK-dependent mechanism.

Recognition of Histoplasma capsulatum yeast-cell antigens by human lymphocytes and human T-cell clones.

We have prepared a detergent extract from the cell wall and cell membrane of Histoplasma capsulatum yeast cells that is recognized by T cells from mice immunized with viable organisms or with the extract. A 62-kd antigen from this extract has been isolated and has been shown to be antigenic and to confer protective immunity in mice. In this study, we examined the in vitro proliferative response by human lymphocytes and human T-cell clones to both the extract from the cell wall and cell membrane and the 62-kd antigen, termed HIS-62. Seven healthy individuals were identified whose peripheral blood mononuclear cells responded to the cell wall and cell membrane extract from H. capsulatum yeast cells. Mononuclear cells from all seven individuals recognized histoplasmin. T-cell clones were generated from peripheral blood mononuclear cells from a single person using the extract from cell wall and cell membrane as the antigenic preparation. Nineteen clones were propagated; all expressed the surface phenotype CD3+, CD4+, T-cell receptor alpha/beta +. The clones were antigen-specific. Of 17 clones studied, none responded to extracts from Blastomyces dermatitidis or Coccidioides immitis or to tetanus toxoid. Sixteen of 19 clones recognized HIS-62 in vitro. Additional analysis revealed that cells from each of the seven individuals who responded to the extract mounted a proliferative response to HIS-62. Thus, the extract from the cell wall and cell membrane and HIS-62 are targets of the human cell-mediated immune response to H. capsulatum. Moreover, HIS-62 appears to be an immunodominant antigen.

Chronic Histoplasma capsulatum Infection of the Central Nervous System Successfully Treated with Fluconazole

A 48-year-old man with a long-standing history of communicating hydrocephalus is reported. Ventriculoperitoneal shunting led to clinical improvement, but symptoms recurred despite surgical re-exploration switching the shunt to an atrial drainage. Ten months after the last surgical procedure, an acute myelopathy developed. Concomitant pharyngeal granuloma examination identified Histoplasma capsulatum (Hc) yeasts. Despite initial response to amphotericin B, Hc was isolated from cerebrospinal fluid (CSF), valve reservoir and distal catheter after two courses of therapy. Fluconazole successfully sterilized CSF, but transverse myelopathy persisted unchanged, and shunting was needed to control hydrocephalus.

Protective efficacy of a 62-kilodalton antigen, HIS-62, from the cell wall and cell membrane of Histoplasma capsulatum yeast cells

We reported previously that a detergent extract of the cell wall and cell membrane of Histoplasma capsulatum yeast cells contains antigens recognized by T cells. In T-cell immunoblot analysis, a region encompassing 62 kDa was stimulatory for an H. capsulatum-reactive T-cell line and T-cell clones derived from C57BL/6 mice. In this study, we isolated a 62-kDa band, termed HIS-62, from electrophoresed cell wall and cell membrane of H. capsulatum yeast cells and examined its antigenicity and immunogenicity. C57BL/6, BALB/c, and CBA/J mice that were immunized with viable H. capsulatum yeast cells mounted a delayed-type hypersensitivity response to HIS-62 that was stronger than that of normal controls. Spleen cells from each strain of mouse immunized with viable yeast cells proliferated vigorously in response to HIS-62; conversely, splenocytes from control animals did not recognize this antigen. A T-cell line and 5 of 5 T-cell clones from C57BL/6 mice, 10 of 15 BALB/c T-cell hybridomas, and 8 of 12 CBA/J T-cell hybridomas recognized HIS-62. A cutaneous delayed-type hypersensitivity response to the antigen was apparent in each strain of mouse that was injected with 80 micrograms of HIS-62 mixed with Freund adjuvant. In addition, spleen cells from HIS-62-immunized mice proliferated in vitro in response to this antigen. Vaccination of each strain of mouse with 80 micrograms of HIS-62 conferred protection against a lethal intravenous challenge with H. capsulatum yeast cells. Thus, HIS-62 appears to be an important target of the cellular immune response to H. capsulatum and induces a protective immune response in mice.

Deficiency in the incorporation of labeled thymidine and inhibition in the biosynthesis of interleukin-2 in lymphocytes obtained from Histoplasma capsulatum infected mice

The incorporation of (3H) thymidine and the biosynthesis of interleukin-2(IL-2) were investigated in Concanavalin A (ConA) and histoplasmin stimulated lymphocytes from spleen of infected Balb/c mice with the yeast phases of Histoplasma capsulatum. The ability to incorporate (3H) thymidine of Con A stimulated lymphocytes in culture from spleen of Histoplasma capsulatum infected mice, as well as the IL-2 content present in the supernatants of that cultures, were depressed along the first three weeks of the experiments, but starting week five, normal values were restored or even discretly increased. Incorporation of (3H) thymidine in histoplasmin stimulated lymphocytes remained inhibited along the seven weeks the experiment lasted. Results showed that inoculation of H. capsulatum yeast in mice provoked a temporary immunosuppression on cell mediated immunity, that can be explained by means of the inability of T cells to produce enough IL-2 necessary for the proliferation of T cells in culture.