Herpes zoster-related deaths in the United States: validity of death certificates and mortality rates, 1979-2007

BACKGROUND

Herpes zoster (HZ) vaccine was recommended in the United States to reduce HZ-associated morbidity. Vaccination may reduce HZ-associated mortality, but no strategy exists to monitor mortality trends.

METHODS

We validated HZ coding on death certificates from California, using hospital records as the gold standard, and applied the results to national-level data to estimate HZ mortality.

RESULTS

In the validation phase of the study, among 40 available hospital records listing HZ as the underlying cause of death, HZ was the underlying cause for 21 (52.5%) and a contributing cause for 5 (12.5%). Among the 21 hospital records listing HZ as the underlying cause of death, the median age of decedents was 84 years (range, 50-99); 60% had no contraindications for HZ vaccination. Of the 37 available records listing HZ as a contributing cause of death, HZ was a contributing cause for 2 (5.4%) and the underlying cause for 6 (16.2%). Nationally, in the 7 years preceding the HZ vaccination program, the average annual number of deaths in which HZ was reported as the underlying cause of death was 149; however, based on our validation study, we estimate the true number was 78 (range, 31-118).

CONCLUSIONS

National death certificate data greatly overestimate deaths in which HZ is the underlying or contributing cause of death. The HZ vaccination program could prevent some HZ-related deaths, but the impact will be difficult to assess using national mortality data.

Evidence of Borrelia autoimmunity-induced component of Lyme carditis and arthritis

We investigated the possibility that manifestations of Lyme disease in certain hosts, such as arthritis and carditis, may be autoimmunity mediated due to molecular mimicry between the bacterium Borrelia burgdorferi and self-components. We first compared amino acid sequences of Streptococcus pyogenes M protein, a known inducer of antibodies that are cross-reactive with myosin, and B. burgdorferi and found significant homologies with OspA protein. We found that S. pyogenes M5-specific antibodies and sera from B. burgdorferi-infected mice reacted with both myosin and B. burgdorferi proteins by Western blots and enzyme-linked immunosorbent assay. To investigate the relationship between self-reactivity and the response to B. burgdorferi, NZB mice, models of autoimmunity, were infected. NZB mice infected with B. burgdorferi developed higher degrees of joint swelling and higher anti-B. burgdorferi immunoglobulin M cross-reactive responses than other strains with identical major histocompatibility complex (DBA/2 and BALB/c). These studies reveal immunological cross-reactivity and suggest that B. burgdorferi may share common epitopes which mimic self-proteins. These implications could be important for certain autoimmunity-susceptible individuals or animals who become infected with B. burgdorferi.

Role of Fc gamma receptors in triggering host cell activation and cytokine release by Borrelia burgdorferi

Borrelia burgdorferi, the spirochetal bacterium that causes human Lyme disease, encodes numerous lipoproteins which have the capacity to trigger the release of proinflammatory cytokines from a variety of host cell types, and it is generally believed that these cytokines contribute to the disease process in vivo. We previously reported that low-passage-number infectious B. burgdorferi spirochetes express a novel lipidation-independent activity which induces secretion of the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) by the mouse MC/9 mast cell line. Using RNase protection assays, we determined that mast cells exposed in vitro to low-passage-number, but not high-passage-number, B. burgdorferi spirochetes show increased expression of additional mRNAs representing several chemokines, including macrophage-inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, and TCA3, as well as the proinflammatory cytokine interleukin-6. Furthermore, mast cell TNF-alpha secretion can be inhibited by the phosphatidylinositol 3-kinase inhibitor wortmannin and also by preincubation with purified mouse immunoglobulin G1 (IgG1) and IgG2a, but not mouse IgG3, and by a mouse Fc gamma receptor II and III (FcgammaRII/III)-specific rat monoclonal antibody, suggesting the likely involvement of host FcgammaRIII in B. burgdorferi-mediated signaling. A role for passively adsorbed rabbit or bovine IgG or serum components in B. burgdorferi-mediated FcgammaR signaling was excluded in control experiments. These studies confirm that low-passage-number B. burgdorferi spirochetes express a novel activity which upregulates the expression of a variety of host cell chemokine and cytokine genes, and they also establish a novel antibody-independent role for FcgammaRs in transduction of activation signals by bacterial products.

Trypanosoma cruzi: roles for perforin-dependent and perforin-independent immune mechanisms in acute resistance

CD8+ T cells have been shown to be required for acute resistance to infection with the protozoan parasite, Trypanosoma cruzi, the causative agent of Chagas' disease. However, to date, the mechanism by which CD8+ T cells mediate protection in vivo has not been determined. While CD8+ T cells can exhibit cytolytic function, they also secrete cytokines such as IFN-gamma, which is known to mediate protection against T. cruzi infections. To determine whether cytolysis is an important effector function in vivo, we have compared outcomes of T. cruzi infection in normal and perforin-deficient mice. Our results indicate that while perforin-dependent cytolytic mechanisms clearly make a major contribution to acute resistance to T. cruzi infection, this contribution may be strain and challenge dose-dependent, since perforin-deficient mice challenged with lower doses of a less virulent strain survived and were subsequently resistant to challenge with virulent organisms. In vivo depletion studies demonstrated that survival of perforin-deficient mice challenged with low doses of T. cruzi requires both CD4+ and CD8+ T cells and is dependent on IFN-gamma secretion. These studies document the participation of both perforin-dependent cytotoxic and perforin-independent, IFN-gamma-dependent immune mechanisms in acute resistance to T. cruzi infection.

Borrelia burgdorferi spirochetes induce mast cell activation and cytokine release

The Lyme disease spirochete, Borrelia burgdorferi, is introduced into human hosts via tick bites. Among the cell types present in the skin which may initially contact spirochetes are mast cells. Since spirochetes are known to activate a variety of cell types in vitro, we tested whether B. burgdorferi spirochetes could activate mast cells. We report here that freshly isolated rat peritoneal mast cells or mouse MC/9 mast cells cultured in vitro with live or freeze-thawed B. burgdorferi spirochetes undergo low but detectable degranulation, as measured by [5-3H] hydroxytryptamine release, and they synthesize and secrete the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha). In contrast to findings in previous studies, where B. burgdorferi-associated activity was shown to be dependent upon protein lipidation, mast cell TNF-alpha release was not induced by either lipidated or unlipidated recombinant OspA. This activity was additionally shown to be protease sensitive and surface expressed. Finally, comparisons of TNF-alpha-inducing activity in known low-, intermediate-, and high-passage B. burgdorferi B31 isolates demonstrated passage-dependent loss of activity, indicating that the activity is probably plasmid encoded. These findings document the presence in low-passage B. burgdorferi spirochetes of a novel lipidation-independent activity capable of inducing cytokine release from host cells.

Recombinant IL-4 treatment augments resistance to Borrelia burgdorferi infections in both normal susceptible and antibody-deficient susceptible mice

Recent evidence suggests that T cells and their associated cytokines critically influence outcome in mice experimentally infected with Borrelia burgdorferi (Bb), the causative agent of human Lyme disease. In vivo T cell subset and cytokine depletion studies suggest that CD4+ T cell-derived IL-4 plays a critical role in control of spirochete growth in vivo, whereas CD8+ T cell-derived IFN-gamma appears to promote disease, particularly in susceptible mouse strains. To further investigate the immunologic basis of protection and the role of IL-4, we have examined the effects of early rIL-4 treatment on outcome in susceptible mice infected with Bb. In this study, we show that administration of rIL-4 to susceptible C3H mice during the first week of infection with Bb leads to early control of their infections, as evidenced by significant reductions in joint swelling at wk 5, 6, and 7 postinfection, and in the numbers of spirochetes recovered from their joints and skin at wk 7 when compared with sham-treated mice. Increased resistance in rIL-4-treated mice was accompanied by significant reductions in their in vitro splenic Bb-specific IFN-gamma responses and in serum levels of specific IgG2a and IgG3 Abs and significant increases in specific IgG1 Abs. We also show that the inherent susceptibility of Ab-deficient, C57BL/6-IgM knockout (B6-MKO) mice to Rh infection is intermediate relative to C57BL/6 severe combined immunodeficient (B6-SCID) mice (susceptible) or normal C57BL/6 mice (resistant), confirming the importance of both Ab-dependent and Ab-independent, T cell-dependent immune mechanisms in control of Bb infections. The additional finding that early treatment with rIL-4 significantly reduced the severity of Bb infections in B6-MKO mice indicates that IL-4 may augment anti-spirochetal immunity via an Ab-independent mechanism.

Recombinant IL-4 treatment augments resistance to Borrelia burgdorferi infections in both normal susceptible and antibody-deficient susceptible mice

Recent evidence suggests that T cells and their associated cytokines critically influence outcome in mice experimentally infected with Borrelia burgdorferi (Bb), the causative agent of human Lyme disease. In vivo T cell subset and cytokine depletion studies suggest that CD4+ T cell-derived IL-4 plays a critical role in control of spirochete growth in vivo, whereas CD8+ T cell-derived IFN-gamma appears to promote disease, particularly in susceptible mouse strains. To further investigate the immunologic basis of protection and the role of IL-4, we have examined the effects of early rIL-4 treatment on outcome in susceptible mice infected with Bb. In this study, we show that administration of rIL-4 to susceptible C3H mice during the first week of infection with Bb leads to early control of their infections, as evidenced by significant reductions in joint swelling at wk 5, 6, and 7 postinfection, and in the numbers of spirochetes recovered from their joints and skin at wk 7 when compared with sham-treated mice. Increased resistance in rIL-4-treated mice was accompanied by significant reductions in their in vitro splenic Bb-specific IFN-gamma responses and in serum levels of specific IgG2a and IgG3 Abs and significant increases in specific IgG1 Abs. We also show that the inherent susceptibility of Ab-deficient, C57BL/6-IgM knockout (B6-MKO) mice to Rh infection is intermediate relative to C57BL/6 severe combined immunodeficient (B6-SCID) mice (susceptible) or normal C57BL/6 mice (resistant), confirming the importance of both Ab-dependent and Ab-independent, T cell-dependent immune mechanisms in control of Bb infections. The additional finding that early treatment with rIL-4 significantly reduced the severity of Bb infections in B6-MKO mice indicates that IL-4 may augment anti-spirochetal immunity via an Ab-independent mechanism.

Trypanosoma cruzi: exposure of murine cells to live parasites in vitro leads to enhanced surface class I MHC expression which is type I interferon-dependent

Previous reports indicate that myocardial cells from human patients with chronic Chagasic cardiomyopathy express increased levels of class I MHC molecules on their surfaces. To determine whether parasites can modulate class I expression, we have examined the effect of in vitro exposure to live Trypanosoma cruzi trypomastigotes on class I MHC expression by murine cells. Here we show that co-incubation of various murine cell lines, including 3T3 fibroblasts, J774.A1 macrophage-like cells, and freshly-explanted BALB/c primary embryo fibroblasts, with live trypomastigotes leads to a two- to fourfold increase in their expression of surface class I MHC molecules. Cell-free supernatants from T. cruzi-exposed cells, but not from either cells or parasites cultured alone, were also capable of upregulating class I expression, indicating the involvement of a soluble factor. Active supernatants were shown to contain IFN-alpha/beta activity and their ability to upregulate class I was inhibitable by anti-IFN-alpha/beta Abs. This ability of T. cruzi to enhance class I MHC expression on host cells via IFN-alpha/beta induction could be an important factor in the initiation of host immunity and/or immune-mediated pathology.

Role of IL-4 and IFN-gamma in modulation of immunity to Borrelia burgdorferi in mice

Because T cells appear to modulate the severity of murine Borrelia burgdorferi infections, we decided to examine the possible involvement of T cell-associated cytokines in disease outcome. Comparison of in vitro B. burgdorferi Ag-induced cytokine production in disease-susceptible and -resistant strains revealed striking differences; spleen cells from susceptible C3H mice produced significantly higher levels of IL-2 and IFN-gamma and lower levels of IL-4 than spleen cells from resistant BALB/c mice. Lymph node responses were even more divergent, with C3H mice producing high levels of IFN-gamma, and BALB/c mice producing little or none. This apparent Th1/Th2 cytokine imbalance was also reflected in vivo, since serum from C3H had significantly higher levels of B. burgdorferi-specific IgG2a Ab and lower levels of IgG1 Ab than serum from BALB/c mice. In vivo studies confirmed the importance of IL-4 in early control of spirochete growth, since treatment of either strain with neutralizing anti-IL-4 mAb led to increased joint swelling and higher spirochete burdens in joints compared with those in control mAb-treated mice. In contrast, IFN-gamma may hinder early control of spirochete growth in susceptible C3H mice, since treatment of mice with neutralizing anti-IFN-gamma mAb reduced both joint swelling and joint spirochete burdens compared with those in control mAb-treated mice. These studies indicate opposing roles for IL-4 and IFN-gamma in the modulation of spirochete growth and disease development in B. burgdorferi-infected mice and suggest that differential cytokine production early in infection may contribute to strain-related differences in susceptibility.

Role of IL-4 and IFN-gamma in modulation of immunity to Borrelia burgdorferi in mice

Because T cells appear to modulate the severity of murine Borrelia burgdorferi infections, we decided to examine the possible involvement of T cell-associated cytokines in disease outcome. Comparison of in vitro B. burgdorferi Ag-induced cytokine production in disease-susceptible and -resistant strains revealed striking differences; spleen cells from susceptible C3H mice produced significantly higher levels of IL-2 and IFN-gamma and lower levels of IL-4 than spleen cells from resistant BALB/c mice. Lymph node responses were even more divergent, with C3H mice producing high levels of IFN-gamma, and BALB/c mice producing little or none. This apparent Th1/Th2 cytokine imbalance was also reflected in vivo, since serum from C3H had significantly higher levels of B. burgdorferi-specific IgG2a Ab and lower levels of IgG1 Ab than serum from BALB/c mice. In vivo studies confirmed the importance of IL-4 in early control of spirochete growth, since treatment of either strain with neutralizing anti-IL-4 mAb led to increased joint swelling and higher spirochete burdens in joints compared with those in control mAb-treated mice. In contrast, IFN-gamma may hinder early control of spirochete growth in susceptible C3H mice, since treatment of mice with neutralizing anti-IFN-gamma mAb reduced both joint swelling and joint spirochete burdens compared with those in control mAb-treated mice. These studies indicate opposing roles for IL-4 and IFN-gamma in the modulation of spirochete growth and disease development in B. burgdorferi-infected mice and suggest that differential cytokine production early in infection may contribute to strain-related differences in susceptibility.

T cell subset-dependent modulation of immunity to Borrelia burgdorferi in mice

The possible involvement of specific T cells in resolution of infections with Borrelia burgdorferi (Bb), the causative agent of human Lyme disease, has not been adequately studied. To investigate the potential role of T cell subsets in resistance, we have depleted mice of CD4+ and CD8+ T cell subsets in vivo by the administration of specific mAbs and have examined outcomes after infection with Bb. Our results indicate that CD4+ T cells are required for immunologic control of spirochete levels, because their depletion in both susceptible C3H/HeN and resistant BALB/c mice increased the severity of arthritis and the numbers of spirochetes found in joints and skin, as compared with Bb-infected mice treated with a control mAb. In contrast, the CD8+ T cell compartment, particularly in susceptible C3H/HeN mice, appears to promote the disease process, possibly by interfering with the generation of protective immunity, as abrogation of this subset in vivo led to a reduction in both arthritis and in spirochete levels found in joints and skin when compared with Bb-infected control mice. Our inability to establish a correlation between resistance and Bb-specific IgG Ab levels in these mice raises the possibility that Ab-independent mechanisms are important in protection. These findings suggest that the final outcome in Bb-infected hosts may be the net effect of antagonistic influences exerted by CD4+ and CD8+ T cell subsets.

T cell subset-dependent modulation of immunity to Borrelia burgdorferi in mice

The possible involvement of specific T cells in resolution of infections with Borrelia burgdorferi (Bb), the causative agent of human Lyme disease, has not been adequately studied. To investigate the potential role of T cell subsets in resistance, we have depleted mice of CD4+ and CD8+ T cell subsets in vivo by the administration of specific mAbs and have examined outcomes after infection with Bb. Our results indicate that CD4+ T cells are required for immunologic control of spirochete levels, because their depletion in both susceptible C3H/HeN and resistant BALB/c mice increased the severity of arthritis and the numbers of spirochetes found in joints and skin, as compared with Bb-infected mice treated with a control mAb. In contrast, the CD8+ T cell compartment, particularly in susceptible C3H/HeN mice, appears to promote the disease process, possibly by interfering with the generation of protective immunity, as abrogation of this subset in vivo led to a reduction in both arthritis and in spirochete levels found in joints and skin when compared with Bb-infected control mice. Our inability to establish a correlation between resistance and Bb-specific IgG Ab levels in these mice raises the possibility that Ab-independent mechanisms are important in protection. These findings suggest that the final outcome in Bb-infected hosts may be the net effect of antagonistic influences exerted by CD4+ and CD8+ T cell subsets.

Further characterization of protective Trypanosoma cruzi-specific CD4+ T-cell clones: T helper type 1-like phenotype and reactivity with shed trypomastigote antigens

We previously reported the isolation from immune mice of a panel of murine clonal T-cell lines which specifically recognize antigens expressed by the trypomastigote stage of the protozoan parasite Trypanosoma cruzi, the causative agent of human Chagas' disease. Our analysis indicated that distinct clones which recognize common as well as strain-specific antigenic determinants were represented. The immunoprotective potential of several of these T-cell clones was demonstrated by adoptive transfer of protection to naive syngeneic recipients. Here we report that these T-cell clones are all of the TH1 phenotype, as determined from their lymphokine secretion patterns. Significant levels of stimulatory activity for each clone were detected in trypomastigote supernatants, and the release of this activity was time and temperature dependent. Seven of 10 T-cell clones tested responded to nitrocellulose-immunoblotted trypomastigote proteins in the range of 90 to 47 kDa; no fewer than six distinct epitopes residing on at least five distinct polypeptide species were recognized by this panel of clones. Two clones (2G8 and 4B10) previously shown to protect in vivo responded to immunoblotted proteins in the range of 65 to 53 and 90 to 80 kD, respectively. Stimulatory activity for the latter clone was shown to be expressed on the surface of trypomastigotes and to bind specifically to wheat germ agglutinin, indicating that its target antigen is an 85-kDa trypomastigote surface glycoprotein.

Isolation from Trypanosoma cruzi-infected mice of CD8+, MHC-restricted cytotoxic T cells that lyse parasite-infected target cells

Recent in vivo depletion studies in mice demonstrated that CD8+ T cells play a critical role in acute resistance to experimental Trypanosoma cruzi infections. As part of efforts to characterize these protective CD8+ T cell effector populations, we report here that splenic lymphocytes from mice chronically infected with T. cruzi can be induced to express high levels of cytolytic activity after stimulation in vitro with irradiated T. cruzi-infected macrophages. Cytolytic activity can either be detected using a nonspecific lectin-dependent 51Cr-release assay or using 51Cr-labeled T. cruzi-infected target cells. Fresh splenocytes from chronically infected mice stimulated with T. cruzi-infected macrophages exhibit relatively "promiscuous" killing activity inasmuch as significant lysis of both T. cruzi-infected and uninfected syngeneic and allogeneic cells is detected. However, subsequent rounds of in vitro stimulation lead to the expression of lytic activity that is T. cruzi Ag-specific and MHC-restricted. Several short term in vitro maintained cytolytic T cell lines were shown to have mixed phenotypes by FACS analysis; approximately 50% to 75% of the cells in these populations were CD4-, CD8+, whereas 20% to 40% were CD4-, CD8-. Experiments in which effector cells were positively selected by adherence to anti-CD8 mAb-treated plates confirmed that CD8+ T cell could exhibit Ag-specific cytolytic activity against T. cruzi-infected target cells. Efforts are under way to clone these CTL to test their in vivo function and to determine their Ag specificity.

Isolation from Trypanosoma cruzi-infected mice of CD8+, MHC-restricted cytotoxic T cells that lyse parasite-infected target cells

Recent in vivo depletion studies in mice demonstrated that CD8+ T cells play a critical role in acute resistance to experimental Trypanosoma cruzi infections. As part of efforts to characterize these protective CD8+ T cell effector populations, we report here that splenic lymphocytes from mice chronically infected with T. cruzi can be induced to express high levels of cytolytic activity after stimulation in vitro with irradiated T. cruzi-infected macrophages. Cytolytic activity can either be detected using a nonspecific lectin-dependent 51Cr-release assay or using 51Cr-labeled T. cruzi-infected target cells. Fresh splenocytes from chronically infected mice stimulated with T. cruzi-infected macrophages exhibit relatively "promiscuous" killing activity inasmuch as significant lysis of both T. cruzi-infected and uninfected syngeneic and allogeneic cells is detected. However, subsequent rounds of in vitro stimulation lead to the expression of lytic activity that is T. cruzi Ag-specific and MHC-restricted. Several short term in vitro maintained cytolytic T cell lines were shown to have mixed phenotypes by FACS analysis; approximately 50% to 75% of the cells in these populations were CD4-, CD8+, whereas 20% to 40% were CD4-, CD8-. Experiments in which effector cells were positively selected by adherence to anti-CD8 mAb-treated plates confirmed that CD8+ T cell could exhibit Ag-specific cytolytic activity against T. cruzi-infected target cells. Efforts are under way to clone these CTL to test their in vivo function and to determine their Ag specificity.

Stage-selective inhibition of rodent malaria by cyclosporine

The relative susceptibility of different developmental stages of Plasmodium berghei to cyclosporine was investigated in vivo. Within 12 h of receiving a single 25-mg/kg (body weight) dose of cyclosporine, mice with patent P. berghei infections uniformly exhibited a rapid fall in asexual parasite stages. Initially, ring forms and mature schizonts disappeared. Subsequently, trophozoites disappeared between 21 and 24 h, whereas gametocytes persisted for 36 h. In contrast, when cyclosporine was administered to mice 1 day before inoculation (100 mg/kg) with P. berghei sporozoites and for 2 consecutive days after inoculation (25 mg/kg), infections developed normally. When mice with patent infections were placed on prolonged cyclosporine therapy (25 mg/kg per day), parasitemia initially disappeared but often recrudesced. Recrudescent parasites were frequently resistant to cyclosporine (Csr). The Csr phenotype remained stable after serial passage of parasites in mice and after transmission through Anopheles stephensi mosquitoes, in which the capacity to produce oocysts was reduced. When infections of untreated mice were initiated with equal numbers of Csr and cyclosporine-susceptible (Css) parasites and then carried through two serial cycles of mosquito-to-mouse transmission without cyclosporine treatment, the Csr phenotype was lost. The results indicate that cyclosporine selectively inhibits asexual blood stages of P. berghei and favors the emergence of Csr parasites with diminished infectivity for mosquitoes.

Depression of virus-specific cytotoxic T-cell responses during murine malaria

Mice with self-limiting P. yoelii or fatal P. berghei infections exhibited a markedly impaired ability to mount specific splenic cytotoxic T-lymphocyte responses to immunization with infectious ectromelia (EV), vaccinia (VAC), or lymphocytic choriomeningitis viruses (LCMV). Lymph node responsiveness, however, was not impaired. Primary CTL responses were depressed in mice immunized 7 days after P. berghei infection, while in P. yoelii-infected mice, depressed responses were detected only during the period corresponding with maximal parasitemia (days 9-12). Secondary VAC-specific CTL responses in vitro by spleen cells of mice previously immunized during P. yoelii infection were also depressed if UV-inactivated rather than infectious VAC was used for immunization. In addition, spleen cells of mice already immune to VAC failed to yield normal secondary CTL responses in vitro during the period of maximal P. yoelii parasitaemia. Collectively, these findings indicate that, during patent malaria infections, priming for and expression of virus-specific CTL responses may be inhibited.

Isolation and functional characterization of murine T cell lines and clones specific for the protozoan parasite Trypanosoma cruzi

Murine T cell lines responsive to the protozoan parasite Trypanosoma cruzi were generated in vitro by stimulating hyperimmune C57BL/6 lymphoid cells with trypomastigote stage antigen. A spleen-derived line designated ST1 and eight clones derived from ST1 were characterized. All lines bear the surface phenotype Thy-1.2+, Ly-1.2+, 2.2- and respond to T. cruzi antigen only in the presence of antigen-presenting cells matched at the I-A subregion of the H2 locus. Clonal specificity analyses indicated that these T. cruzi-selected T cells are species specific and recognize antigenic determinants that are expressed predominantly in the trypomastigote stage. On the basis of their distinct patterns of response to a panel of different T. cruzi strains, clones recognizing strain-specific, shared, or common determinants were identified. Functional studies indicated that ST1 and some but not all of the clones are capable of expressing antigen-specific T helper function in vitro and in vivo. In addition, co-incubation of T. cruzi-specific T cells with cultured T. cruzi-infected syngeneic macrophages led to the dose-dependent destruction of intracellular parasites. Most notably, ST1 and several of the cloned T. cruzi-specific T cell lines were able to passively protect syngeneic recipients from lethal T. cruzi challenge infection. Efforts to identify the parasite antigens recognized by these T cell lines, particularly the protective clones, are currently in progress.

Isolation and functional characterization of murine T cell lines and clones specific for the protozoan parasite Trypanosoma cruzi

Murine T cell lines responsive to the protozoan parasite Trypanosoma cruzi were generated in vitro by stimulating hyperimmune C57BL/6 lymphoid cells with trypomastigote stage antigen. A spleen-derived line designated ST1 and eight clones derived from ST1 were characterized. All lines bear the surface phenotype Thy-1.2+, Ly-1.2+, 2.2- and respond to T. cruzi antigen only in the presence of antigen-presenting cells matched at the I-A subregion of the H2 locus. Clonal specificity analyses indicated that these T. cruzi-selected T cells are species specific and recognize antigenic determinants that are expressed predominantly in the trypomastigote stage. On the basis of their distinct patterns of response to a panel of different T. cruzi strains, clones recognizing strain-specific, shared, or common determinants were identified. Functional studies indicated that ST1 and some but not all of the clones are capable of expressing antigen-specific T helper function in vitro and in vivo. In addition, co-incubation of T. cruzi-specific T cells with cultured T. cruzi-infected syngeneic macrophages led to the dose-dependent destruction of intracellular parasites. Most notably, ST1 and several of the cloned T. cruzi-specific T cell lines were able to passively protect syngeneic recipients from lethal T. cruzi challenge infection. Efforts to identify the parasite antigens recognized by these T cell lines, particularly the protective clones, are currently in progress.

Susceptibility to acute Trypanosoma cruzi infection in autoimmune strains of mice

We previously observed that mice bearing the autoimmune associated lpr gene exhibit increased susceptibility to challenge with Trypanosoma cruzi, the causative agent of Chagas' disease. We have now tested two other autoimmune prone strains of mice, BXSB and NZB, and found that these animals also show increased sensitivity to acute T. cruzi infection. When challenged with a standard dose (10(2)) of Y strain trypomastigotes, BXSB males (BXSB-YSB), which develop early onset autoimmune disease, suffered high mortality, while late onset autoimmune BXSB females and minimally autoimmune male BXSB mice whose Y chromosome was derived from C57BL/6J mice (BXSB-YB/6) also recover. NZB mice were found to be highly susceptible to challenge while NZW and NZB/W were resistant. A finding common to all groups of susceptible autoimmune mice was increased plasma levels of T. cruzi specific antibody, especially IgM. The data indicate that in two of the three autoimmune prone strains examined, increased T. cruzi susceptibility appears to be linked to restricted genetic elements (i.e. lpr gene and the YSB associated factor) which also influence the rapidity of onset of autoimmunity.

Inhibition by cyclosporin A of rodent malaria in vivo and human malaria in vitro

The development and course of normally lethal parasitemias in mice inoculated intraperitoneally with erythrocytic stages of Plasmodium yoelii or Plasmodium berghei were markedly affected by treatment with the antilymphoid drug cyclosporin A (CS-A). When the first of four daily subcutaneous 25-mg/kg doses of CS-A was given at the time of parasite inoculation, patent infections failed to develop. If begun up to 5 days earlier, this same treatment regimen prolonged the prepatent period, attenuated parasitemia, and reduced mortality. In mice with patient infections, two consecutive daily 25-mg/kg doses of CS-A were sufficient to terminate parasitemias which, after several days, reappeared but were self-limiting. This pattern of apparent cure followed by transient recrudescence remained unaltered even when daily treatment with the same drug dose was continued for 3 weeks. Recrudescence was associated with the emergence of parasite populations that were relatively resistant to CS-A and, in the case of P. yoelii, of reduced virulence. In more limited experiments, CS-A was found to be active in vitro against erythrocytic stages of the human malarial parasite palsmodium falciparum. Depending on the concentration of drug in the culture medium, parasite growth was either prevented or inhibited.