André Capron

Cell dysfunction and depletion in AIDS: the programmed cell death hypothesis

Normal immature thymocytes respond to activation by undergoing programmed cell death (apoptosis), a physiological deletion mechanism involved in the selection of the T-cell repertoire. In this article, Jean Claude Ameisen and André Capron suggest that inappropriate induction of a form of programmed T-cell death could account for both qualitative and quantitative helper T-cell defects of HIV-infected patients. A model of AIDS pathogenesis is presented that may explain several features of HIV infection, including evolution of the disease and the development of defects in nonimmunological organs.

Release of prostaglandin D2 into human airways during acute antigen challenge

Among the many possible mediators of the early asthmatic response, prostaglandin D2, a bronchoconstrictor, is the principal cyclooxygenase metabolite of arachidonic acid that is released upon the activation of mast cells and is also synthesized by human alveolar macrophages. We performed bronchoalveolar lavage in five patients with chronic stable asthma, before and up to nine minutes after local provocative challenge with Dermatophagoides pteronyssinus. The lavage fluid was analyzed for products of arachidonic acid metabolism. Prostaglandin D2 levels in all five patients rose an average of 150-fold, from less than 8 to 332 +/- 114 pg per milliliter (mean +/- SEM; P less than 0.050), after local instillation of the antigen. Levels of 15-hydroxyeicosatetraenoic acid, which may also have a role in the pulmonary allergic response, were detectable in lavage fluid before challenge and increased after provocation with the antigen in four of the five patients. The activity of beta-glucuronidase, an enzyme released by macrophages and mast cells upon stimulation, tended to increase in the lavage fluid after provocation in all patients. These studies provide evidence that the release of prostaglandin D2 into the airways is an early event after the instillation of D. pteronyssinus in patients who are sensitive to this antigen.

Increased secretion of tumor necrosis factor α and interleukin-6 by alveolar macrophages consecutive to the development of the late asthmatic reaction

The late asthmatic reaction (LAR), consecutive to bronchial allergen challenge, is characterized both by the influx of various cells in proximal and distal airways and by the enhancement of bronchial hyperresponsiveness. However, the exact conditions for the development of the inflammatory reaction during the LAR remain to be specified. Since monokines play a key role in inflammatory processes, particularly in the lung, the production of tumor necrosis factor-alpha (TNF-alpha), interleukin; 1-beta (IL-1-beta) and interleukin-6 (IL-6) by alveolar macrophages (AM), collected 18 to 20 hours after exposure to allergen, was evaluated in 15 allergic subjects with asthma submitted to a challenge test with Dermatophagoides pteronyssinus (N = 6) or with wheat flour (N = 9) and in three healthy subjects. After bronchial provocation test, four patients presented no bronchial response (group 1), and six patients, a single early reaction (group 2). In contrast, five patients developed successively an immediate plus a late response (group 3). The monokine production was compared to that from nine allergic subjects with asthma studied at baseline (group 0) and from 11 unchallenged healthy subjects (control subjects). Measurements of cytokines were evaluated for TNF-alpha and IL-1-beta by a specific immunoradiometric assay, whereas IL-6 levels were appreciated by the proliferation of 7TD1 cells. No detectable amounts of TNF-alpha, IL-1-beta, and IL-6 were in bronchial alveolar lavage fluid, even after a tenfold concentration. In contrast, a significant increase of TNF-alpha (10,642 +/- 3127 U/ml) and IL-6 (1250 +/- 427 U/ml) concentrations was noted in AM supernatants from patients exhibiting an LAR (group 3) compared to cells recovered from groups 2, 1, and 0 and to challenged or unchallenged control subjects (805 +/- 244, 995 +/- 521, 1269 +/- 524, 688 +/- 85, and 445 +/- 74 pg of TNF-alpha per milliliter, respectively; 190 +/- 64, 114 +/- 91, 242 +/- 95, 80 +/- 9, and 54 +/- 19 U/ml of IL-6 per milliliter, respectively). No modification of IL-1-beta contents could be detected between the different groups. A significant correlation was detected between concentrations of TNF and IL-6 (r = 0.92; p less than 0.001). These results demonstrate TNF-alpha and IL-6 secretion by AM consecutively to the development of LAR in allergic subjects with asthma, confirming that AMs are activated after allergen challenge.(ABSTRACT TRUNCATED AT 400 WORDS)

Involvement of immunoglobulin E in the secretory processes of alveolar macrophages from asthmatic patients.

Alveolar macrophages from nonatopic donors were passively sensitized with allergen-specific IgE antibody from the serum of asthmatic patients. A selective release of 4-8% of the lysosomal beta-glucuronidase of these cells occurred within 30 min of contact with the related allergen or with anti-human IgE antibody, in the absence of any mast or basophil cells. The cell reactivity was dependent on the interaction of macrophages with IgE, as shown by the disappearance of the allergen-induced enzyme release after heating or IgE-immune adsorption of the sensitizing serum, but not after IgG-adsorption. Alveolar macrophages from asthmatic patients behaved similarly to passively sensitized normal macrophages. Contact with the related allergen or with anti-IgE antibody induced the same percentage of enzyme release, demonstrating that these cells possess allergen-specific IgE bound on their surface. 18% of them formed rosettes with anti-IgE-coated sheep erythrocytes, and 15-22% with allergen-coated erythrocytes, but lost this property after preincubation with the specific allergen. The presence of IgE-specific receptors on the macrophage surface was demonstrated both at the ultrastructural level with immunoperoxidase labeling, and at low magnification by the formation of 15-18% rosettes with human IgE-coated erythrocytes. The formation of such rosettes was inhibited after incubation of alveolar phagocytes with aggregated myeloma IgE. On the basis of these observations, the participation of the alveolar macrophages in IgE-mediated pulmonary hypersensitivity must be considered. Its precise involvement requires, however, further investigations.

Molecular cloning of a protective antigen of schistosomes.

The complementary DNA sequence encoding the Mr 28,000 antigen of Schistosoma mansoni has been isolated and expressed in Escherichia coli. Experimental vaccination of rats, hamsters and monkeys with a recombinant fusion protein induces a strongly cytotoxic antibody response. Immunization of rats and hamsters with this protein leads to significant protection against a natural challenge infection with live cercariae.

From parasites to allergy: a second receptor for IgE

Human allergic responses are triggered when mast cells bind IgE antibodies. IgE production is also a regular feature of helminth infection and parasites can be killed by inflammatory cells such as macrophages, eosinophils and platelets sensitized by reaginic antibody. The IgE receptor they use has been identified only recently. Here André Capron and his colleagues discuss how it differs from the IgE receptor present on mast cells.

Immunization of mice and baboons with the recombinant Sm28GST affects both worm viability and fecundity after experimental infection with Schistosoma mansoni

Summary A member of the glutathione S‐transferase family. Sm28GST has previous! demonstrated a good ability to protect rodents against experimental infection with Schistosoma mansoni. In order lo evaluate its efficacy in a model closer to man, two different protocols of immunization with recombinant Sm28GST were tested on baboons in a large‐scale trial. Three injections in the presence of aluminium hydroxide as adjuvant resulted in a significant 38% reduction in the adult worm burden together with a trend for a lower percentage of inflammatory tissue in the liver. Individual levels of protection, ranging from 0 to 80%, underlined the heterogeneity of the immune response to this purified molecule in outbred primates. On the other hand, two injections of Sm28GST in the presence of aluminium hydroxide and Bordetella pertussis reduced female schistosome fecundity by 33%, with a more pronounced effect (66%) on faecal egg output; there was also a trend, in this protocol, for decrease of the mean granuloma surface in the liver. Individual anti‐Sm28GST IgG antibodies were apparently unrelated to levels of immunity, but there was partial evidence that cytophilic IgE might play a role in the immune mechanisms affecting worm viability, but not fecundity. In the mouse model, Sm28GST vaccination resulted in a lower hatching ability of tissue eggs recovered from immunized mice whereas passive transfer of specific anti‐Sm28GST T‐lymphocytes, one day before infection, significantly reduced the number of eggs in the liver of mice. We propose that different protocols of immunization with a recombinant molecule can impede Schistosoma mansoni worm viability and fecundity, but can also affect miracidium

STIMULATION OF ALVEOLAR MACROPHAGES IN ASTHMATIC PATIENTS AFTER LOCAL PROVOCATION TEST

Dermatophagoîdes pteronyssinus allergen was instilled into the alveolar space of 7 allergic asthmatic patients during bronchoalveolar lavage. beta-glucuronidase concentration in the bronchoalveolar fluid from the challenged lung became significantly higher than that in the opposite control lung (3.90 +/- 1.88 nmol/h versus 0.86 +/- 0.55). The intracellular level of beta-glucuronidase in the alveolar macrophages in the challenged lung was 40.3% lower than that in the control lung. In 3 controls intracellular concentrations of beta-glucuronidase were similar before and after allergenic challenge and no enzyme activity could be detected in bronchoalveolar lavage fluid. These results suggest that alveolar instillation of an allergen in asthmatic patients rapidly stimulates alveolar macrophages, which may be involved in immediate hypersensitivity reactions in asthma.

Toxoplasma gondii: Characterization and localization of antigens secreted from tachyzoites

Since we had previously demonstrated the protective role played by Toxoplasma excreted-secreted antigens, the aim of the present work was to produce monoclonal antibodies directed against these antigens in order to determine if their localization in the parasite is compatible with a mechanism of excretion or secretion. Western immunoblotting analysis revealed three monoclonal antibodies (TG17-179, TG17-43, and TG17-113) raised against excreted-secreted antigens of 28.5, 27, and 21 kDa, respectively. The TG17-179 which reacts with antigens isolated by Concanavalin A affinity chromatography is directed against a glycosylated 28.5-kDa component. Colloidal immunogold labeling showed the ultrastructural localization of the 21-, 27-, and 28.5-kDa antigens in the matrix of the dense granules of tachyzoites and associated with the microvilli network of the parasitophorous vacuole, after host cell invasion. These observations suggest the following mechanism of Toxoplasma secretion: secreted antigens are first stored in tachyzoite-dense granules and are then released inside the parasitophorous vacuole. Among the secretory molecules characterized here, the native 27-kDa antigen recognized by TG17-43 is a calcium-binding protein found to be intermixed with the 21- and 28.5-kDa antigens inside the dense granules and hence could play a role in the packaging of secretory products. In addition, the 21- and 28.5-kDa antigens were also located beneath the parasite plasma-lemma. This particular location could reflect a transient step characteristic of T. gondii secretion.

Proteolytic cleavage of IgG bound to the Fc receptor of Schistosoma mansoni schistosomula

After the binding of IgG to the surface Fc receptor of Schistosoma mansoni schistosomula, the Fab portions of IgG are cleaved and small peptides are liberated in the culture medium. At least two types of proteinase activities have been demonstrated in the secretory products of schistosomula. One is an endoprotease with trypsin‐like activity, with an optimum pH of 7 and an optimum temperature of 45°C. The other is a metalloaminopeptidase with an optimum pH of 7 and temperature of 37°C.