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A prospective study was undertaken to define early predictive immunological marker(s) of exposure to Leishmania in naïve subjects who have never been exposed to any Leishmania and who were also free of any cutaneous leishmaniasis lesions. These naïve subjects could have been exposed to Leishmania in a rain forest where Leishmania guyanensis and their natural vectors and mammalian host are cocirculating. The production of interferon (IFN)-gamma in response to the Leishmania homologue of the mammalian receptor for activated c kinase (LACK), a candidate for vaccine against leishmaniasis was analysed. At the end of their stay in the rain forest, LACK-specific CD8+ T cells were detected in subjects whose peripheral blood mononuclear cell (PBMC) produced IFN-gamma in response to soluble Leishmania antigens (SLA) and in those whose PBMC remained unresponsive to SLA. However, LACK-specific CD4+ T cells were detected only in PBMCs from individuals who became IFN-gamma responders to SLA. In subjects whose PBMC became positive to SLA, LACK-reactive CD4+ T cells producing high level of IFN-gamma were detectable before the SLA-reactive IFN-gamma producing CD4+ T cells, suggesting that the former readout assay could be used as an early predictive immunological marker of exposure to Leishmania in subjects who remained disease free.

We showed in a previous study that the intranasal (i.n) delivery of bacille Calmette-Guérin (BCG) to BP2 mice (H-2q) inhibits eosinophilia and bronchial hyperreactivity in a mouse model of asthma. The present work has been performed to characterize the leucocyte lineages recruited to the lungs of mice after i.n. delivery of BCG and potentially involved in the polarization of T lymphocytes. The different antigen-presenting cells (APC) recruited to bronchoalveolar lavage (BAL) and to lung tissue of mice shortly after the delivery of BCG were analysed in parallel as well as their capacity to drive the immune response towards a T helper type 1 cytokine production. Alveolar macrophages (AM) from the BAL were CD11c+, F4/80+ and CD11b-, and in the lung tissue two major populations of potential APC were detected: one CD11c-, F4/80+, CD11b+ and I-Aq- was identified as interstitial macrophages (IM) and a second expressing CD11c+ and I-Aq+ antigens, negative for CD11b and F4/80 markers as leucocytic dendritic cells (DC). Freshly isolated DC up-regulated CD11b and CD40 antigens after overnight culture, but remained negative for CD8alpha antigen, suggesting a myeloid origin. Lung DC which produced high amount of interleukin (IL)-12 were potent inducers of naive CD4+ T lymphocyte priming, as assessed by interferon-gamma (IFN-gamma) production by these naive CD4+ T cells. Lung explants recovered long term after BCG delivery produced sustained levels of IFN-gamma. Our results suggest that AM and particularly DC by secreting IL-12 shortly after BCG delivery induce the long-term persistence of IFN-gamma-secreting T cells percolating in BCG-loaded lung tissue.

Cell-mediated immunity plays a key role in containing the growth of Mycobacterium tuberculosis in the host. The induction of an antibody response or a mixed cell-mediated and humoral response is frequently associated with tuberculosis disease or a decrease in the ability to control M. tuberculosis load. We recently reported the induction of similar immune responses and protection by rectal, subcutaneous (SC) or intradermal administration of Mycobacterium bovis BCG in adult mice, guinea pigs and macaques. The rectal immunization, which did not induce the side-effects associated with parenteral routes (axillary adenitis) and which could be used to reduce the risks of viral transmission associated with unsafe injections in the developing world, was analysed and compared in newborn and adult BALB/c mice. The rectal and SC immunization induced, in mice immunized as newborns or as adults, a mixed T helper 1/T helper 2 (Th1/Th2) immune response; however, particularly in adult mice, after SC administration of BCG, the level of Th2 immune response is significantly higher than it is by the rectal route. Six months after immunization with BCG, rectal and SC delivery induced similar levels of protective immunity against a virulent challenge with M. tuberculosis strain (H37Rv) in mice immunized as adults, but the rectal BCG delivery triggered stronger protection than the SC delivery if mice were immunized as newborns.

Mechanisms of constitutive and acquired susceptibility/resistance to Leishmania Viannia panamensis (L. (V ) p.) were investigated in endemically exposed human populations presenting either recurrent disease (putative susceptible) or subclinical infection (clinically resistant). Cutaneous delayed type hypersensitivity response to leishmanin was significantly lower among individuals experiencing recurrent leishmaniasis than among those whose skin test converted without developing the disease. Monocyte derived macrophages from individuals with recurrent disease were more permissive in vitro to the entry of parasites than macrophages from subclinically infected individuals. In vitro proliferation of CD4 and CD8 T lymphocytes in response to intracellular amastigotes was significantly lower among individuals with a history of recurrent disease compared with subclinically infected individuals. Linear regression analyses revealed a strong direct relationship between the production of interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-10 by peripheral blood mononuclear cells (PBMC) from resistant (subclinically infected) individuals and no correlation in the production of these cytokines by PBMC from individuals who experienced recurrent disease. The results provide evidence of differences in the innate and acquired responses to Leishmania according to the outcome of the natural infection. These findings support the feasibility of identifying the immunological bases of innate and acquired resistance through studies in naturally exposed human populations.

Galectin-3, also known as the macrophage marker Mac-2, is a member of a family of structurally related animal lectins that exhibit specificity for beta-galactosides. In order to investigate the role of galectin-3 in acute inflammation, we have compared the number of leucocytes present in the peritoneal cavity of wild type and galectin-3 null mutant mice after intraperitoneal (i.p.) injection of thioglycolate broth. At day 1 after injection, we found no difference in the recruitment of mononuclear phagocytes and granulocytes to the peritoneal cavity. However, 4 days after thioglycolate injection, galectin-3 mutant mice exhibited a significantly reduced number of recoverable granulocytes compared to wild-type animals. As mutant granulocytes did not exhibit an accelerated rate of apoptosis and their uptake by macrophages appeared to be unaffected by the mutation, the phenotype described here suggests that galectin-3 participates in an additional level of control during the resolution of acute inflammation.

Evidence for pleiotropic activation of virulence genes in Listeria monocytogenes is presented. A complementation study of a spontaneous prfA-deletion mutant and analysis of cassette and transposon insertion mutants showed that the gene prfA activates the transcription of four independent genes which code for a phosphatidyl-inositol-specific phospholipase C (gene plcA), listeriolysin O (gene hlyA), a metallo-protease (gene prtA) and a lecithinase (gene prtC). Transcription of prfA is not constitutive. During the growth phase, two peaks of prfA transcript accumulation were observed: the first was during exponential growth, and the second was at the beginning of the stationary phase. In addition, two prfA-specific transcripts of 2.2 kb and 1 kb are detected. Early in exponential growth, prfA is co-transcribed with plcA which lies upstream prfA, giving rise to the 2.2 kb plcA-prfA transcript. In late-exponential growth and at the beginning of the stationary phase, prfA transcripts of 1 kb are predominantly detected. Our results demonstrate that since prfA controls plcA transcription, it also regulates its own synthesis.

When mice were homozygous for the Wf allele at W locus, the delayed-type hypersensitivity (DTH) reaction observed in mice primed i.v. or s.c. with optimal doses of sheep red blood cells was greatly decreased. The number of sensitized splenic cells able to transfer a delayed-type hypersensitivity reaction was identical in +/+ and Wf/Wf primed mice. At site of local transfer of +/+ sensitized cells and antigen, the recruitment of monocytes was identical in +/+ and Wf/Wf mice. In contrast, the number of blood cells able to transfer a DTH reaction was decreased by a factor 40 in Wf/Wf primed mice compared to +/+ ones. This decreased number of sensitized cells in blood of Wf/Wf mice revealed a specific defective circulation of Wf/Wf DTH mediating cells whatever the genotypes (+/+ or Wf/Wf) of recipients used to measure this property of circulation.

The delayed-type hypersensitivity DTH) reaction observed in mice primed i.v. with low doses of sheep red blood cells was greatly decreased when mice were irradiated with 300 rad before priming. An estimation of the radiosensitivity of DTH-mediating cells (DTH-C) was performed using a titration assay after local adoptive transfer of these cells mixed with antigen into the footpad of unprimed mice. A high radiosensitivity of the induction of DTH-C was observed with a D37 of approximately 50 rad. In contrast, the expression of DTH-C appeared radioresistant, as the D37 was approximately 2000 rad.

The delayed-type-hypersensitivity (DTH) reaction observed in mice primed i.v. with low doses of sheep red blood cells is not detectable after priming with large doses. Estimation of the number of DTH mediating cells (DTH-C) was performed by titration (D50 determination) using local adoptive transfer of these cells mixed with antigen into footpads of unprimed mice. In opposition to the absence of peripheral DTH-C, splenic DTH-C were more numberous after large doses than after low doses of antigen. The ability of cyclophosphamide to restore DTH responsiveness in mice primed with large doses appeared to be related to an increased cirulation of DTH-C. These cell circulated only in mice without any detectable B-cell response or in which this response was depressed. Thus a B-cell dependent splenic retention process of DTH-C is discussed as the origin of DTH unresponsiveness observed after priming with large doses of antigen.

Sensitized lymphocytes transferred locally with antigens into footpads of unprinted mice can elicit a delayed-type-hypersensitivity (DTH) reaction. Treatment of recipients with cyclophosphamide (CY) increased the infiltration observed at the DTH site. The enlargement of footpads was detected with low doses of DTH mediating cells as with large ones. An enumeration of circulating monocytes performed on the test days and the preceding days has shown a three to ten fold increase of number of monocytes. During the recovery following CY treatment (20 mg/kg and 200 mg/kg) a rebound effect at level of precursors of monocytes was observed. Thus a dual mechanism is proposed to explain the effect of CY on DTH reaction: a liberation of DTH cells by inhibition of B response as previously described; an increased number of monocytes which can be recruited by DTH-cells in site of antigen injection.