Biomedical subjects

Célio L Silva

Publications and source records attributed to Célio L Silva.

5 recordsLinked to original sources

PubMed2005

Efficacy of cell-free antigens in evaluating cell immunity and inducing protection in a murine model of histoplasmosis.

Histoplasma capsulatum is a dimorphic pathogenic fungus that causes a wide spectrum of disease when mycelial fragments are inhaled. Resistance to H. capsulatum is dependent on cellular immunity mediated by T cells and macrophages. Here we standardized the production of extracts containing cell-free antigens (CFAgs) and observed their efficacy in evaluating cellular immunity during murine histoplasmosis. CFAgs induced a more potent delayed-type hypersensitivity (DTH) response in H. capsulatum-infected mice than did histoplasmin-a classical antigen. This DTH response to CFAgs is able to determine the immune status of infected mice and to predict their death. Moreover, CFAgs stimulated spleen cells from immune mice to produce higher amounts of gamma interferon (IFN-gamma) in vitro. Finally, immunization with CFAgs protected against a lethal inoculum of H. capsulatum. These results demonstrate that CFAgs may be useful for the evaluation of cellular immune response and as a potential source for the development of a vaccine against histoplasmosis.

Animals↗

PubMed2005

Immunomodulation and protection induced by DNA-hsp65 vaccination in an animal model of arthritis.

We described a prophylactic and therapeutic effect of a DNA vaccine encoding the Mycobacterium leprae 65-kDa heat shock protein (DNA-hsp65) in experimental murine tuberculosis. However, high homology of the vaccine to the corresponding mammalian hsp60, together with the CpG motifs in the plasmidial vector, could trigger or exacerbate an autoimmune disease. In the present study, we evaluate the potential of DNA-hsp65 vaccination to induce or modulate arthritis in mice genetically selected for acute inflammatory reaction (AIR), either maximal (AIRmax) or minimal (AIRmin). Mice immunized with DNA-hsp65 or injected with the corresponding DNA vector (DNAv) developed no arthritis, whereas pristane injection resulted in arthritis in 62% of AIRmax mice and 7.3% of AIRmin mice. Administered after pristane, DNA-hsp65 downregulated arthritis induction in AIRmax animals. Levels of interleukin (IL)-12 were significantly lower in mice receiving pristane plus DNA-hsp65 or DNAv than in mice receiving pristane alone. However, when mice previously injected with pristane were inoculated with DNA-hsp65 or DNAv, the protective effect was significantly correlated with lower IL-6 and IL-12 levels and higher IL-10 levels. Our results strongly suggest that DNA-hsp65 has no arthritogenic potential and is actually protective against experimentally induced arthritis in mice.

Animals↗

PubMed2004

Vaccine adjuvant: it makes the difference.

The use of protein or DNA in vaccination process rather than living or attenuated microorganism, aims at the increase of the vaccines safety. However, in these cases, the use of adjuvant is frequently required to improve their immunogenicity. In this study, we show the importance of the adjuvant in a vaccine formulation. Vaccines for tuberculosis provide an instructive example, based on the mycobacterial 65 kDa heat shock protein (hsp65). The same antigen can elicit completely different patterns of immune response depending on how it is administered. Thus, the same antigen might or not protect mice from challenge with Mycobacterium tuberculosis, depending on the formulation. These data suggest that, despite the name, the adjuvant plays a fundamental role on the vaccination process.

Adjuvants, Immunologic↗

PubMed2004

Blockade of endogenous leukotrienes exacerbates pulmonary histoplasmosis.

Leukotrienes are classical mediators of inflammatory response. New aspects of leukotriene function have recently been described. We examine here the previously unreported role that leukotrienes play in the regulation of cytokines in a murine model of histoplasmosis. We demonstrate that administration of MK 886, a leukotriene synthesis inhibitor, caused Histoplasma capsulatum-infected mice to die by the day 15 of infection, whereas the correlating death rate in untreated infected mice was 0%. Treating infected animals with MK 886 inhibited leukotriene synthesis but increased leukocyte recruitment to the lungs. Subsequent to this phenomenon, levels of tumor necrosis factor alpha, interleukin-1 (IL-1), IL-6, and KC chemoattractant cytokines and fungi in the lung parenchyma increased, as did inflammatory response. In contrast, IL-2, IL-5, IL-12, and gamma interferon cytokine levels actually decreased. Thus, murine response to pulmonary histoplasmosis may be leukotriene modulated. This finding may enable us to alter the course of the immune response and inflammation caused by histoplasmosis. The data from the present study suggest an important new strategy for immunologic or drug intervention in human patients.

Animals↗

PubMed2002

The Mycobacterium leprae hsp65 displays proteolytic activity. Mutagenesis studies indicate that the M. leprae hsp65 proteolytic activity is catalytically related to the HslVU protease.

The present study reports, for the first time, that the recombinant hsp65 from Mycobacterium leprae (chaperonin 2) displays a proteolytic activity toward oligopeptides. The M. leprae hsp65 proteolytic activity revealed a trypsin-like specificity toward quenched fluorescence peptides derived from dynorphins. When other peptide substrates were used (beta-endorphin, neurotensin, and angiotensin I), the predominant peptide bond cleavages also involved basic amino acids in P(1), although, to a minor extent, the hydrolysis involving hydrophobic and neutral amino acids (G and F) was also observed. The amino acid sequence alignment of the M. leprae hsp65 with Escherichia coli HslVU protease suggested two putative threonine catalytic groups, one in the N-domain (T(136), K(168), and Y(264)) and the other in the C-domain (T(375), K(409), and S(502)). Mutagenesis studies showed that the replacement of K(409) by A caused a complete loss of the proteolytic activity, whereas the mutation of K(168) to A resulted in a 25% loss. These results strongly suggest that the amino acid residues T(375), K(409), and S(502) at the C-domain form the catalytic group that carries out the main proteolytic activity of the M. leprae hsp65. The possible pathophysiological implications of the proteolytic activity of the M. leprae hsp65 are now under investigation in our laboratory.

ATP-Dependent Proteases↗