Regina A. Silva

Blocking the Receptor for IL-10 Improves Antimycobacterial Chemotherapy and Vaccination

Novel approaches are required for the prevention and therapy of mycobacterial infections since the only vaccine in use, bacillus Calmette-Guérin, is poorly effective and chemotherapy is long and often ineffective in sterilizing the infection. We used a mouse model of Mycobacterium avium infection to address the usefulness of a mAb able to block IL-10R both in treatment of primary infections and in conventional multidrug therapy and subunit vaccination. Treatment of infected mice with this mAb during the entire period of experimental infection had little impact on the course of M. avium infection, with a slight improvement in the resistance of infected mice observed in the liver and spleen at day 30 of infection, which was associated with increased macrophage activation and priming of CD4+ T cells for IFN-γ production. Administration of this mAb later in infection had no effect on its course, but improved the effectiveness of chemotherapy when the latter was started in a chronic phase of infection. Also, the anti-IL-10R mAb acted as an adjuvant in the induction of protective immunity upon vaccination with a mycobacterial subunit preparation.

Analysis of T cells recruited during delayed‐type hypersensitivity to purified protein derivative (PPD) versus challenge with tuberculosis infection

The delayed‐type hypersensitivity (DTH) to purified protein derivative (PPD) test has been used to infer about protective immunity to Mycobacterium tuberculosis and to diagnose tuberculosis. We showed that in memory tuberculosis‐immune mice both DTH to PPD and resistance to M. tuberculosis could be effectively elicited in the footpad and both reactions led to the accumulation of reactive T cells in the regional lymph nodes with a CD4+ phenotype and characterized by the secretion of high levels of interleukin‐2 (IL‐2) and interferon‐γ (IFN‐γ) and no IL‐4. By adoptive transfer into nude mice of highly purified CD4+ T cells harvested during the recall of protective immunity it was confirmed that this population mediated both manifestations. However, the specificity of the T cells recruited during these processes were found to differ markedly; T cells involved in protection to a challenge with live tuberculosis bacilli recognized predominantly low‐mass culture filtrate antigens below 15 000 MW, while cells recruited during DTH to PPD were directed to molecular mass fractions between 15 000 and 31 000. Using single purified antigens we showed that the latter cells recognized the secreted mycobacterial protein Ag85B and the heat‐shock proteins, DnaK and GroEL. Protective T cells, in contrast, were characterized by a very high frequency of T cells directed to the ESAT‐6 peptide 1–20.

Interleukin 12 primes CD4+ T cells for interferon-γ production and protective immunity during Mycobacterium avium infection

Interleukin‐12 (IL‐12) is a crucial cytokine for the generation of a protective immune response against Mycobacterium avium infection. In contrast to infected control mice, IL‐12‐deficient mice were unable to control bacterial proliferation and their spleen T cells were almost unresponsive in vitro to specific antigens of M. avium. Susceptibility of mice deficient in IL‐12 was similar to that of interferon‐γ (IFN‐γ)‐deficient mice. These data indicate a crucial role of IL‐12 in the development of a T‐cell population able to produce IFN‐γ and to mediate protection against M. avium infection. Treatment of M. avium‐infected mice with IL‐12 induced CD4+ T cells with enhanced capacity to produce IFN‐γ as well as to confer increased protection against M. avium.

Blocking the receptor for interleukin 10 protects mice from lethal listeriosis

ABSTRACT High doses of Listeria monocytogenes overcome the ability of a normal mouse to control the infection, due to massive bacterial replication. Treatment with an anti-interleukin 10 (IL-10) receptor monoclonal antibody prevented the fatal course of infection with high doses of bacteria. This work shows that blocking the receptor for IL-10 may have useful therapeutic applications.

Effects of Interleukin‐12 in the Long‐term Protection Conferred by a Mycobacterium avium Subunit Vaccine

The effects of the addition of recombinant interleukin (IL)‐12 to a mycobacterial subunit vaccine were analyzed in terms of the longevity of the protective immunity generated. BALB/c mice were immunized with culture filtrate proteins from Mycobacterium avium with dimethyl‐dioctadecilammonium bromide (DDA) as an adjuvant. This subunit vaccine induced protection against a challenge by M. avium which lasted for at least 6 months while waning with time until 1 year postvaccination. Whereas the addition of IL‐12 enhanced the initial protective efficacy of this subunit vaccine during the first 6 months, it accelerated the loss of protective efficacy observed at 1 year postvaccination. These data confirm the adjuvant properties of IL‐12 in vaccines against mycobacteria and raise the possibility of late counter‐protective untoward effects.

Minor role played by type I tumour necrosis factor receptor in the control of Mycobacterium avium proliferation in infected mice

Control of mycobacterial growth depends on the concerted activity of different cytokines acting in different stages of the development of innate and adaptive immune responses. Tumour necrosis factor‐α (TNF‐α) has been shown to play a protective role in Mycobacterium avium infections. Here we assessed the growth of this mycobacterial species in wild‐type mice and in mice with a genetically engineered disruption of the type I receptor for TNF‐α (p55‐KO mice). p55‐KO mice infected with a low‐virulence strain of M. avium exhibited a slightly delayed capacity to eliminate the micro‐organisms from the liver as compared with wild‐type animals. However, either the growth of this strain in the other organs studied (spleen and lung) or the growth of two other strains of M. avium with intermediate or high virulence, failed to be affected by mutation of the TNF‐α receptor. p55‐KO mice were also as protected by the administration of recombinant interleukin‐12 as the heterozygous p55 +/– mice. We conclude that signalling through the type I TNF receptor plays a small role in vivo in the induction of mycobacteriostasis during M. avium infection but may improve survival during infection with virulent mycobacteria, independently of the extent of their proliferation.

Cytokines Involved in Resistance to Mycobacterium avium in a Mouse Model of Infection

To determine the role played by different cytokines in the induction or expression of protective immunity to Mycobacterium avium we administered neutralizing monoclonal antibodies specific for those cytokines to mice infected with a clinical isolate of M. avium. Our results showed that interleukin (IL)-6 and IL-12 are involved in the induction of T cell-dependent immunity and that such immunity was mediated by interferon-γ (IFN-γ) and tumour necrosis factor-α (TNF-α). Also, induction of innate immunity required IL-12 and was expressed through the secretion of IFN-γ and TNF-α.