Resident and monocyte-derived dendritic cells become dominant IL-12 producers under different conditions and signaling pathways.

IL-12 is such a pivotal cytokine that it has been called the third signal for T cell activation, TCR engagement being the first and costimulation being the second. It has been generally viewed that the resident CD8(+) dendritic cell (DC) subset is the predominant IL-12-producing cell type. In this study, we found, although this is so under steady state conditions, under inflammatory conditions monocyte-derived DC (mDC) became a major cell type producing IL-12. Depletion of either type of DC resulted in reduced production of IL-12 in vivo. For CD8(+) DC, IL-12 production could be stimulated by various pathways viz. signaling through MyD88, Trif, or nucleotide-binding oligomerization domain (Nod)-like receptors. In contrast, for mDC, IL-12 production was mainly dependent on MyD88 signaling. Thus, conventional DCs and mDCs use different pathways to regulate IL-12 production.

Synergism between active listeriolysin O and dimethyldioctadecylammonium bromide to activate CD8(+) T cells.

Purified recombinant listeriolysin O (LLO) was assessed for its ability to induce T cell responses in mice. Intraperitoneal immunisation with LLO, as a fusion with glutathione-S-transferase (GST), induced the production of LLO-specific CD8(+) T cells, but not LLO-specific CD4(+) T cells. The generation of this response could be blocked by pre-treatment with cholesterol, indicating a requirement for LLO pore formation. An increase in the LLO-specific response of both CD8(+) and CD4(+) T cells could be detected following the addition of dimethyldioctadecylammonium bromide (DDA), although the generation of this response was not dependent upon LLO pore formation, suggesting that DDA might change the presentation pathway of LLO leading to activation of the CD8(+) T cells. However, this response was dependent upon the presence of structurally intact LLO, suggesting a requirement for the innate recognition of LLO in the activation of the CD4(+) and CD8(+) T cells. Therefore, DDA and LLO can act synergistically to induce the production of a CD8(+) T cell response.

Bystander activation of CD8+ T lymphocytes during experimental mycobacterial infection.

Infection of C57BL/6 mice with Mycobacterium avium leads to the activation of both CD4+ and CD8+ gamma interferon (IFN-gamma)-producing T cells, although the CD8+ cells play no role in protection against infection. Using transfer of different lines of transgenic T cells with T-cell receptors (TCRs) which recognize irrelevant antigens, we show here that transferred CD8+ T cells from two of the three lines were activated to the same degree as the host cells, suggesting that the majority of the IFN-gamma-producing CD8+ T cells of the host represented bystander activation. The third line, specific for the male HY antigen, showed no activation. Activation required the participation of the CD28 coreceptor on T cells and was unaffected by the removal of CD44(hi) (memory phenotype) T cells. The transferred CD8+ T cells proliferated in vivo, although this was not essential for IFN-gamma production. Taken together, these data are highly reminiscent of homeostatic proliferation of TCR transgenic T cells upon transfer to lymphopenic hosts, and suggest low-affinity stimulation through the TCR, possibly by self peptides. The findings are discussed in relation to homeostatic proliferation and their significance in the possible induction of autoimmune disease.

A totally synthetic vaccine of generic structure that targets Toll-like receptor 2 on dendritic cells and promotes antibody or cytotoxic T cell responses.

A simple generic peptide-based vaccine structure that targets Toll-like receptor 2-expressing dendritic cells and causes their activation is described. The vaccines are totally synthetic, serve as their own adjuvant, and are composed of (i) a single helper T cell epitope, (ii) a target epitope that is either recognized by CD8+ T cells or B cells, and (iii) a Toll-like receptor 2-targeting lipid moiety, S-[2,3-bis(palmitoyloxy)propyl]cysteine, that is situated between the peptide epitopes to form a branched configuration. The different CD8+ T cell epitopes examined were from (i) influenza virus, (ii) the intracellular bacterium Listeria monocytogenes, and (iii) ovalbumin as a model tumor antigen. Vaccines containing a B cell epitope from gastrin or luteinizing hormone-releasing hormone as a B cell epitope were also examined for their ability to elicit antibody against the parent hormones. Each of the vaccines was capable of inducing either CD8+ T cell or antibody-mediated immune responses. The lipidated vaccines, but not the nonlipidated vaccines, were able to mediate protection against viral or bacterial infection and mediate prophylactic and therapeutic anticancer activity. The two hormone-based vaccines induced high antibody titers, which in the case of luteinizing hormone-releasing hormone resulted in abrogation of reproductive function. These results highlight the utility of simple, totally synthetic, epitope-based vaccines.

Apoptosis of CD4+ and CD8+ T cells during experimental infection with Mycobacterium avium is controlled by Fas/FasL and Bcl-2-sensitive pathways, respectively.

Both CD4+ and CD8+ T cells from mice infected with Mycobacterium avium suffered a high rate of apoptosis, beginning with the onset of the immune response and culminating in the loss of T cells from the tissues and loss of IFN-gamma production. Fas expression increased over the course of infection on both T cell populations, as did their susceptibility to the induction of apoptosis in vitro by anti-Fas mAb. Nevertheless, although the rate of apoptosis among CD4+ T cells from infected mice was reduced to normal levels in lpr mice with a defective Fas, CD8+ T cells were unaffected, implying that Fas/FasL interaction was not important in these cells in vivo. Conversely, over-expression of B-cell lymphoma-2 (Bcl-2), which is known to protect T cells from apoptosis signalled through the TNF receptor or due to the withdrawal of cytokines, totally protected CD8+ T cells from infected mice but had no effect on CD4+. It is of interest that these two contrasting pathways of T-cell apoptosis operate at the same time during a single infection.

Generalized immunological decline during long-term experimental infection with Mycobacterium avium.

Terminal loss of immune responsiveness in C57BL/10 mice intranasally infected with Mycobacterium avium was observed in both spleen and lung. It was nonspecific and related to the duration of infection, not the age of the mice. While there was loss of total T cells, the remaining cells were less efficient at gamma interferon production.

Identification of an I-Ad restricted peptide on the 65-kilodalton heat shock protein of Mycobacterium avium.

The 65 kilodalton heat shock protein (Hsp65) from mycobacterial species elicits immune responses and in some cases protective immunity. Here we have used a DNA sublibrary approach to identify antigenic fragments of Mycobacterium avium Hsp65 and a synthetic peptide approach to delineate CD4+ T cell determinants. A panel of Hsp65 reactive CD4+ T cell clones was established from lymph node cells obtained from BALB/c mice immunized with recombinant Hsp65. The clones were tested for proliferative reactivity against the products of the DNA sublibrary of the hsp65 gene. A T cell epitope, restricted by the I-Ad molecule, was identified within the C-terminal region of Hsp65 and the minimal epitope (amino acid residues 489-503) delineated using overlapping peptides spanning the C-terminal fragment. Additionally, the CD4+ T cell clone recognizing this epitope also responded to native Hsp65 present in M. avium lysates by both proliferation and cytokine production, indicating that the epitope was present and processed similarly both in the native and the recombinant forms of Hsp65. This sequence identified in BALB/c mice (Hsp65 489-503) is identical in other mycobacteria, notably M. tuberculosis, M. bovis and M. leprae, suggesting the epitope may have wider application in murine models of other mycobacterial infections.

T-cell activation, proliferation and apoptosis in primary Listeria monocytogenes infection.

Listeria monocytogenes infection of mice leads to a rapid expansion of activated T cells, followed by a decline in specific cells once the bacteria are eliminated. In order to define the relationship between T-cell proliferation and activation, and to investigate the role of apoptosis in limiting the expansion, the expression of activation markers, uptake of 5-bromo-2'-deoxyuridine (BrdU) in vivo and the incidence of apoptosis was investigated. Increased numbers of T cells expressing the activated phenotype CD25+, CD44hi and CD62Llo were detected 4 days after infection. Expression of CD25 (IL-2Ralpha chain) on CD4+ and CD8+ T cells peaked at this time and returned to normal by day 7. In contrast, CD44hi and CD62Llo persisted, with the maximum proportion occurring at 7 days after infection. This was accompanied by a burst of in vivo proliferation of CD4+ and CD8+ T cells occurring between day 5 and 7. Apoptosis, which is presumably needed to control this expansion of T cells, also peaked at 7 days after infection. Apoptosis occurred preferentially amongst T cells which had proliferated. Most but not all proliferating T cells had down-regulated their CD62L marker. While most apoptotic T cells were CD62Llo, again not all had down-regulated this marker. Hence, CD25 expression peaked early, but expression of other activation markers, in vivo proliferation and apoptosis coincided after Listeria infection. T cells that had proliferated were over-represented in the apoptotic population.

Oxidised mannan-listeriolysin O conjugates induce Th1/Th2 cytokine responses after intranasal immunisation.

Clearance of infectious organisms does not always require polarised Th1 or Th2 responses and it may be advantageous for both Th1 and Th2 responses to be elicited for effective protection against an invading pathogen. It was the aim of this study to investigate oxidised mannan as a possible Th1/Th2 adjuvant. Oxidised mannan was conjugated to two candidate antigens and delivered intranasally to mice. Immunisation with the oxidised conjugate resulted in significant antigen specific proliferative responses, IL-2, IFN-gamma and IL-4 production when compared to unconjugated controls.

Oxidised mannan as a novel adjuvant inducing mucosal IgA production.

Mannan, oxidatively coupled to recombinant protein antigens, has here been tested as a possible adjuvant for the production of antibody on the mucosa. Given intranasally, but not intraperitoneally, mannan markedly enhanced the production of IgA, IgG1 and IgG2a in the serum, and IgA locally in the lung and at remote mucosal sites, including tears, vaginal and salivary secretions. Oxidative coupling was critical to its action, since neither mannan simply mixed with protein nor mannan-protein conjugates which had been reduced by treatment with sodium borohydride, acted as adjuvants. Oxidatively coupled mannan was compared with the widely studied mucosal adjuvant, cholera toxin (CT). The use of oxidised mannan as an adjuvant induced better responses than CT judged by the induction of IgA in serum, vaginal washings and saliva. Thus, oxidised mannan, which is non-toxic and can be administered without injection, is a suitable adjuvant coupled with protective antigens for vaccinating against a number of infections that occur via the mucous membranes.

Interleukin-2 and loss of immunity in experimental Mycobacterium avium infection.

Experimental infection of mice with a virulent strain of Mycobacterium avium leads to a slowly progressive disease, which we have previously shown culminates in loss of gamma interferon (IFN-gamma) production by T lymphocytes and death of the animals approximately 40 weeks after infection. Here we investigated the changes in T-cell activation, the production of interleukin-2 (IL-2), and the response to IL-2 throughout M. avium infection as a possible explanation for this loss. We found that there is a steady increase in the percentage of T cells expressing activation markers right to the end of infection. However, in vivo T-cell proliferation, measured as a percentage of CD4(+) and CD8(+) cells incorporating 5-bromo-2'-deoxyuridine, initially increased but then remained constant. In the final stages of infection there was a decline in proliferation of activated (CD62L(-)) T cells. Since IL-2 is a major driver of T-cell proliferation, we asked whether this was due to loss of IL-2 responsiveness or production. However, CD25 (IL-2Ralpha) continued to be highly expressed in the terminal stages of infection, and although IL-2 production declined, addition of recombinant IL-2 to cultures could not rescue the final loss of IFN-gamma production.