Mycobacterium bovis bacillus Calmette-Guérin-infected dendritic cells potently activate autologous T cells via a B7 and interleukin-12-dependent mechanism.

Mycobacteria are potent adjuvants, can survive intracellularly and have been safely used for many years as vaccines against tuberculosis and leprosy. They are thus important potential vectors for recombinant vaccines. Many of their adjuvant properties are mediated following phagocytosis by dendritic cells (DC), which are in turn critical for priming naïve T cells. Although the maturation of DC in response to mycobacteria, such as Mycobacterium bovis bacillus Calmette-Guérin (BCG), is well described the subsequent responses of autologous T cells to mycobacterium-infected DC remains uncharacterized. In our experiments DC infected with BCG expressed more co-stimulatory molecules than tumour-necrosis factor-alpha (TNF-alpha) -treated DC and stimulated more potent mixed leucocyte reactions. When autologous T cells were co-cultured with BCG-exposed DC they became highly activated, as determined by display of CD25, CD54 and CD71 on both CD4+ and CD8+ cells. In contrast, the response of T cells to TNF-alpha-matured DC was significantly less. Cytokine production from T cells cultured with BCG-exposed DC was enhanced with elevated secretion of interleukin-2 (IL-2), IL-10 and interferon-gamma (IFN-gamma) and was produced by both CD4+ and CD8+ lymphocytes as determined by intracellular staining. In particular, IFN-gamma secretion was increased from 50 pg/ml to 25 000 pg/ml and IL-10 secretion increased from 20 pg/ml to 300 pg/ml in BCG-exposed DC co-cultures. Blocking antibodies to B7.1 and B7.2 or IL-12 significantly reduced the secretion of IFN-gamma and reductions were also seen in the expression of CD25 and CD71 by CD4+ cells. These data demonstrate that mycobacterially infected DC are particularly potent activators of autologous T cells compared to TNF-alpha-exposed DC and that the resultant T cells are functionally superior.

Soluble interleukin-2 receptors: levels in leprosy, and during and after type 1 (lepra) and type 2 (ENL) reactions.

Twenty-five patients with Type 1 (lepra) and Type 2 (ENL) reactions, were assayed for SIL-2R in serum--before and after treatment for their acute condition--and the results were compared with 10 normal healthy adults and 20 patients of leprosy per se. Classification of each subject into different leprosy groups, and into various types and subtypes of reactions, was done according to standard criteria, prior to inclusion into the study. Detailed statistical evaluation of the data revealed significantly higher levels of SIL-2R in all leprosy patients, as compared to normal controls, with higher levels in the multibacillary groups as compared to the paucibacillary group. SIL-2Rs appeared higher in Type 1 upgrading reaction than in other forms of reaction, though this was not statistically significant. There was no significant change in levels following treatment and clinical remission.

Flow cytometric analysis of CD2 modulation on human peripheral blood T lymphocytes by Dharmendra preparation of Mycobacterium leprae.

It has been reported previously that Mycobacterium leprae modulated CD2 on human peripheral blood T lymphocytes and that this modulation was accompanied by a marked reduction in the proliferative response of these cells to mitogens and antigens. In this study, we report that treatment of peripheral blood mononuclear cells from healthy individuals with Dharmendra preparation of M. leprae inhibited their ability to form rosettes with sheep red blood cells. Flow cytometric analysis of Dharmendra lepromin-treated cells showed that, in addition to CD2, CD4 and CD8 were modulated while the surface expression of CD3 was not affected. The specificity of CD2 modulation was confirmed by similar effects of Dharmendra lepromin on thymocytes and lymph node cells from human CD2 transgenic mice. The modulatory effect of Dharmendra lepromin was not observed at lower temperatures. Dharmendra lepromin treatment of activated T cells resulted in reduced binding of monoclonal antibodies to IL-2R and D66 epitope of CD2. The modulatory effects were not observed with Dharmendra preparation of BCG or other preparations of M. leprae. Our results indicate that certain M. leprae factor(s) specifically modulate(s) CD2, CD4, CD8 and IL-2R but not CD3 on T lymphocytes. The suppressive effect of Dharmendra lepromin on the T-cell proliferative response reported earlier may be explained by its modulatory effect on a number of T-cell surface molecules.

Target cell lysis and IL-2 secretion by gamma/delta T lymphocytes after activation with bacteria.

Peripheral blood T lymphocytes from healthy donors were stimulated with Mycobacterium tuberculosis in vitro and afterward analyzed phenotypically. Marked expansion of the gamma/delta T cell population (3- to 21-fold) was observed in 15/21 donors 7 to 10 days after stimulation. In addition to M. tuberculosis, Mycobacterium leprae (six of eight) as well as the gram-positive bacteria, Staphylococcus aureus (two of six), group A streptococci (seven of nine), and Listeria monocytogenes (four of eight) augmented gamma/delta TCR expression in peripheral blood T cells of many donors. gamma/delta T lymphocytes expressed IL-2R and secreted IL-2 upon restimulation with M. tuberculosis. Stimulation with M. tuberculosis evoked specific cytolytic activities in gamma/delta T lymphocytes because: gamma/delta T cells lysed M. tuberculosis pulsed but not unpulsed targets; high concentrations of TCR delta 1 mAb facilitated killing of unpulsed target cells; and low doses of anti-TCR delta 1 mAb blocked killing of pulsed targets. Furthermore, gamma/delta T cells from four donors, after activation with M. tuberculosis or with group A streptococci, respectively, only lysed targets pulsed with the homologous agents, whereas in other donors some cross-reactivity was observed. We conclude that, upon contact with mycobacteria and perhaps other microorganisms, gamma/delta T cells are activated which contribute to immunity against infection via IL-2 secretion and specific target cell lysis.

Inhibition of human lymphoproliferative responses by mycobacterial phenolic glycolipids.

The effect of mycobacterial phenolic glycolipids from Mycobacterium leprae, M. bovis BCG, and M. kansasii on in vitro proliferative responses by human blood mononuclear cells from healthy BCG vaccinees was investigated. All three phenolic glycolipids inhibited proliferation in a concentration-dependent manner. Inhibition was independent of the stimulus used and involved neither antigen-presenting cells nor antigen-specific CD8+ suppressor T cells. It was concluded that the phenomenon may be a general property of mycobacterial phenolic glycolipids, perhaps analogous to the growth-modulating properties of gangliosides. Despite the lack of specificity of inhibition in vitro, de facto specificity may occur in vivo by virtue of the localization of glycolipid in the leprosy lesions.

A transient rise in agalactosyl IgG correlating with free interleukin 2 receptors, during episodes of erythema nodosum leprosum.

The proportion of oligosaccharide chains on the Fc fragment of IgG which terminate with N-acetylglucosamine and not galactose (%GO) has previously been shown to be raised in rheumatoid arthritis (RA), Crohn's disease (CD) and tuberculosis (Tb), but to be normal in sarcoidosis (SA), and in both lepromatous and tuberculoid leprosy. However we have now studied %GO in sequential serum samples collected from lepromatous leprosy patients undergoing episodes of erythema nodosum leprosum (ENL). During ENL %GO is transiently raised, and this rise parallels an increase in circulating interleukin 2 receptors (IL-2R). These findings confirm that changes in T cell function occur during ENL. Moreover it appears that %GO rises when there is, simultaneously, T-cell-mediated tissue damage and an acute phase response (RA, CD, Tb, ENL), but not when there is an acute phase response without major T cell involvement, or chronic T cell activity alone (SA, and tuberculoid leprosy). We suggest therefore that %GO is an indicator of a type of T cell activity with broad immunopathological implications.