Anti-TNF immunotherapy reduces CD8+ T cell-mediated antimicrobial activity against Mycobacterium tuberculosis in humans.

The incidence of tuberculosis is increased during treatment of autoimmune diseases with anti-TNF antibodies. This is a significant clinical complication, but also provides a unique model to study immune mechanisms in human tuberculosis. Given the key role for cell-mediated immunity in host defense against Mycobacterium tuberculosis, we hypothesized that anti-TNF treatment impairs T cell-directed antimicrobial activity. Anti-TNF therapy reduced the expression in lymphocytes of perforin and granulysin, 2 components of the T cell-mediated antimicrobial response to intracellular pathogens. Specifically, M. tuberculosis-reactive CD8+CCR7-CD45RA+ effector memory T cells (TEMRA cells) expressed the highest levels of granulysin, lysed M. tuberculosis, and infected macrophages and mediated an antimicrobial activity against intracellular M. tuberculosis. Furthermore, TEMRA cells expressed cell surface TNF and bound the anti-TNF therapeutic infliximab in vitro, making them susceptible to complement-mediated lysis. Immune therapy with anti-TNF was associated with reduced numbers of CD8+ TEMRA cells and decreased antimicrobial activity against M. tuberculosis, which could be rescued by the addition of CD8+ TEMRA cells. These results suggest that anti-TNF therapy triggers a reduction of CD8+ TEMRA cells with antimicrobial activity against M. tuberculosis, providing insight into the mechanism whereby key effector T cell subsets contribute to host defense against tuberculosis.

Macrophages acquire neutrophil granules for antimicrobial activity against intracellular pathogens.

A key target of many intracellular pathogens is the macrophage. Although macrophages can generate antimicrobial activity, neutrophils have been shown to have a key role in host defense, presumably by their preformed granules containing antimicrobial agents. Yet the mechanism by which neutrophils can mediate antimicrobial activity against intracellular pathogens such as Mycobacterium tuberculosis has been a long-standing enigma. We demonstrate that apoptotic neutrophils and purified granules inhibit the growth of extracellular mycobacteria. Phagocytosis of apoptotic neutrophils by macrophages results in decreased viability of intracellular M. tuberculosis. Concomitant with uptake of apoptotic neutrophils, granule contents traffic to early endosomes, and colocalize with mycobacteria. Uptake of purified granules alone decreased growth of intracellular mycobacteria. Therefore, the transfer of antimicrobial peptides from neutrophils to macrophages provides a cooperative defense strategy between innate immune cells against intracellular pathogens and may complement other pathways that involve delivery of antimicrobial peptides to macrophages.

Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response.

In innate immune responses, activation of Toll-like receptors (TLRs) triggers direct antimicrobial activity against intracellular bacteria, which in murine, but not human, monocytes and macrophages is mediated principally by nitric oxide. We report here that TLR activation of human macrophages up-regulated expression of the vitamin D receptor and the vitamin D-1-hydroxylase genes, leading to induction of the antimicrobial peptide cathelicidin and killing of intracellular Mycobacterium tuberculosis. We also observed that sera from African-American individuals, known to have increased susceptibility to tuberculosis, had low 25-hydroxyvitamin D and were inefficient in supporting cathelicidin messenger RNA induction. These data support a link between TLRs and vitamin D-mediated innate immunity and suggest that differences in ability of human populations to produce vitamin D may contribute to susceptibility to microbial infection.

Inverse correlation of maturity and antibacterial activity in human dendritic cells.

Dendritic cells (DCs) are a key part of host defense against microbial pathogens, being part of the innate immune system, but also instructing the adaptive T cell response. This study was designed to evaluate whether human DCs directly contribute to innate immunity by killing intracellular bacteria, using tuberculosis as a model. DCs were detected in bronchoalveolar lavage samples indicating that DCs are available for immediate interaction with Mycobacterium tuberculosis (M. Tb) after inhalation of the pathogen. The phenotype of DC in bronchoalveolar lavage closely resembles monocyte-derived immature DC (iDC) according to the expression of CD1a, CD83, and CCR7. The antimicrobial activity of iDC against intracellular M. Tb inversely correlated with TNF-alpha-release and was enhanced by treatment with anti-TNF-alpha Abs. Differentiation of iDC into mature DC by addition of TNF-alpha or activation via Toll-like receptors further reduced killing of M. Tb. The antibacterial activity against intracellular M. Tb of all DCs was significantly lower than alveolar macrophages. Therefore, the maintenance of a pool of DCs at the site of disease activity in tuberculosis, and the maturation of these DC by TNF-alpha provides a mechanism by which M. Tb escapes the innate immune system.

Use of genetic profiling in leprosy to discriminate clinical forms of the disease.

Leprosy presents as a clinical and immunological spectrum of disease. With the use of gene expression profiling, we observed that a distinction in gene expression correlates with and accurately classifies the clinical form of the disease. Genes belonging to the leukocyte immunoglobulin-like receptor (LIR) family were significantly up-regulated in lesions of lepromatous patients suffering from the disseminated form of the infection. In functional studies, LIR-7 suppressed innate host defense mechanisms by shifting monocyte production from interleukin-12 toward interleukin-10 and by blocking antimicrobial activity triggered by Toll-like receptors. Gene expression profiles may be useful in defining clinical forms of disease and providing insights into the regulation of immune responses to pathogens.

Use of genetic profiling in leprosy to discriminate clinical forms of the disease

Leprosy presents as a clinical and immunological spectrum of disease. With the use of gene expression profiling, we observed that a distinction in gene expression correlates with and accurately classifies the clinical form of the disease. Genes belonging to the leukocyte immunoglobulin-like receptor (LIR) family were significantly up-regulated in lesions of lepromatous patients suffering from the disseminated form of the infection. In functional studies, LIR-7 suppressed innate host defense mechanisms by shifting monocyte production from interleukin-12 toward interleukin-10 and by blocking antimicrobial activity triggered by Toll-like receptors. Gene expression profiles may be useful in defining clinical forms of disease and providing insights into the regulation of immune responses to pathogens.

Expression of the glycolytic gapA operon in Bacillus subtilis: differential syntheses of proteins encoded by the operon.

Glycolysis is one of the central routes of carbon catabolism in Bacillus subtilis. Several glycolytic enzymes, including the key enzyme glyceraldehyde-3-phosphate dehydrogenase, are encoded in the hexacistronic gapA operon. Expression of this operon is induced by a variety of sugars and amino acids. Under non-inducing conditions, expression is repressed by the CggR repressor protein, the product of the promoter-proximal gene of the operon. Here, it is shown that the amount of glyceraldehyde-3-phosphate dehydrogenase encoded by the second gene of the operon exceeds that of the CggR repressor by about 100-fold. This differential synthesis was attributed to an mRNA processing event that takes place at the 3' end of the cggR open reading frame and to differential segmental stabilities of the resulting cleavage products. The mRNA specifying the truncated cggR gene is quickly degraded, whereas the downstream processing products encompassing gapA are quite stable. This increased stability is conferred by the presence of a stem-loop structure at the 5' end of the processed mRNAs. Mutations were introduced in the region of the cleavage site. A mutation affecting the stability of the stem-loop structure immediately downstream of the processing site had two effects. First, the steady-state transcript pattern was drastically shifted towards the primary transcripts; second, the stability of the processed mRNA containing the destabilized stem-loop structure was strongly decreased. This results in a reduction of the amount of glyceraldehyde-3-phosphate dehydrogenase in the cell. It is concluded that mRNA processing is involved in differential syntheses of the proteins encoded by the gapA operon.

Insufficient expression of the ilv-leu operon encoding enzymes of branched-chain amino acid biosynthesis limits growth of a Bacillus subtilis ccpA mutant.

Bacillus subtilis ccpA mutant strains exhibit two distinct phenotypes: they are defective in catabolite repression, and their growth on minimal media is strongly impaired. This growth defect is largely due to a lack of expression of the gltAB operon. However, growth is impaired even in the presence of glutamate. Here, we demonstrate that the ccpA mutant strain needs methionine and the branched-chain amino acids for optimal growth. The control of expression of the ilv-leu operon by CcpA provides a novel regulatory link between carbon and amino acid metabolism.