SLAMF1 signaling induces Mycobacterium tuberculosis uptake leading to endolysosomal maturation in human macrophages

Tuberculosis dates back to ancient times but it is not a problem of the past. Each year, millions of people die from tuberculosis. After inhalation of infectious droplet nuclei, Mycobacterium tuberculosis reaches the lungs where it can manipulate the immune system and survive within host macrophages, establishing a persistent infection. The signaling lymphocytic activation molecule family member 1 (SLAMF1) is a self-ligand receptor that can internalize gram-negative bacteria and regulate macrophages' phagosomal functions. In tuberculosis, SLAMF1 promotes Th1-protective responses. In this work, we studied the role of SLAMF1 on macrophages' functions during M. tuberculosis infection. Our results showed that both M. tuberculosis and IFN-γ stimulation induce SLAMF1 expression in macrophages from healthy donor and Tohoku Hospital Pediatrcs-1 cells. Costimulation through SLAMF1 with an agonistic antibody resulted in an enhanced internalization of M. tuberculosis by macrophages. Interestingly, we found that SLAMF1 interacts with M. tuberculosis and colocalizes with the bacteria and with early and late endosomes/lysosomes markers (EEA1 and LAMP2), suggesting that SLAMF1 recognize M. tuberculosis and participate in the endolysosomal maturation process. Notably, increased levels of SLAMF1 were detected in CD14 cells from pleural effusions of tuberculosis patients, indicating that SLAMF1 might have an active function at the site of infection. Taken together, our results provide evidence that SLAMF1 improves the uptake of M. tuberculosis by human monocyte-derived macrophages.

Microbial sensor for drug susceptibility testing of Mycobacterium tuberculosis

AIMS

Drug susceptibility testing (DST) of clinical isolates of Mycobacterium tuberculosis is critical in treating tuberculosis. We demonstrate the possibility of using a microbial sensor to perform DST of M. tuberculosis and shorten the time required for DST.

METHODS AND RESULTS

The sensor is made of an oxygen electrode with M. tuberculosis cells attached to its surface. This sensor monitors the residual oxygen consumption of M. tuberculosis cells after treatment with anti-TB drugs with glycerine as a carbon source. In principle, after drug pretreatment for 4-5 days, the response differences between the sensors made of drug-sensitive isolates are distinguishable from the sensors made of drug-resistant isolates. The susceptibility of the M. tuberculosis H37Ra strain, its mutants and 35 clinical isolates to six common anti-TB drugs: rifampicin, isoniazid, streptomycin, ethambutol, levofloxacin and para-aminosalicylic acid were tested using the proposed method. The results agreed well with the gold standard method (LJ) and were determined in significantly less time. The whole procedure takes approximately 11 days and therefore has the potential to inform clinical decisions.

CONCLUSIONS

To our knowledge, this is the first study that demonstrates the possible application of a dissolved oxygen electrode-based microbial sensor in M. tuberculosis drug resistance testing. This study used the microbial sensor to perform DST of M. tuberculosis and shorten the time required for DST.

SIGNIFICANCE AND IMPACT OF THE STUDY

The overall detection result of the microbial sensor agreed well with that of the conventional LJ proportion method and takes less time than the existing phenotypic methods. In future studies, we will build an O₂ electrode array microbial sensor reactor to enable a high-throughput drug resistance analysis.

From sensing to shaping microbiota: insights into the role of NOD2 in intestinal homeostasis and progression of Crohn's disease

NOD2 was the first susceptibility gene identified for Crohn's disease (CD), one of the major forms of inflammatory bowel disease (IBD). The field of NOD2 research has opened up many questions critical to understanding the complexities of microbiota-host interactions. In addition to sensing its specific bacterial components as a cytosolic pattern recognition receptor, NOD2 also appears to shape the colonization of intestinal microbiota. Activated NOD2 triggers downstream signaling cascades exampled by the NF-κB pathway to induce antimicrobial activities, however, defective or loss of NOD2 functions incur a similarly activated inflammatory response. Additional studies have identified the involvement of NOD2 in protection against non-microbiota-related intestinal damages as well as extraintestinal infections. We survey recent molecular and genetic studies of NOD2-mediated bacterial sensing and immunological modulation, and integrate evidence to suggest a highly reciprocal but still poorly understood cross talk between enteric microbiota and host cells.

Caspase recruitment domain-containing sensors and adaptors in intestinal innate immunity

PURPOSE OF REVIEW

The present review discusses the physiological functions of selected caspase recruitment domain (CARD)-containing sensor and adaptor proteins and their role in the pathogenesis of intestinal diseases.

RECENT FINDINGS

Myeloid and lymphoid cells as well as intestinal epithelial cells express several intracellular CARD-containing proteins. CARD-containing sensors, particularly NOD1 (CARD4), NOD2 (CARD15) and IPAF (CARD12), have an important role in the detection of conserved microbial structures of invading microbial pathogens. Upon ligand recognition and activation, the sensors interact through CARD domains with downstream CARD-containing adaptors including CARD9, RIP2 (CARD3) and ASC (CARD5). Recent data suggest that multiple signaling pathways from Toll-like receptors and non-Toll-receptor pathways converge on these adaptor proteins and that their functions are crucial for the initiation of innate immune responses to invading microbial pathogens.

SUMMARY

CARD-containing adaptors and sensors represent an important family of molecules involved in innate host defense against gastrointestinal pathogens and in the regulation of inflammatory responses, suggesting that further insights into their physiological functions may yield new pharmacological strategies for treating intestinal inflammatory conditions.

Sensor molecules in intestinal innate immunity against bacterial infections

PURPOSE OF REVIEW

Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD)-containing proteins are innate immune sensors for microbial signature molecules. This review highlights new insights into the functions of these sensors in intestinal physiology.

RECENT FINDINGS

TLRs are membrane bound and survey the extracellular space for microbe-derived molecules, while NOD-containing proteins are cytoplasmic and detect microbial molecules in the cytoplasm. Most microbial sensors recognize components of the bacterial cell wall and its appendages. For example, TLR4 detects lipopolysaccharide in the Gram-negative bacterial cell wall. TLR5 recognizes flagellin, a component of bacterial flagella required for motility. NOD1 recognizes diaminopimelic acid-containing dipeptide or tripeptide motifs in the Gram-positive bacterial cell wall, while NOD2 detects muramyl dipeptide, a ubiquitous cell wall peptidoglycan motif. These sensors are important for host defense against gastrointestinal pathogens. Thus, TLR4 is required for Salmonella eradication, NOD1 contributes to controlling Helicobacter pylori infection, and NOD2 is involved in mucosal defense against Listeria monocytogenes. These sensors also regulate mucosal inflammation independent of pathogen infections.

SUMMARY

Toll-like receptors and nucleotide-binding oligomerization domain-containing proteins not only play critical roles in host defense against known gastrointestinal bacterial pathogens, but also contribute to mucosal homeostasis in the apparent absence of such pathogens.