Gut-resident CX3CR1hi macrophages induce tertiary lymphoid structures and IgA response in situ

Intestinal mononuclear phagocytes (MPs) are composed of heterogeneous dendritic cell (DC) and macrophage subsets necessary for the initiation of immune response and control of inflammation. Although MPs in the normal intestine have been extensively studied, the heterogeneity and function of inflammatory MPs remain poorly defined. We performed phenotypical, transcriptional, and functional analyses of inflammatory MPs in infectious Salmonella colitis and identified CX3CR1⁺ MPs as the most prevalent inflammatory cell type. CX3CR1⁺ MPs were further divided into three distinct populations, namely, Nos2 ⁺CX3CR1^lo, Ccr7 ⁺CX3CR1^int (lymph migratory), and Cxcl13 ⁺CX3CR1^hi (mucosa resident), all of which were transcriptionally aligned with macrophages and derived from monocytes. In follow-up experiments in vivo, intestinal CX3CR1⁺ macrophages were superior to conventional DC1 (cDC1) and cDC2 in inducing Salmonella-specific mucosal IgA. We next examined spatial organization of the immune response induced by CX3CR1⁺ macrophage subsets and identified mucosa-resident Cxcl13 ⁺CX3CR1^hi macrophages as the antigen-presenting cells responsible for recruitment and activation of CD4⁺ T and B cells to the sites of Salmonella invasion, followed by tertiary lymphoid structure formation and the local pathogen-specific IgA response. Using mice we developed with a floxed Ccr7 allele, we showed that this local IgA response developed independently of migration of the Ccr7 ⁺CX3CR1^int population to the mesenteric lymph nodes and contributed to the total mucosal IgA response to infection. The differential activity of intestinal macrophage subsets in promoting mucosal IgA responses should be considered in the development of vaccines to prevent Salmonella infection and in the design of anti-inflammatory therapies aimed at modulating macrophage function in inflammatory bowel disease.

Neuro-innate immune interactions in gut mucosal immunity

The gastrointestinal (GI) tract performs a set of vital physiological functions related to food and water consumption. To help regulate these complex physiological processes, the GI tract is innervated by extensive neural networks. The GI tract also serves as the largest immune organ aimed to protect hosts from harmful microbes and toxins ingested with food. It emerges that the enteric nervous and immune systems are highly integrated to optimize digestion while reinforcing immune protection. In this review, we will discuss key cellular players involved in the neuro-immune interactions within the GI mucosa with the focus on the recently uncovered neural pathways that regulate mucosal immunity in a context relevant to GI health and disease.

'Nervous' Immunity: Walking the Tightrope

There is a major gap in our understanding of how the intestinal immune and nervous systems are integrated to regulate protective adaptations to enteric infections while maintaining tissue homeostasis. Three recent complementary reports published in Cell (2020) provide new mechanistic insights into how this enteric neuro-immune crosstalk may occur.

MALDI-TOF mass spectrometry proteomic based identification of clinical bacterial isolates

BACKGROUND & OBJECTIVES

Pathogenic bacteria often cause life threatening infections especially in immunocompromised individuals. Therefore, rapid and reliable species identification is essential for a successful treatment and disease management. We evaluated a rapid, proteomic based technique for identification of clinical bacterial isolates by protein profiling using matrix-assisted laser desorption-ionization time - of - flight mass spectrometry (MALDI-TOF MS).

METHODS

Freshly grown bacterial isolates were selected from culture plates. Ethanol/formic acid extraction procedure was carried out, followed by charging of MALDI target plate with the extract and overlaying with α-cyano-4 hydroxy-cinnamic acid matrix solution. Identification was performed using the MALDI BioTyper 1.1, software for microbial identification (Bruker Daltonik GmbH, Bremen, Germany).

RESULTS

A comparative analysis of 82 clinical bacterial isolates using MALDI -TOF MS and conventional techniques was carried out. Amongst the clinical isolates, the accuracy at the species level for clinical isolates was 98.78%. One out of 82 isolates was not in accordance with the conventional assays because MALDI-TOF MS established it as Streptococcus pneumoniae and conventional methods as Streptococcus viridans.

INTERPRETATION & CONCLUSIONS

MALDI - TOF MS was found to be an accurate, rapid, cost-effective and robust system for identification of clinical bacterial isolates. This innovative approach holds promise for earlier therapeutic intervention leading to better patient care.

The enduring tale of T cells in HIV immunopathogenesis

HIV continues to be a major health problem worldwide even today. Owing to the intricate nature of its interactions with the immune system, HIV has remained an enigma that cleverly utilizes the host machinery to survive. Its ability to evade the host immune system, at both levels, innate and adaptive, allows the pathogen to replicate and transmit from one host to another. It has been shown that HIV has multipronged effects especially on the adaptive immunity, with CD4+ T cells being the worst affected T cell populations. Various analyses have revealed that the exposure to HIV results in clonal expansion and excessive activation of the immune system. Also, an abnormal process of differentiation has been observed suggestive of an alteration and blocks in the maturation of various T cell subsets. Additionally, HIV has shown to accelerate immunosenescence and exhaustion of the overtly activated T cells. Apart from causing phenotypic changes, HIV has adverse effects on the functional aspect of the immune system, with evidences implicating it in the loss of the capacity of T cells to secrete various antiviral cytokines and chemokines. However, there continues to be many aspects of the immunopathogenesis of HIV that are still unknown and thus require further research to convert the malaise of HIV into a manageable epidemic.

Rapid identification of clinical mycobacterial isolates by protein profiling using matrix assisted laser desorption ionization-time of flight mass spectrometry

PURPOSE

The purpose of this study was to evaluate the identification of Mycobacterium tuberculosis which is often plagued with ambiguity. It is a time consuming process requiring 4-8 weeks after culture positivity, thereby delaying therapeutic intervention. For a successful treatment and disease management, timely diagnosis is imperative. We evaluated a rapid, proteomic based technique for identification of clinical mycobacterial isolates by protein profiling using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).

MATERIALS AND METHODS

Freshly grown mycobacterial isolates were used. Acetonitrile/trifluoroacetic acid extraction procedure was carried out, following which cinnamic acid charged plates were subjected to identification by MALDI-TOF MS.

RESULTS

A comparative analysis of 42 clinical mycobacterial isolates using the MALDI-TOF MS and conventional techniques was carried out. Among these, 97.61% were found to corroborate with the standard methods at genus level and 85.36% were accurate till the species level. One out of 42 was not in accord with the conventional assays because MALDI-TOF MS established it as Mycobacterium tuberculosis (log (score)>2.0) and conventional methods established it to be non-tuberculous Mycobacterium.

CONCLUSIONS

MALDI-TOF MS was found to be an accurate, rapid, cost effective and robust system for identification of mycobacterial species. This innovative approach holds promise for early therapeutic intervention leading to better patient care.

Loss of CD127 & increased immunosenescence of T cell subsets in HIV infected individuals

Background & objectives:

HIV infection is characterized by a perturbation in T cell homeostasis, leading to alteration in T cell subsets. In addition to alteration in differentiation, HIV infection also leads to change in T cell survival and regenerative capacity, as suggested by differential expression of CD127 and CD57. We evaluated the expression patterns of CD127 and CD57 on CD4 and CD8 effector, memory and naïve T cell subsets in HIV-infected and uninfected individuals.

Methods:

We characterized T cell subsets based on expression of these markers, and compared their expression pattern in HIV infected subjects and uninfected controls. We further assessed therapy generated changes in these subsets and expression of CD127 and CD57 on them.

Results:

There was a generalized decrease in naïve CD4 and CD8 T cells in HIV infected subjects. These changes in T cell subset distribution were related to antigen load. CD127 expression was significantly reduced in T cells from HIV infected subject. In association to this, HIV infected subjects had higher percentage of T cell subsets expressing CD57. Increased CD57 and reduced CD127 expression correlated with plasma viraemia and CD8 T cell activation state. Incomplete restoration of T cell subset proportions was observed, despite suppression of viral replication and increase in CD4 T cell counts. Further, the improvement was more pronounced in CD127 expression.

Interpretation & conclusions:

HIV infected subjects have reduced T cell regenerative capacity along with increased senescence, highlighting decreased proliferation and effector activities.

Altered T cell differentiation associated with loss of CD27 and CD28 in HIV infected Indian individuals

BACKGROUND

HIV-1 infection is associated with depletion of naïve T cell subsets and skewed T cell differentiation and maturation, leading to accumulation of T cells at intermediate and end stages of differentiation. CD27 and CD28 expression have been utilized in assessing these population subsets.

METHODS

We characterized T cell subsets based on expression of CD45RA, CCR7, CD27, and CD28 and compared these subsets in HIV-1 infected Indian subjects and uninfected controls.

RESULTS

HIV-1 infection was associated with an increase in effector and memory T cell subsets and a concomitant decrease in naïve T cells. HIV-1 infected subjects showed accumulation of intermediate CD8 T cell (CD27+CD28-) differentiation subsets, whereas CD4 T cells progressed to late stage differentiation (CD27-CD28-). These subsets were negatively associated with CD4 T cell counts and positively associated with plasma viremia. CD57, an immunosenescence marker, was also increased on T cell subsets from HIV-1 infected individuals. Antiretroviral therapy resulted in partial restoration of differentiation status.

CONCLUSION

Persistent HIV-1 replication and chronic immune activation, along with altered cytokine secretion profile, lead to impaired T cell differentiation and maturation. Detailed understanding of factors associated with differentiation defects in HIV-1 infected Indian individuals will strongly assist in Indian HIV-1 vaccine efforts and add to our knowledge of HIV-1 subtype C pathogenesis.

Expression of a functional single-chain antibody via Corynebacterium pseudodiphtheriticum

Antibody-based therapeutics are effective against conditions ranging from acute infections to malignancy. They may prove crucial in combating bioterrorism and responding to drug-resistant and emerging pathogens. At present the cost of producing therapeutic monoclonal antibodies is between $1,000 to $6,000 per gram. The need to administer antibodies parenterally at frequent intervals further drives the cost of this treatment. Here we present an antibody delivery system, termed paratransgenesis, with the potential to overcome these limitations. The paratransgenic approach involves genetically transforming a commensal or symbiont bacterium to express foreign molecules that target pathogens. We describe transformation of Corynebacterium pseudodiptheriticum, a commensal bacterium found in the human respiratory tract, to express a murine single-chain antibody binding progesterone. The antibody was functional and bound specifically to progesterone in a concentration-dependent manner. This marker antibody system is the precursor to development of expression systems producing recombinant humanized single-chain antibodies. Studies are in progress evaluating fitness, transgene stablility, and pathogenecity of the genetically engineered C. pseudodiptheriticum. We anticipate developing a repertoire of expressed molecules targeting infectious agents and surface epitopes of pulmonary mass lesions. If expression systems for anti-pathogen molecules in C. pseudodiptheriticum and other respiratory commensal bacteria can be optimized, these bacteria have the potential for a range of therapeutic and prophylactic applications.