Vaccine-induced inflammation and inflammatory monocytes promote CD4+ T cell-dependent immunity against murine salmonellosis.

Prior infection can generate protective immunity against subsequent infection, although the efficacy of such immunity can vary considerably. Live-attenuated vaccines (LAVs) are one of the most effective methods for mimicking this natural process, and analysis of their efficacy has proven instrumental in the identification of protective immune mechanisms. Here, we address the question of what makes a LAV efficacious by characterising immune responses to a LAV, termed TAS2010, which is highly protective (80-90%) against lethal murine salmonellosis, in comparison with a moderately protective (40-50%) LAV, BRD509. Mice vaccinated with TAS2010 developed immunity systemically and were protected against gut-associated virulent infection in a CD4+ T cell-dependent manner. TAS2010-vaccinated mice showed increased activation of Th1 responses compared with their BRD509-vaccinated counterparts, leading to increased Th1 memory populations in both lymphoid and non-lymphoid organs. The optimal development of Th1-driven immunity was closely correlated with the activation of CD11b+Ly6GnegLy6Chi inflammatory monocytes (IMs), the activation of which can be modulated proportionally by bacterial load in vivo. Upon vaccination with the LAV, IMs expressed T cell chemoattractant CXCL9 that attracted CD4+ T cells to the foci of infection, where IMs also served as a potent source of antigen presentation and Th1-promoting cytokine IL-12. The expression of MHC-II in IMs was rapidly upregulated following vaccination and then maintained at an elevated level in immune mice, suggesting IMs may have a role in sustained antigen stimulation. Our findings present a longitudinal analysis of CD4+ T cell development post-vaccination with an intracellular bacterial LAV, and highlight the benefit of inflammation in the development of Th1 immunity. Future studies focusing on the induction of IMs may reveal key strategies for improving vaccine-induced T cell immunity.

CD4+ T cell immunity to Salmonella is transient in the circulation.

While Salmonella enterica is seen as an archetypal facultative intracellular bacterial pathogen where protection is mediated by CD4+ T cells, identifying circulating protective cells has proved very difficult, inhibiting steps to identify key antigen specificities. Exploiting a mouse model of vaccination, we show that the spleens of C57BL/6 mice vaccinated with live-attenuated Salmonella serovar Typhimurium (S. Typhimurium) strains carried a pool of IFN-γ+ CD4+ T cells that could adoptively transfer protection, but only transiently. Circulating Salmonella-reactive CD4+ T cells expressed the liver-homing chemokine receptor CXCR6, accumulated over time in the liver and assumed phenotypic characteristics associated with tissue-associated T cells. Liver memory CD4+ T cells showed TCR selection bias and their accumulation in the liver could be inhibited by blocking CXCL16. These data showed that the circulation of CD4+ T cells mediating immunity to Salmonella is limited to a brief window after which Salmonella-specific CD4+ T cells migrate to peripheral tissues. Our observations highlight the importance of triggering tissue-specific immunity against systemic infections.

Optimal protection against Salmonella infection requires noncirculating memory.

While CD4 Th1 cells are required for resistance to intramacrophage infections, adoptive transfer of Th1 cells is insufficient to protect against Salmonella infection. Using an epitope-tagged vaccine strain of Salmonella, we found that effective protection correlated with expanded Salmonella-specific memory CD4 T cells in circulation and nonlymphoid tissues. However, naive mice that previously shared a blood supply with vaccinated partners lacked T cell memory with characteristics of tissue residence and did not acquire robust protective immunity. Using a YFP-IFN-γ reporter system, we identified Th1 cells in the liver of immunized mice that displayed markers of tissue residence, including P2X7, ARTC2, LFA-1, and CD101. Adoptive transfer of liver memory cells after ARTC2 blockade increased protection against highly virulent bacteria. Taken together, these data demonstrate that noncirculating memory Th1 cells are a vital component of immunity to Salmonella infection and should be the focus of vaccine strategies.

Biomechanics of T Cell Dysfunctions in Chronic Diseases.

Understanding the mechanisms behind T cell dysfunctions during chronic diseases is critical in developing effective immunotherapies. As demonstrated by several animal models and human studies, T cell dysfunctions are induced during chronic diseases, spanning from infections to cancer. Although factors governing the onset and the extent of the functional impairment of T cells can differ during infections and cancer, most dysfunctional phenotypes share common phenotypic traits in their immune receptor and biophysical landscape. Through the latest developments in biophysical techniques applied to explore cell membrane and receptor-ligand dynamics, we are able to dissect and gain further insights into the driving mechanisms behind T cell dysfunctions. These insights may prove useful in developing immunotherapies aimed at reinvigorating our immune system to fight off infections and malignancies more effectively. The recent success with checkpoint inhibitors in treating cancer opens new avenues to develop more effective, targeted immunotherapies. Here, we highlight the studies focused on the transformation of the biophysical landscape during infections and cancer, and how T cell biomechanics shaped the immunopathology associated with chronic diseases.

Potential of a simplified measurement scheme and device structure for a low cost label-free point-of-care capacitive biosensor.

A simplified measurement scheme and device structure aiming at developing a low cost, label-free, point-of-care capacitive biosensor were investigated. The detection principle is the increase of low frequency capacitance between two planar Al electrodes observed after antibody-antigen interaction. The electrodes, deposited on oxidized Si wafers, were covered with an antibody layer, with and without using self-assembled thiol monolayer. Immunoglobulin G (IgG) and cardiac troponin T (TnT) were used as analytes to asses this proposal. The device was able to detect successfully TnT levels in the range 0.07 to 6.83ng/mL in human serum from patients with cardiac diseases and in the range 0.01ng/mL to 5ng/mL for TnT in phosphate buffer saline. An equivalent circuit model able to reproduce the general behavior of experimental capacitance versus frequency curves was presented. The investigated features that have potential to reduce costs and simplify measurements were: use of single, low frequency (1kHz) measurement signal, within the range of low cost portable capacitance meters; employment of a lower cost electrode material, aluminum, instead of gold electrodes; and use of simple and miniaturized planar two-electrodes arrangement, thus making a portable system for point-of-care applications.