Growth arrest-specific protein 6 (GAS6) is a soluble agonist of the TYRO3, AXL, MERTK (TAM) family of receptor tyrosine kinases identified to have anti-inflammatory, neuroprotective, and promyelinating properties. During experimental autoimmune encephalomyelitis (EAE), wild-type (WT) mice demonstrate a significant induction of Gas6, Axl, and Mertk but not Pros1 or Tyro3 mRNA. We tested the hypothesis that intracerebroventricular delivery of GAS6 directly into the CNS of WT mice during myelin oligodendrocyte glycoprotein (MOG)-induced EAE would improve the clinical course of disease relative to artificial CSF (ACSF)-treated mice. GAS6 did not delay disease onset, but significantly reduced the clinical scores during peak and chronic EAE. Mice receiving GAS6 for 28 d had preserved SMI31 ϩ neurofilament immunoreactivity, significantly fewer SMI32 ϩ axonal swellings and spheroids and less demyelination relative to ACSF-treated mice. Alternate-day subcutaneous IFN␤ injection did not enhance GAS6 treatment effectiveness. Gas6 Ϫ/Ϫ mice sensitized with MOG 35-55 peptide exhibit higher clinical scores during late peak to early chronic disease, with significantly increased SMI32 ϩ axonal swellings and Iba1 ϩ microglia/macrophages, enhanced expression of several proinflammatory mRNA molecules, and decreased expression of early oligodendrocyte maturation markers relative to WT mouse spinal cords with scores for 8 consecutive days. During acute EAE, flow cytometry showed significantly more macrophages but not T-cell infiltrates in Gas6 Ϫ/Ϫ spinal cords than WT spinal cords. Our data are consistent with GAS6 being protective during EAE by dampening the inflammatory response, thereby preserving axonal integrity and myelination.

Chagasic cardiomyopathy caused by Trypanosoma cruzi is a major health concern in Latin America and among immigrant populations in non-endemic areas. T. cruzi has a high affinity for host lipoproteins and uses the low density lipoprotein receptor (LDLr) for invasion. Herein, we report that T. cruzi infection is associated with an accumulation of LDL and cholesterol in tissues in both acute and chronic murine Chagas disease. Similar findings were observed in tissue samples from a human case of Chagasic cardiomyopathy. T. cruzi infection of cultured cells displayed increased invasion with increasing cholesterol levels in the medium. Studies of infected host cells demonstrated alterations in their cholesterol regulation. T. cruzi invasion/infection via LDLr appears to be involved in changes in intracellular cholesterol homeostasis. The observed changes in intracellular lipids and associated oxidative stress due to these elevated lipids may contribute to the development of Chagasic cardiomyopathy.

The continuing emergence of viral pathogens and their rapid spread into heavily populated areas around the world underscore the urgency for development of highly effective vaccines to generate protective antiviral Ab responses. Many established and newly emerging viral pathogens, including HIV and Ebola viruses, are most prevalent in regions of the world in which Mycobacterium tuberculosis infection remains endemic and vaccination at birth with M. bovis bacille Calmette–Guérin (BCG) is widely used. We have investigated the potential for using CD4+ T cells arising in response to BCG as a source of help for driving Ab responses against viral vaccines. To test this approach, we designed vaccines comprised of protein immunogens fused to an immunodominant CD4+ T cell epitope of the secreted Ag 85B protein of BCG. Proof-of-concept experiments showed that the presence of BCG-specific Th cells in previously BCG-vaccinated mice had a dose-sparing effect for subsequent vaccination with fusion proteins containing the Ag 85B epitope and consistently induced isotype switching to the IgG2c subclass. Studies using an Ebola virus glycoprotein fused to the Ag 85B epitope showed that prior BCG vaccination promoted high-affinity IgG1 responses that neutralized viral infection. The design of fusion protein vaccines with the ability to recruit BCG-specific CD4+ Th cells may be a useful and broadly applicable approach to generating improved vaccines against a range of established and newly emergent viral pathogens.

Analysis of antigen-specific CD4+ T cells in mycobacterial infections at the transcriptome level is informative but technically challenging. While several methods exist for identifying antigen-specific T cells, including intracellular cytokine staining, cell surface cytokine-capture assays, and staining with peptide:MHC-II multimers, all of these have significant technical constraints that limit their usefulness. Measurement of activation-induced expression of CD154 has been reported to detect live, antigen-specific CD4+ T cells but this approach remains underexplored, and to our knowledge has not previously been applied in mycobacteria-infected animals. Here we show that CD154 expression identifies adoptively transferred or endogenous antigen-specific CD4+ T cells induced by Mycobacterium bovis Bacillus Calmette-Guérin (BCG) vaccination. We confirmed that antigen-specific cytokine production was positively correlated with CD154 expression by CD4+ T cells from BCG-vaccinated mice, and show that high quality microarrays can be performed from RNA isolated from CD154+ cells purified by cell sorting. Analysis of microarray data demonstrated that the transcriptome of the CD4+ CD154+ cells was distinct from that of CD154− cells, and showed major enrichment of transcripts encoding multiple cytokines and pathways of cellular activation. One notable finding was the identification of a previously unrecognized subset of mycobacteria-specific CD4+ T cells characterized by the production of interleukin-3. Our results support the use of CD154 expression as a practical and reliable method to isolate live, antigen-specific CD4+ T cells for transcriptomic analysis and potentially for a range of other studies in infected or previously immunized hosts.

During Ag priming, naive CD4 + T cells differentiate into subsets with distinct patterns of cytokine expression that dictate to a major extent their functional roles in immune responses. We identified a subset of CD4 + T cells defined by secretion of IL-3 that was induced by Ag stimulation under conditions different from those associated with previously defined functional subsets. Using mouse models of bacterial and viral infections, we showed that IL-3-secreting CD4 + T cells were generated by infection at the skin and mucosa but not by infections introduced directly into the blood. Most IL-3-producing T cells coexpressed GM-CSF and other cytokines that define multifunctionality. Generation of IL-3-secreting T cells in vitro was dependent on IL-1 family cytokines and was inhibited by cytokines that induce canonical Th1 or Th2 cells. Our results identify IL-3-secreting CD4 + T cells as a potential functional subset that arises during priming of naive T cells in specific tissue locations. ImmunoHorizons, 2019, 3: 161-171.