Allergen-specific type 2 helper T (TH2) cells play a central role in initiating and orchestrating the allergic and asthmatic inflammatory response pathways. One major factor limiting the use of such atopic disease–causing T cells as both therapeutic targets and clinically useful biomarkers is the lack of an accepted methodology to identify and differentiate these cells from overall nonpathogenic TH2 cell types. We have described a subset of human memory TH2 cells confined to atopic individuals that includes all allergen-specific TH2 cells. These cells are terminally differentiated CD4+ T cells (CD27− and CD45RB−) characterized by coexpression of CRTH2, CD49d, and CD161 and exhibit numerous functional attributes distinct from conventional TH2 cells. Hence, we have denoted these cells with this stable allergic disease–related phenotype as the TH2A cell subset. Transcriptome analysis further revealed a distinct pathway in the initiation of pathogenic responses to allergen, and elimination of these cells is indicative of clinical responses induced by immunotherapy. Together, these findings identify a human TH2 cell signature in allergic diseases that could be used for response-monitoring and designing appropriate immunomodulatory strategies.
An important function of the blood–brain barrier is to exclude pathogens from the central nervous system, but some microorganisms benefit from the ability to enter this site. It has been proposed that Toxoplasma gondii can cross biological barriers as a motile extracellular form that uses transcellular or paracellular migration, or by infecting a host cell that then crosses the blood–brain barrier. Unexpectedly, analysis of acutely infected mice revealed significant numbers of free parasites in the blood and the presence of infected endothelial cells in the brain vasculature. The use of diverse transgenic parasites combined with reporter mice and intravital imaging demonstrated that replication in and lysis of endothelial cells precedes invasion of the central nervous system, and highlight a novel mechanism for parasite entry to the central nervous system.
Background
The main obstacle to elucidating the role of CD4+ T cells in allergen-specific immunotherapy has been the absence of an adequately sensitive approach to directly characterize rare allergen-specific T cells without introducing substantial phenotypic modifications by in vitro amplification.
Objective
To monitor in physiological conditions, the allergen-specific CD4+ T cells generated during natural pollen exposure and during allergy vaccine.
Methods
Alder pollen allergy was used as a model for studying seasonal allergies. Allergen-specific CD4+ T cells were tracked and characterized in twelve alder pollen-allergic, six non-allergic and nine allergy vaccine-treated individuals using peptide-MHC class II tetramers.
Results
Allergen-specific CD4+ T cells were detected in all of the alder pollen-allergic and non-allergic subjects tested. Pathogenic responses (CRTH2 expression and TH2-cytokine production) are specifically associated with terminally differentiated (CD27−) allergen-specific CD4+ T cells, which dominate in allergic individuals but are absent in non-allergic individuals. In contrast, CD27 expressing allergen-specific CD4+ T cells are present at low frequencies in both allergic and non-allergic individuals and reflect classical features of the protective immune response with high expression of IL-10 and IFN-γ. Restoration of a protective response during allergen-specific immunotherapy appears to be due to the preferential deletion of pathogenic (CD27−) allergen-specific CD4+ T cells accompanied by IL-10 induction in surviving CD27+ allergen-specific CD4+ T cells.
Conclusions
Differentiation stage divides allergen-specific CD4+ T cells into two distinct subpopulations with unique functional properties and different fates during allergen-specific immunotherapy.
The frequency of epitope specific naïve CD4+ T cells in humans has not been extensively examined. In this study, a systematic approach was used to examine the frequency of CD4+ T cells that recognize the Protective Antigen of Bacillus anthracis in both Anthrax Vaccine Adsorbed vaccinees and non-vaccinees with HLA-DRB1*01:01 haplotypes. Three epitopes were identified that had distinct degrees of immunodominance in subjects that had received the vaccine. Average naïve precursor frequencies of T cells specific for these different epitopes in the human repertoire ranged from 0.2 to 10 per million naïve CD4+ T cells, which is comparable to precursor frequencies observed in the murine repertoire. Frequencies of protective Antigen-specific T cells were two orders of magnitude higher in immunized subjects than in nonvaccinees. The frequencies of epitope specific memory CD4+ T cells in vaccinees were directly correlated with the frequencies of precursors in the naïve repertoire. At the level of TCR usage, at least one preferred Vβ in the naïve repertoire was present in the memory repertoire. These findings implicate naïve frequencies as a crucial factor in shaping the epitope specificity of memory CD4+ T cell responses.
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