The kinase LCK and CD4/CD8 co-receptors are crucial components of the T cell antigen receptor (TCR) signaling machinery, leading to key T cell fate decisions. Despite decades of research, the roles of CD4-LCK and CD8-LCK interactions in TCR triggering in vivo remain unknown. In this study, we created animal models expressing endogenous levels of modified LCK to resolve whether and how co-receptor-bound LCK drives TCR signaling. We demonstrated that the role of LCK depends on the co-receptor to which it is bound. The CD8-bound LCK is largely dispensable for antiviral and antitumor activity of cytotoxic T cells in mice; however, it facilitates CD8+ T cell responses to suboptimal antigens in a kinase-dependent manner. By contrast, the CD4-bound LCK is required for efficient development and function of helper T cells via a kinase-independent stabilization of surface CD4. Overall, our findings reveal the role of co-receptor-bound LCK in T cell biology, show that CD4- and CD8-bound LCK drive T cell development and effector immune responses using qualitatively different mechanisms and identify the co-receptor-LCK interactions as promising targets for immunomodulation.

• MeSH
• CD4 Antigens MeSH
• CD8 Antigens metabolism   MeSH
• T-Lymphocytes, Cytotoxic * metabolism   MeSH
• Mice MeSH
• Receptors, Antigen, T-Cell metabolism   MeSH
• Signal Transduction MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) * metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• CD4 Antigens MeSH
• CD8 Antigens MeSH
• Receptors, Antigen, T-Cell MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) * MeSH

Mature T cells are selected for recognizing self-antigens with low to intermediate affinity in the thymus. Recently, the relative differences in self-reactivity among individual T-cell clones were appreciated as important factors regulating their fate and immune response, but the role of self-reactivity in T-cell biology is incompletely understood. We addressed the role of self-reactivity in T-cell diversity by generating an atlas of mouse peripheral CD8+ T cells, which revealed two unconventional populations of antigen-inexperienced T cells. In the next step, we examined the steady-state phenotype of monoclonal T cells with various levels of self-reactivity. Highly self-reactive clones preferentially differentiate into antigen-inexperienced memory-like cells, but do not form a population expressing type I interferon-induced genes, showing that these two subsets have unrelated origins. The functional comparison of naïve monoclonal CD8+ T cells specific to the identical model antigen did not show any correlation between the level of self-reactivity and the magnitude of the immune response.

• Keywords
• T cell, T-cell diversity, antigen-inexperienced memory-like CD8 T cells, interferon response, self-reactivity,
• MeSH
• Autoantigens MeSH
• Clone Cells MeSH
• CD8-Positive T-Lymphocytes * MeSH
• Interferon Type I * MeSH
• Mice MeSH
• Thymus Gland MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Autoantigens MeSH
• Interferon Type I * MeSH

Ag-inexperienced memory-like T (AIMT) cells are functionally unique T cells, representing one of the two largest subsets of murine CD8+ T cells. However, differences between laboratory inbred strains, insufficient data from germ-free mice, a complete lack of data from feral mice, and an unclear relationship between AIMT cells formation during aging represent major barriers for better understanding of their biology. We performed a thorough characterization of AIMT cells from mice of different genetic background, age, and hygienic status by flow cytometry and multiomics approaches, including analyses of gene expression, TCR repertoire, and microbial colonization. Our data showed that AIMT cells are steadily present in mice, independent of their genetic background and hygienic status. Despite differences in their gene expression profiles, young and aged AIMT cells originate from identical clones. We identified that CD122 discriminates two major subsets of AIMT cells in a strain-independent manner. Whereas thymic CD122LOW AIMT cells (innate memory) prevail only in young animals with high thymic IL-4 production, peripheral CD122HIGH AIMT cells (virtual memory) dominate in aged mice. Cohousing with feral mice changed the bacterial colonization of laboratory strains but had only minimal effects on the CD8+ T cell compartment, including AIMT cells.

• MeSH
• Antigens genetics   immunology   MeSH
• Phenotype MeSH
• Immunologic Memory genetics   immunology   MeSH
• Clonal Evolution MeSH
• Mice, Inbred BALB C MeSH
• Mice, Inbred C57BL MeSH
• Mice, Transgenic MeSH
• Mice MeSH
• Genomic Instability MeSH
• Aging genetics   immunology   MeSH
• T-Lymphocytes immunology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens MeSH

Bardet-Biedl Syndrome (BBS) is a pleiotropic genetic disease caused by the dysfunction of primary cilia. The immune system of patients with ciliopathies has not been investigated. However, there are multiple indications that the impairment of the processes typically associated with cilia may have influence on the hematopoietic compartment and immunity. In this study, we analyze clinical data of BBS patients and corresponding mouse models carrying mutations in Bbs4 or Bbs18. We find that BBS patients have a higher prevalence of certain autoimmune diseases. Both BBS patients and animal models have altered red blood cell and platelet compartments, as well as elevated white blood cell levels. Some of the hematopoietic system alterations are associated with BBS-induced obesity. Moreover, we observe that the development and homeostasis of B cells in mice is regulated by the transport complex BBSome, whose dysfunction is a common cause of BBS. The BBSome limits canonical WNT signaling and increases CXCL12 levels in bone marrow stromal cells. Taken together, our study reveals a connection between a ciliopathy and dysregulated immune and hematopoietic systems.

• Keywords
• Bardet-Biedl Syndrome, CXCL12, ciliopathy, immunity, obesity,
• MeSH
• Autoimmune Diseases * MeSH
• Bardet-Biedl Syndrome * complications   genetics   MeSH
• Cilia MeSH
• Hematopoiesis * genetics   MeSH
• Humans MeSH
• Disease Models, Animal MeSH
• Mutation MeSH
• Mice MeSH
• Microtubule-Associated Proteins genetics   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• BBS4 protein, mouse MeSH Browser
• Microtubule-Associated Proteins MeSH

The development of thymic regulatory T cells (Treg) is mediated by Aire-regulated self-antigen presentation on medullary thymic epithelial cells (mTECs) and dendritic cells (DCs), but the cooperation between these cells is still poorly understood. Here we show that signaling through Toll-like receptors (TLR) expressed on mTECs regulates the production of specific chemokines and other genes associated with post-Aire mTEC development. Using single-cell RNA-sequencing, we identify a new thymic CD14+Sirpα+ population of monocyte-derived dendritic cells (CD14+moDC) that are enriched in the thymic medulla and effectively acquire mTEC-derived antigens in response to the above chemokines. Consistently, the cellularity of CD14+moDC is diminished in mice with MyD88-deficient TECs, in which the frequency and functionality of thymic CD25+Foxp3+ Tregs are decreased, leading to aggravated mouse experimental colitis. Thus, our findings describe a TLR-dependent function of mTECs for the recruitment of CD14+moDC, the generation of Tregs, and thereby the establishment of central tolerance.

• MeSH
• Single-Cell Analysis MeSH
• Autoantigens immunology   MeSH
• Self Tolerance MeSH
• Chemokines immunology   metabolism   MeSH
• Dendritic Cells immunology   MeSH
• Epithelial Cells immunology   metabolism   MeSH
• Colitis immunology   MeSH
• Lipopolysaccharide Receptors metabolism   MeSH
• Disease Models, Animal MeSH
• Mice MeSH
• Adoptive Transfer MeSH
• Antigen Presentation MeSH
• Flow Cytometry MeSH
• Receptors, Immunologic metabolism   MeSH
• T-Lymphocytes, Regulatory immunology   transplantation   MeSH
• Sequence Analysis, RNA MeSH
• Cell Separation MeSH
• Signal Transduction immunology   MeSH
• Thymus Gland cytology   immunology   MeSH
• Toll-Like Receptors metabolism   MeSH
• Up-Regulation MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Autoantigens MeSH
• Cd14 protein, mouse MeSH Browser
• Chemokines MeSH
• Lipopolysaccharide Receptors MeSH
• Receptors, Immunologic MeSH
• Sirpa protein, mouse MeSH Browser
• Toll-Like Receptors MeSH

Overtly self-reactive T cells are removed during thymic selection. However, it has been recently established that T cell self-reactivity promotes protective immune responses. Apparently, the level of self-reactivity of mature T cells must be tightly balanced. Our mathematical model and experimental data show that the dynamic regulation of CD4- and CD8-LCK coupling establish the self-reactivity of the peripheral T cell pool. The stoichiometry of the interaction between CD8 and LCK, but not between CD4 and LCK, substantially increases upon T cell maturation. As a result, peripheral CD8+ T cells are more self-reactive than CD4+ T cells. The different levels of self-reactivity of mature CD8+ and CD4+ T cells likely reflect the unique roles of these subsets in immunity. These results indicate that the evolutionary selection pressure tuned the CD4-LCK and CD8-LCK stoichiometries, as they represent the unique parts of the proximal T cell receptor (TCR) signaling pathway, which differ between CD4+ and CD8+ T cells.

• Keywords
• CD4, CD8, LCK, T cell, TCR, evolution of the immune system, lymphocyte, self-reactivity, signaling, thymus,
• MeSH
• Antigens metabolism   MeSH
• Cell Differentiation MeSH
• CD4-Positive T-Lymphocytes cytology   metabolism   MeSH
• CD8-Positive T-Lymphocytes cytology   metabolism   MeSH
• Homeostasis MeSH
• Mice, Inbred C57BL MeSH
• Signal Transduction MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens MeSH
• Lymphocyte Specific Protein Tyrosine Kinase p56(lck) MeSH