A multi-organ map of the human immune system across age, sex and ethnicity

Understanding tissue biology's heterogeneity is crucial for advancing precision medicine. Despite the centrality of the immune system in tissue homeostasis, a detailed and comprehensive map of immune cell distribution and interactions across human tissues and demographics remains elusive. To fill this gap, we harmonised data from 12,981 single-cell RNA sequencing samples and curated 29 million cells from 45 anatomical sites to create a comprehensive compositional and transcriptional healthy map of the healthy immune system. We used this resource and a novel multilevel modelling approach to track immune ageing and test differences across sex and ethnicity. We uncovered conserved and tissue-specific immune-ageing programs, resolved sex-dependent differential ageing and identified ethnic diversity in clinically critical immune checkpoints. This study provides a quantitative baseline of the immune system, facilitating advances in precision medicine. By sharing our immune map, we hope to catalyse further breakthroughs in cancer, infectious disease, immunology and precision medicine.

CD26 (dipeptidyl-peptidase IV)-dependent recruitment of T cells in a rat asthma model

CD26 truncates several chemokines as well as neuropeptides and influences immune responses via modulation of cell adhesion and T cell activation, suggesting an involvement of CD26 in asthmatic and airway inflammation. Therefore, Fischer 344 (F344), Brown Norway (BN) and Lewis (LEW) rat strains, which differ in their CD26-like enzymatic activity, were compared using an asthma model. Additionally, two CD26-deficient mutant F344 rat substrains were included and compared to the wild-type F344 substrain. Immunization was performed twice with ovalbumin (OVA), and 2 weeks later the rats were challenged with OVA intratracheally Flow cytometry (FACS) analysis of different leucocyte subsets as well as enzyme-linked immunosorbent assay (ELISA) for IgE levels in the blood and bronchoalveolar lavage (BAL) were performed 24 h after challenge. LEW rats with the lowest CD26 activity among the rat strains investigated here displayed significantly reduced CD4+ T cell numbers in the BAL compared to wild-type F344 and BN rats. Moreover, in asthma, the ratio of CD26+ to CD26- T cell receptor (TCR)-positive cells increased significantly in F344 and LEW but not BN rats. Most intriguingly, in both CD26-deficient F344 rat substrains the number of CD4+ T lymphocytes was markedly reduced compared to wild-type F344. The decrease in T cell recruitment observed in the CD26-deficient rats was associated with significantly reduced OVA-specific IgE-titres. This is the first report to show a remarkably reduced T cell recruitment in rat strains that either lack or exhibit reduced CD26-like enzymatic activity, suggesting a role for CD26 in the pathogenesis of asthma via T cell-dependent processes such as antibody production.

Differential effects of neuropeptide Y (NPY) on leukocyte subsets in the blood: mobilization of B-1-like B-lymphocytes and activated monocytes

Sympathetic nervous system activation mobilizes leukocytes but it is unknown whether the concomitant neuropeptide Y (NPY)-release also alters blood leukocyte counts. Using chronic intravenous (i.v.) cannulation of freely moving rats and flow cytometry, time-, dose- and subset-specific effects of NPY on blood leukocytes were investigated 1-15 min after injection: High-dose NPY increases leukocytes numbers by preferentially mobilizing CD4(+) T-cells, activated NKR-P1A(+) monocytes and NK-cells. Low-dose NPY significantly decreases B-lymphocyte and NK-cell numbers. Furthermore, NPY dose-dependently mobilizes a previously undetected IgM(low)CD5(+)CD11b(+) B-cell subpopulation in rats ("B1-like" B-lymphocytes). These data suggest a role for the sympathetic neurotransmitter NPY in neuroimmune alterations in vivo.