Initial T cell activation is triggered by the formation of highly dynamic, spatiotemporally restricted Ca ²⁺ microdomains. Purinergic signaling is known to be involved in Ca ²⁺ influx in T cells at later stages compared to the initial microdomain formation. Using a high-resolution Ca ²⁺ live-cell imaging system, we show that the two purinergic cation channels P2X4 and P2X7 not only are involved in the global Ca ²⁺ signals but also promote initial Ca ²⁺ microdomains tens of milliseconds after T cell stimulation. These Ca ²⁺ microdomains were significantly decreased in T cells from P2rx4 ^−/− and P2rx7 ^−/− mice or by pharmacological inhibition or blocking. Furthermore, we show a pannexin-1–dependent activation of P2X4 in the absence of T cell receptor/CD3 stimulation. Subsequently, upon T cell receptor/CD3 stimulation, ATP release is increased and autocrine activation of both P2X4 and P2X7 then amplifies initial Ca ²⁺ microdomains already in the first second of T cell activation.

Due to their exceptional solubility and stability, nanobodies have emerged as powerful building blocks for research tools and therapeutics. However, their generation in llamas is cumbersome and costly. Here, by inserting an engineered llama immunoglobulin heavy chain (IgH) locus into IgH-deficient mice, we generate a transgenic mouse line, which we refer to as ‘LamaMouse’. We demonstrate that LamaMice solely express llama IgH molecules without association to Igκ or λ light chains. Immunization of LamaMice with AAV8, the receptor-binding domain of the SARS-CoV-2 spike protein, IgE, IgG2c, and CLEC9A enabled us to readily select respective target-specific nanobodies using classical hybridoma and phage display technologies, single B cell screening, and direct cloning of the nanobody-repertoire into a mammalian expression vector. Our work shows that the LamaMouse represents a flexible and broadly applicable platform for a facilitated selection of target-specific nanobodies.

Next to adrenergic signalling, purinergic pathways mediated by extracellular adenine nucleotides have been described to shape thermogenic and metabolic functions in brown adipose tissue (BAT). Here we describe high expression of P2X5 that is activated by ATP in mature adipocytes of BAT and differentiated brown adipocytes in vitro. The levels of other P2X family members were much lower, or expression was restricted to tissue-resident macrophages or endothelial cells. Global and brown adipocyte-specific P2rx5 deficiency resulted in lower expression of the uncoupling protein 1 (UCP1). However, indirect calorimetry studies showed that P2X5 did not affect systemic energy expenditure. Of note, glucose tolerance was impaired under chow and obesogenic high-fat diet conditions, which can be explained by lower glucose disposal into BAT but not into other organs. In summary, these data indicate a modulatory role of P2X5 in systemic and BAT-specific glucose metabolism.

Loss of brown adipose tissue (BAT) activity observed during ageing, obesity and living at thermoneutrality is associated with lipid accumulation, fibrosis and tissue inflammation in BAT. The mechanisms that promote this degenerative process of BAT remain largely enigmatic. Here, we show that an imbalance between sympathetic activation and mitochondrial energy handling causes BAT degeneration, which leads to impaired energy expenditure and systemic metabolic disturbances. Mechanistically, we demonstrate that brown adipocytes secrete ATP in response to imbalanced thermogenic activation, which activates P2X4 and P2X7 of BAT-resident macrophages. Notably, mice lacking activity of these purinergic receptors in myeloid cells are protected against BAT inflammation, thermogenic dysfunction and systemic metabolic disturbances under conditions of imbalanced BAT activation, thermoneutrality or overnutrition. These results highlight the relevance of extracellular ATP released by brown adipocytes as a paracrine signal for myeloid cells to initiate BAT degeneration.