Environmental DNA, or eDNA, metabarcoding has transformed biodiversity monitoring over the past decade. Instead of catching and killing insects to identify them, scientists can now collect traces of genetic material that organisms shed in their environment and identify the species from those fragments. In pollinator research, the pioneering work of Thomsen and Sigsgaard in 2019 showed that flowers themselves can serve as a source of arthropod eDNA, allowing researchers to reconstruct pollination networks non-invasively. Since then, a growing number of studies have confirmed that eDNA collected from flowers can effectively reveal insect-plant interactions with high sensitivity, taxonomic breadth, and temporal resolution.

However, the method has faced persistent technical obstacles. One major problem is that flowers are not only visited by pollinators; they are also home to small insects such as thrips, aphids, and pollen beetles that may live on the flower and enter the sample as whole individuals. These flower-living organisms contribute orders of magnitude more DNA than the trace material left by transient pollinators. Because the polymerase chain reaction, or PCR, preferentially amplifies the most abundant DNA in a sample, the genetic signal of bees can be outcompeted by the overwhelming DNA of these abundant residents, producing false negatives. A second challenge lies in the universal arthropod primers themselves, which exhibit well-documented amplification bias toward certain taxonomic groups and often underrepresent bees in mixed floral community samples.

These biases are especially problematic for studies aiming to reconstruct plant-pollinator networks, because such inference requires extensive within-group taxonomic coverage rather than a focus on the most common arthropod taxa in general. The role of certain bee species may be underestimated, skewing network structure and leading to misleading conclusions for biodiversity assessments and conservation efforts. Despite bees being one of the most ecologically and economically important groups in pollination networks, no bee-specific metabarcoding primer had been available until now.

To close this gap, the research team targeted the mitochondrial cytochrome c oxidase subunit I gene, or COI, the most widely used DNA barcode for the animal kingdom. COI combines conserved primer-binding sites with sufficient sequence variation to discriminate between species, and it is well represented in public sequence databases such as BOLD and NCBI. BOLD currently contains approximately 112,000 publicly available bee sequences, of which roughly 108,000 correspond to the standard COI barcode region. The researchers downloaded COI sequences from flower-visiting arthropod families previously detected in flower wash samples, aligned them, and removed low-quality or suspect records, yielding a reference set representing 173,830 unique arthropod species, of which 2,394 were bees covering 39 percent of Austrian bee diversity.

From this alignment, the team identified conserved regions unique within bees, paying particular attention to avoiding shared consensus with non-target groups such as thrips and pollen beetles, which had previously dominated PCR output from flower wash samples. Using manual expert judgment alongside established primer design principles, they generated two forward and three reverse primer candidates with lengths of 20 to 30 base pairs, melting temperatures of 50 to 60 degrees Celsius, and expected amplicon sizes of roughly 200 to 400 base pairs. Degenerate bases were incorporated to account for sequence variation among bee taxa, and all candidates were checked for secondary structures such as hairpins and dimers. The selected pair, BeePrimeF and BeePrimeR, amplifies a short COI fragment of 198 base pairs, a length suitable for species-level resolution in most organismal groups and compatible with Illumina sequencing platforms.

Validation proceeded in two stages. In silico, the primers were screened against an alignment of 67,352 centroid sequences clustered from a total of 316,254 sequences retrieved from NCBI, using the R package PrimerMiner to calculate weighted penalty scores that account for mismatch position and type. Both primers showed high binding complementarity to bee sequences, while their affinity to non-target arthropod groups was substantially lower, with mismatches concentrated at the critical 3-prime ends where they strongly reduce amplification efficiency. In vitro, the primers were tested against DNA extracts from 48 bee specimens representing 38 species and 23 genera spanning all six bee families of Central Europe, alongside 34 non-target extracts including spiders, thrips, beetles, flies, bugs, butterflies, wasps, and ants. Thirty-three of the 38 bee extracts were successfully amplified, an 86.84 percent success rate, while only nine of the 34 non-target extracts yielded positive results, indicating a non-target exclusion rate of approximately 73.52 percent. Notably, no amplification occurred in groups known to be problematic in flower metabarcoding, such as thrips, pollen beetles, or aphids.

The decisive test came with field samples. The researchers applied BeePrime to eDNA extracted from 48 flower-wash samples collected in Austrian flower strips in 2024 and compared the results directly with the universal arthropod primer pair fwhF2/fwhR2n, one of the most widely recognized primers available. BeePrime detected bee DNA in 35 of the 48 samples, compared with only 17 for the universal primer, raising per-sample detection from 35.4 percent to 72.9 percent. At the species level, the universal primer identified 14 bee-positive samples, while BeePrime detected 87, a sixfold increase. Individual floral samples typically yielded multiple bee species rather than single detections, with a mean of 1.8 species-level detections per sample and a maximum of 6. Across the entire dataset, the universal primer recovered just six distinct bee species, whereas BeePrime detected 27.

The improvement in sequencing efficiency was equally striking. Amplifications with the universal primer produced only very low proportions of bee reads, with a median of 0.03 percent, in many cases approaching zero. BeePrime yielded a median of 15 percent and a mean of approximately 30 percent bee reads per sample, a difference confirmed as highly significant by a Wilcoxon rank-sum test. Thrips, which dominated the genus-level dataset with almost 85 percent of all reads under the universal primer, were reduced to roughly 30 percent under BeePrime, while wild bees rose from only a few percent to nearly 50 percent of reads. Together with honeybees, bees represented more than 60 percent of the total relative read proportion with the new primer pair.

Every bee taxon detected with BeePrime had previously been recorded at the same sites using traditional hand-net sampling and morphological identification, corroborating the molecular assignments. The authors caution, however, that empirical performance has so far been demonstrated only for common bee taxa in Central European agricultural landscapes, and that local testing is advised before applying the primer pair in other biogeographic regions. Several Apidae species, including some carpenter bees and long-horned bees, did not amplify successfully despite acceptable primer fit, so underdetected lineages should not automatically be interpreted as absent in ecological network analyses. The researchers also emphasize that read numbers do not translate directly into bee abundance, since DNA deposition depends on body size, body hairiness, and behavior. Nevertheless, by overcoming a key methodological bottleneck in pollinator eDNA metabarcoding, BeePrime substantially strengthens the molecular toolkit available for monitoring bee diversity and resolving plant-pollinator networks, marking a major step toward establishing floral eDNA as a routine approach in ecological monitoring and conservation.

Subject of Research: Development and validation of a bee-specific COI metabarcoding primer pair for non-invasive monitoring of plant-pollinator interactions

Article Title: A bee-specific metabarcoding primer pair for non-invasive assessments of plant–pollinator interactions

Article References: Gurten, S., Sint, D., Traugott, M., & Rennstam Rubbmark, O. R. (2026). A bee-specific metabarcoding primer pair for non-invasive assessments of plant–pollinator interactions. Metabarcoding and Metagenomics, 10, Article e183708. https://doi.org/10.3897/mbmg.10.183708

Image Credits: AI Generated

DOI: 10.3897/mbmg.10.183708

Keywords: bees, environmental DNA, metabarcoding, pollinators, primer design, COI barcode, plant-pollinator networks, biodiversity monitoring, bee-specific, primer, pair, non-invasive

The structures in question are known as artery tertiary lymphoid organs, or ATLOs. Unlike the classical lymph nodes and spleen, which develop during embryogenesis and serve the entire body, tertiary lymphoid organs arise postnatally in response to chronic inflammation at affected tissues. In atherosclerosis, they form in the adventitia, the outermost layer of the arterial wall, adjacent to plaques rich in immune cells. Previous work had established that these structures contain germinal centers, the specialized microenvironments where B cells proliferate, mutate their antibody genes, and undergo selection for increasingly potent antigen binding. What remained unknown was what these germinal centers were actually targeting, and whether the antibodies they produced mattered for disease.

To answer those questions, the research team, led by Zihao Zhang, Yue Zhang, Shu Ran, Ying Wang and colleagues, combined single-cell transcriptomic profiling with B cell receptor sequencing of germinal center B cells harvested from artery tertiary lymphoid organs. Single-cell transcriptomics allows researchers to capture the complete gene expression program of individual cells, revealing their identity, activation state, and developmental trajectory. B cell receptor sequencing, meanwhile, reads out the rearranged antibody genes carried by each B cell, providing a molecular fingerprint of the antigen-binding receptor that defines the cell’s specificity. By layering these two datasets on top of one another, the investigators could reconstruct, at unprecedented resolution, the population of B cells being educated within the arterial wall itself.

The analysis revealed a clonally expanded population of autoreactive B cells within the ATLO germinal centers, indicating that these cells had undergone the canonical process of somatic hypermutation and antigen-driven selection that normally refines antibody responses during infection or vaccination. From this population, the team cloned a monoclonal antibody, designated A6, and demonstrated that it binds with high affinity to histone 2B, or H2B, one of the core histone proteins around which DNA is wrapped in every cell nucleus. Histones are potent immunological stimuli, well known to activate innate immune pathways, but the identification of a germinal center-derived, high-affinity antibody specific for H2B within the artery wall was unexpected and mechanistically significant.

The pathogenic relevance of the finding was established through two complementary lines of experimentation. First, the researchers tested H2B vaccination: when animals were immunized with histone 2B, the resulting immune response markedly accelerated the progression of atherosclerosis, confirming that a targeted anti-H2B response is sufficient to worsen disease. Second, and more directly, the team performed adoptive transfer of the anti-H2B A6 monoclonal antibody itself. Simply delivering the purified antibody into circulation was enough to significantly speed plaque development, demonstrating that the antibody is not merely a marker of the disease process but an active driver of it.

These results carry substantial mechanistic weight because they close a causal loop. Earlier studies had documented that tertiary lymphoid organs appear in the arterial adventitia as atherosclerosis advances, and that their germinal centers become more prominent with disease severity. But correlation is not causation, and it remained possible that the local immune structures were protective, attempting to contain plaque inflammation, or merely incidental. By identifying a specific autoantibody-autoantigen pair encoded within these structures and showing that the antibody accelerates disease when transferred, the study establishes that ATLOs are not passive observers but productive factories of pathogenic humoral immunity.

The technical achievement underlying the discovery deserves emphasis. Germinal center B cells are notoriously difficult to study because they are short-lived, rapidly dividing, and spatially restricted within organized lymphoid tissue. Extracting them from the arterial wall, dissociating the tissue into single cells while preserving RNA quality, and obtaining paired heavy- and light-chain B cell receptor sequences from each cell requires meticulous single-cell handling. The successful cloning of a functional monoclonal antibody from this dataset, one that retains its specificity and pathogenic activity when expressed recombinantly, validates the entire pipeline and opens the door to systematically cataloging the full repertoire of antigens targeted within atherosclerotic ATLOs.

The identification of H2B as the target antigen also connects atherosclerosis to a broader theme in autoimmunity. Anti-histone antibodies are hallmarks of several systemic autoimmune diseases, most notably drug-induced lupus, where they bind nuclear components released by dying cells. In atherosclerotic plaques, cell death is abundant: foam cells undergo apoptosis, necrotic cores accumulate, and nuclear debris is released into the plaque microenvironment. It is plausible that this ongoing cell death provides a continuous supply of histone antigen, which drains to the adjacent adventitial lymphoid structures and drives the affinity maturation of autoreactive B cells. The new findings suggest that atherosclerosis may therefore share fundamental immunological machinery with classical autoimmune diseases, a concept that reframes how the field thinks about cardiovascular inflammation.

Therapeutically, the work suggests several possible avenues, though the researchers are careful to note that translation from experimental models to human patients will require further validation. If comparable anti-H2B responses are confirmed in human atherosclerotic arteries, the autoantibody could serve as a biomarker for identifying patients whose disease is driven by autoreactive immunity. More ambitiously, the pathways that organize and sustain artery tertiary lymphoid organs, including the lymphotoxin and chemokine networks that recruit and retain lymphocytes in the vessel wall, could become targets for interventions designed to quiet local antibody production without globally suppressing protective immunity. Given that atherosclerosis remains the leading cause of death worldwide despite aggressive lipid-lowering therapy, any mechanism that explains residual cardiovascular risk in patients is of enormous clinical interest.

The study also raises fundamental questions about how immune tolerance breaks down inside the artery. Germinal centers normally enforce stringent selection against self-reactive B cells, yet the ATLO germinal centers clearly nurtured a high-affinity autoreactive clone to maturity. Understanding why the arterial environment licenses this breach, whether through the character of the antigens presented, the cytokine milieu, or the absence of regulatory cell networks found in conventional lymphoid tissue, may reveal general principles applicable to other chronic inflammatory diseases in which tertiary lymphoid structures arise, from rheumatoid arthritis to organ transplant rejection. For now, the demonstration that a single cloned antibody targeting a nuclear protein can measurably accelerate the arterial disease that kills more people than any other stands as a vivid reminder that the immune system, in the wrong context, can be as dangerous as any traditional risk factor.

The adventitia, where these lymphoid structures take root, has long been treated as a largely passive scaffold of collagen, vasa vasorum, and resident fibroblasts. The demonstration that it can host affinity-matured humoral responses repositions this outer arterial layer as an immunologically active compartment. It also helps explain earlier observations that immune-cell clusters in the adventitia expand in parallel with plaque burden and that lymphatic vessels draining the arterial wall become more prominent as disease advances, providing a plausible route by which plaque-derived antigens reach the local immune structures.

Histone 2B belongs to a family of proteins that are normally sequestered inside the nucleus, where they package DNA into nucleosomes. When cells die, particularly through the inflammatory forms of cell death common in plaques, histones can escape into the extracellular space, where they act as damage-associated molecular patterns that stimulate innate receptors. The new work shows that this same nuclear material can also serve as a target for affinity-matured adaptive responses, linking innate danger signaling and autoreactive antibody production within a single tissue site.

The adoptive transfer result is especially informative, because it separates the antibody itself from the cells that produce it. Accelerated plaque development following antibody delivery alone indicates that circulating anti-H2B immunoglobulin is sufficient to promote disease, pointing future mechanistic studies toward how the antibody engages antigens within the vessel wall and what effector pathways it recruits once bound.

Subject of Research: Artery tertiary lymphoid organs encode a pathogenic high-affinity autoantibody−autoantigen pair in atherosclerosis

Article Title: Artery tertiary lymphoid organs encode a pathogenic high-affinity autoantibody−autoantigen pair in atherosclerosis

Article References: Zhang, C., Zhang, X., Ran, Y., Wang, Z., Li, L., Wang, S., Zheng, J., Zhang, Y., Sun, T., Li, Y., Lu, S., Hong, M., Ma, Z., Steffens, S., Hristov, M., Blanchet, X., Zhu, J., Dou, X., Deng, X., … Yin, C. (2026). Artery tertiary lymphoid organs encode a pathogenic high-affinity autoantibody−autoantigen pair in atherosclerosis. Nature Cardiovascular Research, 5(9), 869-890. https://doi.org/10.1038/s44161-026-00864-w

Image Credits: AI Generated

DOI: 10.1038/s44161-026-00864-w

Keywords: Artery, tertiary, lymphoid, organs, encode, pathogenic, high-affinity, autoantibody, autoantigen, pair, atherosclerosis, scientific research