Mattias N. E. Forsell

Atypical B-cells (ABCs) are observed across infections, yet their ontogeny and differentiation remain unclear. Using high-dimensional flow cytometry, single-cell transcriptomics, V(D)J sequencing, and functional assays in samples from individuals with malaria and healthy donors, we identify markers of cellular origin while tracking ABC differentiation. Early ABCs express CD11c and arise predominantly from memory B-cells. Two intermediate states originate from germinal center-derived and marginal zone-like B-cells. Pseudotime and lineage analyses reveal trajectories marked by progressive loss of CD24 and CD27, which is recapitulated in vitro, defining bona fide differentiation programs. Differentiation culminates in late ABCs lacking CD24, CD27, and CD21, while expressing CD11c, T-bet, and NKG7 at high levels, exhibiting partial overlap with double-negative-2 B-cells. Early and intermediate stages show greater plasma-cell differentiation potential and cytokine production capacity, whereas later stages acquire transcriptomic signatures of antigen presentation and association with microbial particles, defining stage-dependent functions that reconcile conflicting ABC roles. Comparable ABC populations occur in healthy blood and tonsils, with tissue-associated class switching and CD86 expression consistent with recent T-cell interaction. This framework consolidates ABC definitions along a single differentiation axis and clarifies their cellular origins.

Dementia is a neurodegenerative condition with multifactorial ethology, in which neurotropic herpes viruses have been proposed as potential contributors. While varicella-zoster virus (VZV) vaccination has been associated with reduced dementia risk, little is known about how longitudinal VZV-specific antibody dynamics relate to dementia onset. To investigate this, we analysed VZV-specific IgM and IgG levels in 2,867 samples from 1,612 older adults living in nursing homes. Capillary blood samples were collected at seven sampling periods between 2021 and 2024. Antibody levels were linked to national registry data. Linear mixed-effects models assessed (i) pre-diagnostic differences in antibody levels between individuals who subsequently developed dementia and those who did not, (ii) longitudinal trajectories relative to diagnosis, and (iii) within-individual changes among participants with samples before and after diagnosis. VZV-IgM levels were lower in participants who later developed dementia (estimate-0.075 log10, p = 0.037), with VZV-IgG showing a similar but nonsignificant trend. Longitudinal models demonstrated increasing VZV-specific antibody levels in the years surrounding dementia diagnosis, with significant yearly increases in IgM (0.0069 log10, p = 0.008) and a trend for elevated IgG. Within a subset of participants with samples on both sides of diagnosis (n = 23), VZV-IgM and VZV-IgG levels showed consistent within-individual increases, although statistical power was limited. These findings align with epidemiological evidence linking VZV vaccination to reduced dementia risk and provide new insight into potential immunological changes accompanying disease development. Further studies are warranted to clarify causal mechanisms and the role of antiviral or vaccination strategies in dementia prevention.

We evaluated the magnitude of antibody responses to seasonal influenza vaccination in people with HIV receiving ART compared with people without HIV. In a prospective cohort of 78 adults, influenza strain-specific IgG levels were measured up to one year after vaccination. Linear mixedeffects models were used to evaluate the longitudinal trends in antibody responses. IgG levels peaked two weeks post-vaccination and declined gradually over time in both groups. HIV status did not significantly influence antibody magnitude. These findings demonstrate that individuals with well-controlled HIV mount robust and durable humoral responses, supporting the effectiveness of annual influenza vaccination in this population.

Background: Older adults (> 65 years) residing in long-term care facilities (LTCFs) are at elevated risk of severe outcomes from respiratory infections. Infections often remain undetected or present atypically in this population, leading to underdiagnosis. Our study aimed to estimate the respiratory virus infection burden, independent of symptom presentation, among older adults in Swedish LTCFs in the post-pandemic period (2021–2024). Methods: We leveraged capillary blood samples and coupled national registry data from 1622 LTCF residents (median age = 87). A multiplex platform was used to quantify antigen-specific IgG and IgM responses to RSV (pre-/post-F, strain A-specific G-protein), influenza-A (H1N1 and H3N2 HA), influenza-B (HA) and SARS-CoV-2 (spike). Linear mixed-effects models were used to demonstrate the dynamics of antibody levels over time, adjusted for age, sex and comorbidities. Results: RSV-specific antibody responses peaked in spring 2022 ( p < 0.001), suggesting an impact of relaxed COVID-19-related restrictions on RSV exposure at LTCFs. RSV-specific antibodies subsequently declined over time until an increase during autumn 2023 ( p < 0.001). Geographic variation in pre-F antibody levels suggested localised RSV outbreaks. The total estimated RSV burden at LTCFs was markedly higher than official reports of the Swedish Public Health Agency. Influenza antibody dynamics reflected seasonal trends and were strongly influenced by annual vaccination. A random forest classifier incorporating serological profiles with demographics, location and comorbidities significantly outperformed a model without serological data (AUC-ROC = 0.67 vs. 0.58), although discriminatory performance remained modest. Higher levels of RSV pre-F antibodies in autumn 2021 were associated with increased one-year mortality in logistic regression (OR = 1.43, p = 0.024). Exploratory survival analysis indicated a trend that elevated levels of RSV pre-F antibodies during low population immunity may confer a transiently elevated early hazard of death, although this did not reach statistical significance (HR = 4.50, p = 0.087). Conclusions: We observed substantial respiratory virus circulation among older adults in Swedish LTCFs and show that RSV burden is under-reported. The results highlight a need for further research into the role of RSV pre-F antibody levels in preventing severe outcomes, potentially via vaccination of LTCF residents. Our scalable serological surveillance system is a valuable approach to detect respiratory infections in LTCFs, independent of symptom presentation or healthcare-seeking behaviour.

CD4+ T cells are components of the adaptive immune system with a plethora of subtype-specific functions. In order to further dissect the activation and differentiation regulatory program(s) of individual CD4+ T cell subsets, we performed an in vitro activation and differentiation of human primary naive CD4+ T cells towards Th1, Th2, Th17 and Treg subtypes followed by the single-cell RNA-seq and ATAC-seq (multiome) analysis. Resulting multiome data were used for constructing the subtype-specific gene regulatory networks, which were next assessed for their differences/similarities among the subtypes. Surprisingly, a conserved set of 8 "backbone" transcription factors (TFs) was identified as highly central in all subtypes, however, with unique differentiation-driven rewiring tendency. Subtype-specific "driver" TFs were identified in the case of Th1-Th1_17-Th17 lineage (EOMES, HLF), naive Tregs (ESR1, DACH1), and memory Tregs (SOX13). Finally, we applied community detection algorithms to identify potential non-obvious groups of genes that regulate diverse molecular functions within the differentiated subtypes, linked to the backbone TFs. Our atlas aims at providing a high resolution understanding of the gene regulatory networks and their rewiring in human primary CD4+ T cells, upon activation and differentiation.

Top 30 markers of clusters in CAF subset of single cell data

Lists of genes used to calculate signature scores for cytolytic activity, T cell activation and M1 vs M2 macrophage polarization in single cell data analysis

Orthotopic transplantation of gal 4–KO cell lines identifies differences in CD4+ and CD8+ cell infiltration and function. A, Schematic of the orthotopic transplantation experiments using gal 4–KO and R26 control cell lines transplanted into immune competent C57BL6/J mice. B, Representative IHC images of gal 4 in R26 control and gal 4–KO tumors (top scale bar, 50 μm; bottom, scale bar, 20 μm). A total of 10 tumors were stained, 5 of each condition. C–E, Representative IHC images (left) and quantification (right) of CD4+ cells (P = 0.0032; C), CD8+ cells (P = <0.0001; D), and FOXP3+ cells (ns., no significant difference; E), in orthotopically transplanted tumors with gal 4 (R26 controls) and no gal 4 expression (Gal 4–KO); scale bar, 100 μm. Significance calculated using the Mann–Whitney test. Error bars show mean ± SEM. F, Representative contour plots illustrating gating strategies of intratumoral CD8+ T cells (left). Scatter plot with bar graph showing the fraction of CD8+ cells out of the total amount of CD45+ CD3+ cells in R26 control and gal 4–KO tumors (right; P = 0.0001). Significance calculated using the Mann–Whitney test. Error bars show mean±SEM. G Representative contour plots of intratumoral CD45+, CD3+, CD8+ cells (CD8+ T cells gated as in Fig. 3 F) expressing the exhaustion markers PD-1 (x-axis) and Tim-3 (y-axis) in R26 control and gal 4–KO tumors (left). Scatter plot with bar graph s (right) showing quantification of CD8+ T cells exhaustion (PD1+ and Tim-3 cells in Q2) in R26 control and gal 4–KO tumors (P = 0.046). Significance calculated using the Mann–Whitney test. Error bars show mean with SEM. **, P < 0.01; ***, P < 0.001.

Top 30 markers of clusters in Immune subset of single cell data