Plasma membrane order maps functional diversity in immune cells

The concept of membrane order provides a quantitative framework for describing a property of the plasma membrane that has historically been discussed in qualitative terms. Rather than asking simply whether a region of membrane is more or less fluid, researchers can now assign numerical values that reflect the degree of conformational ordering of lipid acyl chains at a given location and moment. This shift from categorical to continuous measurement matters because the plasma membrane is not a uniform barrier but a mosaic of microenvironments whose physical properties influence how embedded proteins behave. Receptors, ion channels, and signaling enzymes all respond to the packing density and viscosity of their immediate lipid surroundings, so a map of membrane order is, in effect, a proxy map of where signaling competence is concentrated across the cell surface.

Immune cells are particularly instructive subjects for this kind of analysis because their function depends on rapid, spatially organized surface events. A T cell encountering an antigen-presenting cell reorganizes its membrane within minutes, clustering receptors and adaptor proteins into a structured interface known as the immunological synapse. B cells undergo analogous rearrangements when their B cell receptor binds antigen. Natural killer cells survey target cells and form activating or inhibitory contacts whose outcomes depend on the balance of receptor signals at the contact site. In each case, the physical state of the membrane at the interface is not incidental; it determines which proteins can diffuse into or out of the contact zone, which lipid species segregate there, and how efficiently the cytoskeleton can be remodeled to stabilize or dissolve the interaction.

The biophysical basis of membrane order lies in the composition and behavior of the lipid bilayer itself. Sphingolipids and phospholipids with saturated acyl chains pack tightly and adopt extended conformations, producing regions of high order. Unsaturated phospholipids, with kinks introduced by double bonds, disrupt packing and lower local order. Cholesterol intercalates between phospholipids and has a concentration-dependent effect: at moderate levels it rigidifies fluid bilayers and promotes the coalescence of ordered domains, while at high levels it can increase order further in saturated lipid environments. These interactions underlie the long-standing hypothesis of lipid rafts, nanoscale assemblies enriched in sphingolipids, cholesterol, and certain lipid-anchored proteins that have been proposed to serve as platforms for signaling. Direct visualization of rafts in living cells proved technically elusive for decades because the domains are small, transient, and below the diffraction limit of conventional microscopy, which fueled considerable debate about their physiological relevance.

Probe-based imaging has been central to resolving this debate. Environmentally sensitive dyes such as laurdan and its derivatives report on the hydration and packing of their lipid surroundings through shifts in their emission spectra, allowing order to be quantified as a generalized polarization value. When such probes are targeted to specific leaflets of the plasma membrane or conjugated to molecules that partition preferentially into ordered or disordered phases, they provide spatially resolved readouts of membrane physics in live cells. The interpretation of these measurements requires care, because probe partitioning can itself perturb the membrane, and spectral readouts can be confounded by factors such as pH, probe concentration, and photobleaching. Advances in probe chemistry, calibration standards, and imaging modalities have progressively addressed these concerns, making it possible to compare order measurements across cell types and experimental conditions with increasing confidence.

Super-resolution microscopy techniques have further transformed the field by bringing the relevant length scales within reach. Stimulated emission depletion microscopy, photoactivated localization microscopy, and stochastic optical reconstruction microscopy each achieve effective resolutions well below the diffraction limit, revealing that proteins and lipids once thought to be uniformly distributed actually occupy discrete nanoscale clusters. Combining these structural methods with spectral imaging of order-sensitive probes allows researchers to ask whether regions of high membrane order coincide with clusters of signaling proteins, and whether such coincidence changes upon receptor activation. In immune cells, this combination has shown that ordered domains accumulate at sites of receptor engagement and that disrupting ordered lipid phases, for example by depleting cholesterol or inhibiting sphingolipid synthesis, impairs signaling outputs such as calcium flux, phosphorylation cascades, and cytokine production.

The relationship between membrane order and the actin cytoskeleton adds another layer of regulatory complexity. Cortical actin filaments exert forces on the overlying membrane, creating regions of tension and constriction that can influence lipid phase behavior. Actin-driven structures such as membrane ruffles, microvilli, and picket-and-fence arrangements compartmentalize lateral diffusion, effectively corralling proteins and lipids into transient domains. Conversely, the lipid composition of the membrane affects how actin-binding proteins attach to the cytoplasmic face, creating a bidirectional feedback loop. In migrating immune cells, leading-edge membranes enriched in unsaturated lipids and low order support the protrusive activity needed for chemotaxis, while the uropod exhibits different physical properties that promote adhesion and retraction. Mapping order across a polarized cell therefore reveals how physical heterogeneity aligns with functional polarity.

Pathogens have evolved to exploit membrane physical properties during infection, which underscores the selective pressures shaping these systems. Enveloped viruses bud from membranes whose lipid composition facilitates assembly and release, and some viruses preferentially incorporate ordered lipid domains into their envelopes. Bacterial toxins that bind cholesterol or sphingomyelin use ordered domains as points of attachment for pore formation. Intracellular pathogens manipulate host membrane traffic and lipid metabolism to create replication niches with altered physical properties. In each scenario, the immune response must contend with a membrane environment that the pathogen has actively reshaped, and measurements of membrane order in infected cells can reveal these manipulations as measurable shifts in surface biophysics.

Aging and metabolic state also leave imprints on membrane order. Dietary lipid composition influences the saturation profile of membrane phospholipids over time, and age-associated changes in lipid metabolism have been documented in immune cells from multiple organisms. Membranes from aged T cells, for example, show altered cholesterol content and modified order characteristics that correlate with diminished signaling capacity upon antigen stimulation. Metabolic diseases such as obesity and diabetes, which alter circulating lipid profiles, produce measurable changes in the membrane properties of circulating leukocytes. These observations suggest that membrane order could serve as an integrative readout of an organism’s metabolic and inflammatory history, encoded in the physical state of its immune cell surfaces.

Therapeutically, the sensitivity of membrane order to lipid metabolism opens avenues for intervention. Statins, which reduce cholesterol synthesis, have immunomodulatory effects that may partly reflect changes in membrane organization. Drugs targeting sphingolipid metabolism, such as inhibitors of sphingomyelin synthase or glucosylceramide synthase, alter ordered domain abundance and have shown effects on inflammatory signaling. Fingolimod, a sphingosine-1-phosphate receptor modulator used in multiple sclerosis, acts in part through receptor internalization but also engages with the broader biology of sphingolipid-enriched membranes. Understanding how such agents redistribute membrane order across immune cell subsets could explain some of their off-target effects and guide the design of compounds that tune immune responses through membrane biophysics rather than direct receptor antagonism.

Methodological standardization remains an important challenge for the field. Different probes report on different aspects of membrane physics, and values obtained with one dye are not directly comparable to those from another without careful cross-calibration. Sample preparation, temperature, imaging parameters, and analysis pipelines all influence measured values, and the field has not yet converged on universally accepted reference standards. Efforts to establish standardized protocols, share calibration reagents, and report measurements in ways that facilitate comparison across laboratories will be essential if membrane order is to mature from a research measurement into a reproducible biomarker. The application of machine learning approaches to extract order-related features from large imaging datasets may also accelerate progress by identifying patterns that manual analysis would miss.

The diversity of immune cell subsets presents both an opportunity and a complication. Myeloid cells, lymphocytes, and innate lymphoid cells each maintain distinct lipidomes shaped by their developmental programs and functional demands. Within a single subset, activation state, differentiation stage, and tissue microenvironment further modify membrane composition. A dendritic cell maturing in response to pathogen-associated molecular patterns remodels its membrane as part of its transition from antigen capture to antigen presentation. Tissue-resident macrophages adapt their membrane properties to the lipid milieu of their organ of residence, which differs substantially between brain, lung, liver, and adipose tissue. Comprehensive maps of membrane order across this diversity would require systematic sampling, but the resulting atlas could reveal how physical membrane states encode functional specialization in ways that transcriptomic or proteomic measurements alone do not capture.

Looking forward, the integration of membrane order measurements with other single-cell modalities promises a more complete picture of immune regulation. Combining order imaging with live-cell reporters of signaling activity, such as fluorescent biosensors for kinase activity or calcium, would allow direct testing of causal relationships between membrane physics and signal transduction at the single-cell level. Pairing order measurements with lipidomics would connect physical readouts to their molecular determinants. Spatial transcriptomics and proteomics of tissue sections could place membrane biophysical states in their anatomical and pathological contexts. As these datasets accumulate, the plasma membrane’s physical organization may come to be recognized as a fundamental layer of cellular regulation, one that immune cells exploit with particular sophistication and one that offers distinct targets for therapeutic modulation of immunity.

Subject of Research: Plasma membrane order maps functional diversity in immune cells

Article Title: Plasma membrane order maps functional diversity in immune cells

Article References: Andronico, L. A., Gurdap, C. O., Arora, A., Ragaller, F., Sandoz, P. A., Jiang, Y., Giatrellis, S., de Boer, L. L., Carannante, V., Iskrak, S., Mikes, J., Buggert, M., Österborg, A., Önfelt, B., Klymchenko, A. S., Brodin, P., & Sezgin, E. (2026). Plasma membrane order maps functional diversity in immune cells. Nature Chemical Biology. https://doi.org/10.1038/s41589-026-02322-x

Image Credits: AI Generated

DOI: 10.1038/s41589-026-02322-x

Keywords: Plasma, membrane, order, maps, functional, diversity, immune, cells, scientific research