{"id":"26e9df63-931e-49bd-aceb-d016edbe324d","arxiv_id":"2601.20719","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":7,"one_line_summary":"A curvature–actin membrane model predicts biting, pushing, or full engulfment of deformable targets depending on target stiffness, matching macrophage–GUV and macrophage–lymphoma observations.","lead":"Using a computer simulation of two bendable membranes, researchers show that target stiffness decides whether an immune cell takes a bite, pushes away, or fully swallows a target — and the same three behaviors appear in experiments with artificial vesicles and lymphoma cells. The work suggests mechanical cues help immune cells choose how to clear targets.","discovery_kind":"first_principles","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 'biting' regime is not actually simulated: fission is explicitly disallowed, so the model produces only stalled partial engulfment, and the abstract's claim that it predicts trogocytosis/extraction is an unsupported extrapolation.","rationale":"The reader's verdict (CONDITIONAL) is appropriate, but the reader's stated weakest assumption—that the target is modeled as a pure bilayer without cortex/nucleus—is not the single most load-bearing gap. The more direct internal gap is that the model explicitly forbids the topological change needed for trogocytosis. The abstract's first predicted regime is therefore not a prediction of biting but of stalled partial engulfment; the biological interpretation is an extrapolation. This concern is explicitly acknowledged in the manuscript, which strengthens rather than weakens the point: the authors know fission is absent and still call the stalled state 'biting.' A concrete computational test—adding a scission rule—would settle whether the stalled partial engulfment would actually produce a fragment. If it does not, the three-regime phase diagram remains useful for engulfment vs. pushing, but the trogocytosis claim would need to be downgraded. The reader's rationale did mention this issue ('biting is inferred from a stalled partial engulfment without fission'), so my concern partially overlaps with the reader's, but the reader did not make it the central weakest assumption. I therefore keep the verdict at CONDITIONAL/UNCHANGED: the paper is worth conditional acceptance, but the abstract and discussion should be revised to avoid claiming the simulation produces extraction when it does not.","tokens_in":27388,"tokens_out":9617,"duration_ms":127363,"concrete_test":"Implement a minimal scission move in the triangulated MC model—e.g., allow a vesicle to split when the neck radius at the engulfment rim falls below l_min and the local bending-energy cost exceeds a threshold—and rerun the κ sweep in the 'biting' range (κ = 20–60 kBT). Determine whether a separated target fragment actually forms and whether the Aad/A plateau persists or resolves into retraction/engulfment. If no fragment forms without adding extra contractile or adhesive machinery, the 'biting' phase should be relabeled 'partial engulfment' and the abstract's 'where part of the target is extracted' is unsupported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim includes a predicted 'biting (trogocytosis)' regime in which 'part of the target is extracted.' But the simulation never extracts part of the target: the text states 'Note that we do not allow the vesicles to undergo fission' (Fig. 4 caption) and 'we do not allow our vesicles to undergo topological changes such as fission, so the biting behaviour in the simulations is arrested' (Discussion). What is actually simulated in the low-κ regime is a stalled partial engulfment with Aad/A < 0.5. The leap from that stalled state to a real 'bite' requires that fission would occur, but no model for scission is provided, and no evidence is given that the stall would resolve by fission rather than by retraction (as in the pushing regime) or by eventual full engulfment on longer timescales. Since the claimed mechanism—curvature–actin feedback altering force orientation—explains why engulfment stalls, it does not by itself explain why a part detaches. The abstract therefore overstates what the model predicts. The experimental observation of real trogocytosis does not close this gap, because the model is not shown to produce the same topological outcome.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper extends a previously published Monte Carlo triangulated-vesicle model of curvature–actin coupling to two interacting vesicles, treating both the phagocyte-like vesicle and the target as deformable membranes. After benchmarking against analytic adhesion results and the rigid-sphere limit, the authors vary the target's bending rigidity (or internal pressure) and report three dynamical regimes: 'biting' (stalled partial engulfment with adhered-area fraction below 0.5), 'pushing' (transient contact followed by detachment), and full engulfment. They argue that the regime boundary is set by feedback between target deformation and the tangential/normal orientation of active forces. Qualitative comparison is made with macrophage engulfment of GUVs, lymphoma cells, and deformable microparticles. The abstract frames the work as predicting that target stiffness governs distinct phagocytic modes, including trogocytosis.","tokens_in":27773,"tokens_out":3173,"duration_ms":41030,"significance":"If the central claim stands, the paper provides a mechanistic, parameter-light explanation for why immune cells engulf stiff targets but push away or partially engulf soft ones, and it connects the simulation observables to force-orientation feedback. The manuscript has real strengths: the code/algorithm is benchmarked against analytic adhered-vesicle results and the rigid-sphere limit; the parameters are mostly taken from prior work rather than fitted to the new experiments; the κ- and pressure-variation phase sequences are internally consistent; and the experimental imaging provides qualitative support for the pushing and engulfment regimes. However, the headline 'biting/trogocytosis' regime is not actually simulated: fission is explicitly disallowed, so the low-stiffness outcome is a stalled partial engulfment. This gap directly affects the abstract's main claim and must be addressed before the paper can be accepted.","major_comments":[{"comment":"The abstract states the model 'predicts three mechanical regimes ... (i) biting (trogocytosis), where part of the target is extracted,' but the simulations never extract a part: Fig. 4's caption says 'we do not allow the vesicles to undergo fission,' and the Discussion says 'so the biting behaviour in the simulations is arrested.' What is actually computed in the low-κ regime is a stalled partial engulfment with Aad/A<0.5. No scission mechanism is supplied, and no evidence rules out eventual retraction (as in the pushing regime) or slower full engulfment. The claim that the model predicts trogocytosis therefore outruns the simulation; either a topological fission step must be added or the 'biting' label must be changed to 'stalled partial engulfment,' with the trogocytosis connection presented only as a speculative extrapolation.","section":"Abstract; Fig. 4C and caption; Discussion"},{"comment":"The interaction energy Wint applies an active force from the cell-like vesicle to target vertices without an explicit reaction force on the cell-like vesicle; the text acknowledges 'we do not explicitly maintain force balance' and argues that free vesicles are effectively balanced in the center-of-mass frame. Because the central mechanism is the feedback between target deformation and force orientation, the absence of local momentum conservation could in principle alter the cup-shape dynamics and the stall that is labeled 'biting.' The authors should either implement reaction forces and show that the three regimes are unchanged, or provide a specific argument why the missing reaction force cannot affect the phase boundaries.","section":"Theoretical Model, Eq. (1); p.2"},{"comment":"The simulations vary target bending rigidity κ or osmotic pressure p, but the cellular targets (lymphoma cells, apoptotic cells) resist deformation primarily through cortical actomyosin tension and internal structure, not membrane bending. The manuscript asserts an equivalence ('effectively stiffening the vesicle') without a quantitative mapping between the simulated κ/p values and cortical stiffness. This is load-bearing for the claim that target mechanics—rather than a particular model mechanism—determines the regimes. At minimum, the authors should estimate the physical ranges of κ and p used here, or include an explicit surface-tension/cortical-tension term and test whether the regime order is preserved.","section":"Comparison to experiments; Fig. 7"}],"minor_comments":[{"comment":"Typo: 'phagocytosis o f soft, deformable targets' should be 'phagocytosis of soft, deformable targets.'","section":"Title"},{"comment":"The citation placeholder '[ ? ]' appears after the osmotic-pressure energy term; the missing reference should be supplied.","section":"Supplementary Eq. (S12)"},{"comment":"Units of the active force are inconsistent: the main text gives F = 2 kBT/lmin and the SI Fig. S6 caption gives F = 2 kBT lmin^-2. Please unify and define the dimensionality of F in Eq. (S3).","section":"Methods and SI"},{"comment":"Panel labels in Fig. 5 use inconsistent capitalization ('H)-j)'); also 'Ffraction' appears in Fig. 4B. Please clean up the axis labels and panel callouts.","section":"Fig. 5 labels"},{"comment":"Volume is not conserved by default, and the symmetry-breaking transition in Fig. 2 involves large volume changes. The text should state explicitly which production runs conserve volume and which do not, and how this choice affects the interpretation of the engulfment/pushing regimes for real cells.","section":"Results, Fig. 2 and Methods"}],"recommendation":"major_revision","confidential_remarks":"This is a serious modeling paper with valuable benchmarks and qualitative experimental support. The main obstacle is the 'biting/trogocytosis' framing: the simulation forbids fission and therefore cannot produce the topological outcome advertised in the abstract. That is a correctable issue—either by adding a scission model or by reframing the third regime as stalled partial engulfment with trogocytosis as an untested extrapolation—but it is central enough that I cannot recommend acceptance in the current form. The force-balance and target-mechanics mapping issues strengthen the need for major revision but are secondary."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take on arXiv:2601.20719. The model is a genuine extension of the authors' curvature–actin (CMC) phagocytosis framework from rigid targets to two deformable vesicles. The new thing is the phase diagram: with increasing target bending rigidity or internal pressure, the cell-like vesicle goes from stalled partial engulfment to pushing/leaving to full engulfment. The mechanism — target deformation tilts active forces away from tangential alignment and arrests cup spreading — is plausible and emerges from the dynamics, not from fitting to the new experiments. The validation is solid: benchmarks against analytic vesicle-adhesion results and against their own rigid-sphere limit, and the pressure-driven phases match the rigidity-driven ones. The experiments are a real bonus: GUVs at different sucrose concentrations and lymphoma cells show engulfment, pushing, and trogocytosis, and the DAAM-particle traction data show qualitatively similar force localization. The individual experimental phenomena were mostly known; organizing them under one mechanical axis is the contribution.\n\nNow the soft spots, in order of size. First, the abstract overclaims. The model does not simulate a bite or extraction of target material. The text is explicit: fission is disallowed, so the lowest-rigidity regime is a stalled partial engulfment with Aad/A < 0.5. Calling that \"biting (trogocytosis), where part of the target is extracted\" is an extrapolation. The leap from stall to bite requires scission, and nothing in the model explains why the stall resolves by fission rather than retraction or full engulfment on longer timescales. The authors disclose this in the figures and discussion, but the abstract and title lean on the word \"biting.\" That mismatch should be fixed, either by softening the language or by adding a scission criterion. Second, force balance: active forces are applied to the target without an equal and opposite force on the cell vesicle. They say momentum sinks or the center-of-mass frame handle this. For the pushing phase, this could matter, since net forces on a free vesicle are involved. I would want a check that relative dynamics don't depend on this. Third, the phase boundaries come from single runs; no error bars or ensemble averaging. The plateau curves look clean, but a few replicates would firm up the diagram. Fourth, the mapping to cells is qualitative. Real targets carry a cortex and internal structure; a pure lipid vesicle's bending rigidity is not obviously the same knob as cortical tension in a lymphoma cell. The GUV experiments vary osmotic pressure, not bending rigidity, and the model's pressure axis does mimic that, so it's less of a stretch — but the stiffness attribution for the lymphoma cells is not measured.\n\nNone of this is fatal. The central idea — target deformability, not just rigidity, selects the interaction mode — holds up, and the simulation mechanics are reasonable for the questions asked. I would send this to a good referee. For my own work I would cite the model, not the abstract's trogocytosis claim. Recommendation: engage; ask for a revision that either simulates scission or rephrases the biting claim, plus some measure of uncertainty on the phase boundaries.","headline":"The paper's real contribution is a two-vesicle simulation showing target deformability selects engulfment vs pushing; the 'biting/trogocytosis' label overstates what is simulated, since fission is explicitly disallowed.","tokens_in":28250,"tokens_out":2083,"would_cite":true,"duration_ms":24338,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":["92C37","92C10"],"pacs":["87.17.Aa","87.17.Jj"],"model":"deepseek-v4-flash","headline":"A two-vesicle simulation predicts that target stiffness dictates whether a phagocyte bites, pushes, or engulfs, via feedback between target deformation and the orientation of actin-driven forces.","keywords":["phagocytosis","trogocytosis","target stiffness","membrane bending rigidity","curvature-actin coupling","Monte Carlo vesicle model","actin polymerization","engulfment regimes"],"falsifier":"Measure the same three interaction modes while independently changing cortical tension without altering membrane bending rigidity—for example, using micropipette aspiration or drugs that disrupt the actin cortex on target cells. If pushing still occurs for low-bending targets, or if engulfment fails for cortex-free but stiff GUVs, then the proposed mechanical phase boundaries are wrong. A more direct test is to track the tangential versus normal force fraction at the leading edge: the model predicts a high normal fraction in the pushing phase and a high tangential fraction in engulfment, which","tokens_in":1425,"feed_emoji":"🦠","tokens_out":3202,"duration_ms":69621,"temperature":0.7,"pith_summary":"The paper tries to show that the mechanical deformability of a phagocytic target is not a side detail but a decisive control parameter. Using a two-vesicle Monte Carlo membrane model with curvature-sensitive actin-recruiting protein complexes, it predicts three regimes with increasing target stiffness: biting (trogocytosis), pushing away, and complete engulfment. The same transitions appear when target membrane tension is raised instead of bending rigidity, suggesting a unified mechanical origin. The authors back the predictions with live-cell experiments in which macrophages engulf, push, or bite GUVs and lymphoma cells of different tensions. If correct, target mechanics becomes a handle for controlling whether immune cells clear a target, destroy it by nibbling, or leave it alone.","feed_headline":"Target stiffness decides if immune cells bite, push, or engulf","feed_subtitle":"Soft targets get nibbled, mid-stiff targets get shoved, rigid targets get swallowed — in simulations and live-cell videos.","key_machinery":"The central object is a pair of dynamically triangulated, self-avoiding vesicles interacting through adhesion and through local forces applied by curved membrane protein complexes (CMC). The CMC have an intrinsic curvature that recruits actin-like active forces, and the delivered force on a target node is decomposed into tangential and normal components relative to the target surface. The load-bearing mechanism is the shape-force feedback: target deformation changes the local normal, which reorients the active force, which in turn either promotes spreading (tangential dominance) or arrests it (normal dominance). The same phase behaviour is obtained by tuning bending rigidity or internal pres","core_discovery":"The central claim is that the outcome of phagocytosis of a deformable target is set by a feedback loop between the target's shape change and the orientation of active protrusive forces exerted by the cell's leading edge. In the simulations, curved membrane complexes (CMC) recruit actin-like normal forces, and the target vesicle deforms in response. For a stiff target, the CMC cluster aligns tangentially at the leading edge, driving efficient engulfment. For intermediate stiffness, the target deforms enough that the leading-edge force stays partially normal, arresting cup spreading and ending in a push-then-detach event. For the softest targets, large deformation keeps both normal and tangent","pith_inferences":["A testable extension is to measure the rigidity of individual lymphoma cells before contact and correlate it with the observed macrophage behavior; the model predicts a sharp stiffness threshold between pushing and engulfment.","The phase diagram suggests a potential immune-evasion strategy: a target that softens itself (e.g., by loosening its cortex) could shift from being engulfed to being bitten or pushed, which may be relevant to tumor cell heterogeneity.","The equivalence of bending rigidity and internal pressure in the model hints that cellular osmotic regulation could be a fast, reversible way for targets to modulate their own fate during immune attack.","If the force-orientation feedback is the real driver, then therapies that alter actin organization at the leading edge rather than target stiffness should also shift the phase boundaries, a prediction that could be probed with cytoskeletal drugs."],"forward_implications":["If the central claim is correct, target stiffness alone can switch an immune cell between engulfment, pushing, and trogocytosis, making mechanics a functional input to immune clearance.","The push-and-detach regime predicts that intermediate-stiffness targets can survive contact by being displaced rather than internalized, which could explain how some apoptotic or tumor cells evade clearance.","The model implies that raising target tension or rigidity—for example through crosslinking or osmotic stress—could convert a biting interaction into full engulfment, suggesting a mechanical route to enhance phagocytosis.","Confinement or tethering of a target changes the outcome from pushing to engulfment or biting, so the same cell-target pair may behave differently in tissue versus suspension.","Because weaker active forces suffice to engulf soft targets, the model predicts that excess protrusive force can be counterproductive for soft-target clearance."],"fun_headline_variants":["Target stiffness sets immune cell mode: bite, push, or engulf","Soft targets bitten, stiff engulfed, mid pushed: mechanics rule","Curvature-actin coupling links stiffness to bite, push, engulf","How stiff a target is decides if cells bite, push, or swallow"],"cache_read_input_tokens":29568,"weakest_assumption_plain":"The target is modeled as a pure lipid-bilayer vesicle, so its resistance comes only from membrane bending; real cells resist deformation mainly through their cortical actin network and internal structures, and if cortical tension rather than membrane bending sets target deformability, the predicted biting/pushing/engulfment thresholds may not transfer to living cells.","fun_headline_variants_meta":{"raw":{"variants":["Target stiffness sets immune cell mode: bite, push, or engulf","Soft targets bitten, stiff engulfed, mid pushed: mechanics rule","Curvature-actin coupling links stiffness to bite, push, engulf","How stiff a target is decides if cells bite, push, or swallow"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000725,"raw_usage":{"total_tokens":3067,"prompt_tokens":703,"completion_tokens":2364,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":447,"completion_tokens_details":{"reasoning_tokens":2299}},"tokens_in":447,"tokens_out":2364,"duration_ms":20112,"temperature":1.0,"reasoning_tokens":2299,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-03T07:16:02.644183+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the same three interaction modes while independently changing cortical tension without altering membrane bending rigidity—for example, using micropipette aspiration or drugs that disrupt the actin cortex on target cells. If pushing still occurs for low-bending targets, or if engulfment fails for cortex-free but stiff GUVs, then the proposed mechanical phase boundaries are wrong. A more direct test is to track the tangential versus normal force fraction at the leading edge: the model predicts a high normal fraction in the pushing phase and a high tangential fraction in engulfment, which","supporting_citations":[],"review_version":1}