Expansion Kinetics Research Articles

Adaptive Cell Segmentation and Tracking for Volumetric Confocal Microscopy Images of a Developing Plant Meristem

Automated segmentation and tracking of cells in actively developing tissues can provide high-throughput and quantitative spatiotemporal measurements of a range of cell behaviors; cell expansion and cell-division kinetics leading to a better understanding of the underlying dynamics of morphogenesis. Here, we have studied the problem of constructing cell lineages in time-lapse volumetric image stacks obtained using Confocal Laser Scanning Microscopy (CLSM). The novel contribution of the work lies in its ability to segment and track cells in densely packed tissue, the shoot apical meristem (SAM), through the use of a close-loop, adaptive segmentation, and tracking approach. The tracking output acts as an indicator of the quality of segmentation and, in turn, the segmentation can be improved to obtain better tracking results. We construct an optimization function that minimizes the segmentation error, which is, in turn, estimated from the tracking results. This adaptive approach significantly improves both tracking and segmentation when compared to an open loop framework in which segmentation and tracking modules operate separately.

A study of Mg and Cu additions on the foaming behaviour of Al–Si alloys

Aluminium casting alloys containing Mg and Cu in addition to Si were investigated with respect to their potential to be foamed. The kinetics of foam expansion of different alloys was studied and the resulting structures were characterised. Of the stages of evolution of foams, namely (i) pore nucleation, (ii) foam growth in the semisolid state, (iii) further expansion in the fully liquid state, the latter two were explored. Expansion in the semisolid state could be related to the available liquid fraction. Mg-containing Al–Si alloys yielded a less coarse and more uniform pore structure than the other alloys investigated. However, achieving a high volume expansion required restriction to a narrow process window and led to the suggestion of AlMg4Si8 as a practical alloy.

Spectratyping analysis of the islet-reactive T cell repertoire in diabetic NOD Igμnull mice after polyclonal B cell reconstitution

BackgroundNon Obese Diabetic mice lacking B cells (NOD.Igμnull mice) do not develop diabetes despite their susceptible background. Upon reconstitution of B cells using a chimera approach, animals start developing diabetes at 20 weeks of age.MethodsWe have used the spectratyping technique to follow the T cell receptor (TCR) V beta repertoire of NOD.Igμnull mice following B cell reconstitution. This technique provides an unbiased approach to understand the kinetics of TCR expansion. We have also analyzed the TCR repertoire of reconstituted animals receiving cyclophosphamide treatment and following tissue transplants to identify common aggressive clonotypes.ResultsWe found that B cell reconstitution of NOD.Igμnull mice induces a polyclonal TCR repertoire in the pancreas 10 weeks later, gradually diversifying to encompass most BV families. Interestingly, these clonotypic BV expansions are mainly confined to the pancreas and are absent from pancreatic lymph nodes or spleens. Cyclophosphamide-induced diabetes at 10 weeks post-B cell reconstitution reorganized the predominant TCR repertoires by removing potential regulatory clonotypes (BV1, BV8 and BV11) and increasing the frequency of others (BV4, BV5S2, BV9, BV16-20). These same clonotypes are more frequently present in neonatal pancreatic transplants under the kidney capsule of B-cell reconstituted diabetic NOD.Igμnull mice, suggesting their higher invasiveness. Phenotypic analysis of the pancreas-infiltrating lymphocytes during diabetes onset in B cell reconstituted animals show a predominance of CD19+ B cells with a B:T lymphocyte ratio of 4:1. In contrast, in other lymphoid organs (pancreatic lymph nodes and spleens) analyzed by FACS, the B:T ratio was 1:1. Lymphocytes infiltrating the pancreas secrete large amounts of IL-6 and are of Th1 phenotype after CD3-CD28 stimulation in vitro.ConclusionsDiabetes in NOD.Igμnull mice appears to be caused by a polyclonal repertoire of T cell accumulation in pancreas without much lymphoid organ involvement and is dependent on the help by B cells.

Synthesis of novel 5-alkyl/aryl/heteroaryl substituted diethyl 3,4-dihydro-2H-pyrrole-4,4-dicarboxylates by aziridine ring expansion of 2-[(aziridin-1-yl)-1-alkyl/aryl/heteroaryl-methylene]malonic acid diethyl esters

A novel synthetic methodology has been developed for the synthesis of diethyl 5-alkyl/aryl/heteroaryl substituted 3,4-dihydro-2H-pyrrole-4,4-dicarboxylates (also called 2-substituted pyrroline-4,5-dihydro-3,3-dicarboxylic acid diethyl esters) by iodide ion induced ring expansion of 2-[(aziridin-1-yl)-1-alkyl/aryl/heteroaryl-methylene]malonic acid diethyl esters in very good to excellent yields under mild reaction conditions. The electronic and steric impact of the substituents on the kinetics of ring expansion of N-vinyl aziridines to pyrrolines has been studied. Various diversely substituted novel pyrroline derivatives have been synthesized by this methodology and the products can be used as key intermediates in the synthesis of substituted pyrrolines, pyrroles and pyrrolidines.

Individual and synergistic cytokine effects controlling the expansion of cord blood CD34+ cells and megakaryocyte progenitors in culture

Expansion of hematopoietic progenitors ex vivo is currently investigated as a means of reducing cytopenia following stem cell transplantation. The principal objective of this study was to develop a new cytokine cocktail that would maximize the expansion of megakaryocyte (Mk) progenitors that could be used to reduce periods of thrombocytopenia. We measured the individual and synergistic effects of six cytokines [stem cell factor (SCF), FLT-3 ligand (FL), interleukin (IL)-3, IL-6, IL-9 and IL-11] commonly used to expand cord blood (CB) CD34(+) cells on the expansion of CB Mk progenitors and major myeloid populations by factorial design. These results revealed an elaborate array of cytokine individual effects complemented by a large number of synergistic and antagonistic interaction effects. Notably, strong interactions with SCF were observed with most cytokines and its concentration level was the most influential factor for the expansion and differentiation kinetics of CB CD34(+) cells. A response surface methodology was then applied to optimize the concentrations of the selected cytokines. The newly developed cocktail composed of SCF, thrombopoietin (TPO) and FL increased the expansion of Mk progenitors and maintained efficient expansion of clonogenic progenitors and CD34(+) cells. CB cells expanded with the new cocktail were shown to provide good short- and long-term human platelet recovery and lymphomyeloid reconstitution in NOD/SCID mice. Collectively, these results define a complex cytokine network that regulates the growth and differentiation of immature and committed hematopoietic cells in culture, and confirm that cytokine interactions have major influences on the fate of hematopoietic cells.

Increased Memory Conversion of Naïve CD8 T Cells Activated during Late Phases of Acute Virus Infection Due to Decreased Cumulative Antigen Exposure

BackgroundMemory CD8 T cells form an essential part of protective immunity against viral infections. Antigenic load, costimulation, CD4-help, cytokines and chemokines fluctuate during the course of an antiviral immune response thus affecting CD8 T cell activation and memory conversion.Methodology/Principal FindingsIn the present study, naïve TCR transgenic LCMV-specific P14 CD8 T cells engaged at a late stage during the acute antiviral LCMV response showed reduced expansion kinetics but greater memory conversion in the spleen. Such late activated cells displayed a memory precursor effector phenotype already at the peak of the systemic antiviral response, suggesting that the environment determined their fate during antigen encounter. In the spleen, the majority of late transferred cells exhibited a central memory phenotype compared to the effector memory displayed by the early transferred cells. Increasing the inflammatory response by exogenous administration of IFNγ, PolyI:C or CpG did not affect memory conversion in the late transferred group, suggesting that the diverging antigen load early versus later during acute infection had determined their fate. In agreement, reduction in the LCMV antigenic load after ribavirin treatment enhanced the contribution of early transferred cells to the long lasting memory pool.Conclusions/SignificanceOur results show that naïve CD8 cells, exposed to reduced duration or concentration of antigen during viral infection convert into memory more efficiently, an observation that could have significant implications for vaccine design.

Three-dimensional atomistic modeling of microcrack propagation in iron

This paper presents the results of molecular dynamics modeling of quasi-brittle microcrack propagation on the (0 0 1) plane of bcc iron. The nucleation and propagation of such cracks is accompanied by the emission of slip bands from the crack tips. The 3D nature of the model, in conjunction with a Voronoi decomposition post-processing technique, allows us to clarify the atomistic structure of slip bands and to follow the detailed kinetics of slip band expansion and interaction with other microstructural defects. The effects of simulation temperature and alternative defects (in particular, vacancies and micro-voids) on the crack propagation kinetics are discussed.

Vaccination with Ad5 Vectors Expands Ad5-Specific CD8+ T Cells without Altering Memory Phenotype or Functionality

BackgroundAdenoviral (Ad) vaccine vectors represent both a vehicle to present a novel antigen to the immune system as well as restimulation of immune responses against the Ad vector itself. To what degree Ad-specific CD8+ T cells are restimulated by Ad vector vaccination is unclear, although such knowledge would be important as vector-specific CD8+ T cell expansion could potentially further limit Ad vaccine efficacy beyond Ad-specific neutralizing antibody alone.Methodology/Principal FindingsHere we addressed this issue by measuring human Adenovirus serotype 5 (Ad5)-specific CD8+ T cells in recipients of the Merck Ad5 HIV-1 vaccine vector before, during, and after vaccination by multicolor flow cytometry. Ad5-specific CD8+ T-cells were detectable in 95% of subjects prior to vaccination, and displayed primarily an effector-type functional profile and phenotype. Peripheral blood Ad5-specific CD8+ T-cell numbers expanded after Ad5-HIV vaccination in all subjects, but differential expansion kinetics were noted in some baseline Ad5-neutralizing antibody (Ad5 nAb) seronegative subjects compared to baseline Ad5 nAb seropositive subjects. However, in neither group did vaccination alter polyfunctionality, mucosal targeting marker expression, or memory phenotype of Ad5-specific CD8+ T-cells.ConclusionsThese data indicate that repeat Ad5-vector administration in humans expands Ad5-specific CD8+ T-cells without overtly affecting their functional capacity or phenotypic properties. This is a secondary analysis of samples collected during the 016 trial. Results of the Merck 016 trial safety and immunogenicity have been previously published in the journal of clinical infectious diseases [1].Trial RegistrationClinicalTrials.gov NCT00849680 [NCT00849680]

CD4+CD25+ Treg regulate the contribution of CD8+ T‐cell subsets in repopulation of the lymphopenic environment

Peripheral T-cell expansion is of major relevance for immune function after lymphopenia. In order to promote regeneration, the process should result in a peripheral T-cell pool with a similar subpopulation structure as before lymphopenia. We investigated the repopulation of the CD8(+) central-memory T cells (T(CM) ) and effector-memory T cells (T(EM)) pools after adoptive transfer of sorted CD8(+) T cells from naïve, T(CM) and T(EM) subsets into T-cell-deficient hosts. We show that the initial kinetics of expansion are distinct for each subset and that the contribution to the repopulation of the CD8(+) T-cell pool by the progeny of each subset is not a mere function of its initial expansion. We demonstrate that CD4(+) CD25(+) Treg play a major role in the repopulation of the CD8(+) T-cell pool and that CD8(+) T-cell subsets impact on each other. In the absence of CD4(+) CD25(+) Treg, a small fraction of naïve CD8(+) T cells strongly proliferates, correlating with further expansion and differentiation of co-expanding CD8(+) T cells. CD4(+) CD25(+) Treg suppress these responses and lead to controlled repopulation, contributing decisively to the maintenance of recovered T(CM) and T(EM) fractions, and leading to repopulation of each pool with progeny of its own kind.

Porosity and stability of bread dough during proofing determined by video image analysis for different compositions and mixing conditions

A method was developed to study the modifications of volume and shape of wheat flour dough during fermentation process by digital camera. Various compositions and mixing conditions were implemented in order to prepare dough pieces with different rheological properties. Results were analyzed in terms of porosity and stability, defined as the shape ratio of the dough. The kinetics of the two variables, were fitted by simple mathematical models. Porosity evolution was a lot influenced by the composition of the dough and results were found in agreement with those obtained by X-Ray Microtomography, but less by the mixing conditions. Conversely, the stability was favoured by larger levels of specific mixing energy, in the range (20, 60 kJ/kg). The interpretation of these results suggested that gas production is the main variable governing expansion kinetics whereas rheological properties, mainly strain hardening, has the most significant role on stability.

Comprehensive and semi-quantitative TCR repertoire analysis with a novel multiplex PCR method and 454 sequencing (85.3)

Abstract CDR3 sequences, composed by V(D)J combination, form the center of the antigen binding site where they often play a critical role in defining the affinity and specificity of the receptor for individual peptide-MHC complexes of both the TCRα and TCRβ chains. The goal of our study was to produce comprehensive, unrestricted profiles of TCR diversity among key developmental and effector subsets of T cells isolated from the blood of a single, healthy donor at sequence-level resolution using a novel multiplex PCR method combined with Roche 454 Life Sciences high-throughput sequencing technology. From the sequence reads, about 1.48 million CDR3 intervals were identified, totaling 169,977 and 113,290 unique CDR3 intervals for TCRα and for TCRβ, respecitively. Our data also show numerous examples of identical CDR3 sequences shared by different T subsets. Using the compound Poisson process model, we estimated that the diversity of the TCRα and β chains expressed by our donor is around 0.47 x 106 and 0.35 x 106 unique CDR3 nucleotide sequences, respectively. Our comprehensive data demonstrates that our new method has overcome past challenges in studying the T cell immune repertoire and is highly sensitive, repeatable, and semi-quantitative. This approach provides a useful tool for assessing immune competence, tracking T cell expansion kinetics, assessing vaccine efficiency, and detecting antigen-specific T cell clones in patients with infection or cancer.

Kinetics of hematoma expansion in murine warfarin-associated intracerebral hemorrhage

Background and purpose The burden of intracerebral hemorrhage associated with oral anticoagulants (OAC-ICH) is growing. However, little is known about the pathophysiology of W-ICH. Herein, we refine a mouse model of OAC-ICH using repetitive T2* MRI to describe kinetics of hematoma enlargement, and establish a benchside point of care INR assay (PoC) for assessment of anticoagulation. Methods C57/BL6 mice drank warfarin (0.4 mg/kg/24 h) in their water. ICH was induced by stereotactic injection of collagenase type VII (0.045 U) into the left striatum. Hemorrhagic blood volume was quantified by MRI T2* images and on cryosections 48 h after ICH induction. Kinetics of hematoma expansion were compared in strongly, moderately, and non-anticoagulated mice using repeated MRI T2* imaging. The PoC INR technique was validated against standard laboratory INR, and tail vein bleeding time (TVBT). Results PoC INR correlated with central laboratory measurements ( r = 0.989; p < 0.0001) and with TVBT ( r = 0.982; p < 0.0001). Hematoma volume was 21.2 ± 6.7 mm 3 in heavily (PoC INR 4−5), 12.3± 4.8 in moderately (INR 2−3), and 8.6 ± 3.3 in non-anticoagulated mice (INR < 1.2). Hematoma volume determined from cryosections and T2* MRI correlated well ( r = 0.922). Strength of anticoagulation was associated with neurologic outcome. Hematoma enlargement occurred mainly during the first 3 h in anticoagulated mice. Conclusions PoC allows repeated benchside INR measurements in individual mice which reflect the level of anticoagulation. Stronger anticoagulation results in larger hematoma volumes. As hematoma enlargement occurs mainly during the first hours, potential hemostatic therapies should be tested early in this OAC-ICH model.

Low night Temperatures cause reduced tracheid expansion in Podocarpus Latifolius

The influence of low night temperatures on the kinetics of tracheid expansion of two-year-old Podocarpus latifolius (Thunb.) R.Br. ex Mirb. was studied in a growth chamber experiment. In experiment 1 the plants were exposed to an almost constant air temperature of 18 to 20°C, while in experiment 2 the air temperature was reduced from 20°C during the day to 6°C during the night. The formation of the cambium derivative cells and the kinetics of tracheid expansion were analysed by high resolution laser increment measurements in combination with microscopic methods (accuracy: ± 2 μm, spatial resolution of 9.7 to 13.1 μm, temporal resolution: 60 s). Low night temperatures had no significant influence on the rate of cambial cell divisions and the proportion of tracheids and parenchyma cells in the xylem. However, they irreversibly interrupted the expansion of differentiating tracheids causing a high proportion of flattened tracheids in the xylem of the plants grown under the conditions of experiment 2. The results indicate that large differences between day and night temperatures can be an important trigger for the variation of the wood structure in subtropical and tropical gymnosperms.

Expansion and Activation Kinetics of Immune Cells during Early Phase of GVHD in Mouse Model Based on Chemotherapy Conditioning

In the present paper, we have investigated early pathophysiological events in graft-versus-host disease (GVHD), a major complication to hematopoietic stem cell transplantation (HSCT). BLLB/c female mice conditioned with busulfan/cyclophosphamide (Bu-Cy) were transplanted with allogeneic male C57BL/6. Control group consisted of syngeneic transplanted Balb/c mice. In allogeneic settings, significant expansion and maturation of donor dendritic cells (DCs) were observed at day +3, while donor T-cells CD8+ were increased at day +5 (230%) compared to syngeneic HSCT. Highest levels of inflammatory cytokines IL-2, IFN-gamma, and TNF-alfa at day +5 matched T-cell activation. Concomitantly naïve T-cells gain effecr-memory phenotype and migrated from spleen to peripheral lymphoid organs. Thus, in the very early phase of GHVD following Bu-Cy conditioning donor, DCs play an important role in the activation of donor T cells. Subsequently, donor naïve T-cells gain effector-memory phenotype and initiate GVHD.

Identification of variables that optimize isolation and culture of multipotent mesenchymal stem cells from equine umbilical-cord blood

OBJECTIVE-To optimize the isolation and culture of mesenchymal stem cells (MSCs) from umbilical-cord blood (UCB), identify variables that predicted successful MSC isolation, and determine whether shipping, processing, and cryopreservation altered MSC viability, recovery rates, and expansion kinetics. SAMPLE POPULATION-UCB samples from 79 Thoroughbred and Quarter Horse mares. PROCEDURES-UCB samples were processed to reduce volume and remove RBCs. Nucleated cells (NCs) were cryopreserved or grown in various culture conditions to optimize MSC monolayer expansion and proliferation. Donor and UCB-sample factors were analyzed to determine their influence on the success of MSC isolation and monolayer expansion. RESULTS-MSCs capable of multilineage in vitro differentiation were expanded from > 80% of UCB samples. Automated UCB processing and temperature-controlled shipping facilitated sterile and standardized RBC reduction and NC enrichment from UCB samples. The number of NCs after UCB samples were processed was the sole variable that predicted successful MSC expansion. The UCB-derived MSCs and NCs were successfully cryopreserved and thawed with no decrease in cell recovery, viability, or MSC proliferation. The use of fibronectin-coated culture plates and reduction of incubator oxygen tension from 20% to 5% improved the MSC isolation rate. Some UCB-derived MSC clones proliferated for > 20 passages before senescence. Onset of senescence was associated with specific immunocytochemical changes. CONCLUSIONS AND CLINICAL RELEVANCE-Equine UCB samples appeared to be a rich source of readily obtainable, highly proliferative MSCs that could be banked for therapeutic use.

Common Features of γδ T Cells and CD8+αβ T Cells Responding to Human Cytomegalovirus Infection in Kidney Transplant Recipients

Kidney transplant recipients infected with cytomegalovirus (CMV) undergo a persistent gammadelta T cell expansion in their peripheral blood. The anti-CMV function of these cells was previously demonstrated by their ability to kill CMV-infected cells in vitro. To gain insight into the role of gammadelta T cells within the antiviral immune network, we compared the expansion kinetics of these T cells with that of CMV pp65-specific CD8(+) alphabeta T cells in the peripheral blood of twenty-one kidney transplant recipients. Both the percentage and the absolute number of pp65-specific CD8(+) T cells and gammadelta T cells showed a concomitant increase and persistence in most of the kidney transplant recipients with CMV infection. Both cell subsets exhibited an effector/memory phenotype (CD28(-), CD27(-), and CD45RA(+)) that predominated for the entire follow-up period. In conclusion, CMV-specific CD8(+) alphabeta T cells and gammadelta T cells share common expansion kinetics and a common effector phenotype, suggesting that these cell types act similarly in response to CMV infection.

Phase behaviour and thermoelastic properties of perdeuterated ammonia hydrate and ice polymorphs from 0 to 2 GPa

The results are described of a series of neutron powder diffraction experiments over the pressure and temperature ranges 0 &lt;P&lt; 2 GPa, 150 &lt;T&lt; 240 K, which were carried out with the objective of determining the phase behaviour and thermoelastic properties of perdeuterated ammonia dihydrate (ND3·2D2O). In addition to the low-pressure cubic crystalline phase, ADH I, two closely related monoclinic polymorphs of ammonia dihydrate have been identified, which commonly occur as a composite in the range 450–550 MPa at 175 K; these are labelled ADH IIaand IIb, and each has unit-cell volumeV≃ 310 Å3and number of formula units per unit cellZ= 4. It has been determined that this composite dissociates to a mixture of ammonia monohydrate (ND3·D2O) phase II (AMH II) and ice II when warmed to ∼190 K at 550 MPa, which in turn partially melts to ice II + liquid atT= 196 K; AMH II has a large orthorhombic unit cell (V≃ 890 Å3,Z= 16). Above 600 MPa, an orthorhombic polymorph of ammonia dihydrate (withV≃ 530 Å3,Z= 8), which has been referred to previously as ADH IV, persists to pressures greater than 2 GPa and appears to be the liquidus phase over this whole pressure range. This phase has been observed co-existing with ice II, ice VI and AMH II. The most plausible synthesis of the high-pressure phase behaviour is described here. This model explains the reported observations, and provides measurements of the densities, thermal expansion, bulk moduli and crystal growth kinetics of the high-pressure ammonia dihydrate, ammonia monohydrate and ice polymorphs.

Late Stent Expansion and Neointimal Proliferation of Oversized Nitinol Stents in Peripheral Arteries

For peripheral endovascular intervention, self-expanding (SE) stents are commonly oversized in relation to target arteries to assure optimal wall apposition and prevent migration. However, the consequences of oversizing have not been well studied. The purpose of this study was to examine the effects of SE stent oversizing (OS) with respect to the kinetics of late stent expansion and the long-term histological effects of OS. Pairs of overlapped 8 x 28-mm Nitinol SE stents were implanted into the iliofemoral arteries of 14 Yucatan swine. Due to variations in target artery size, the stent-to-artery ratio ranged from 1.2:1 to 1.9:1. Lumen and stent diameters were assessed by quantitative angiography at the time of implantation. Following angiographic assessment at 6 months, stented arteries were perfusion-fixed, sectioned, and stained for histological analysis. Immediately following implantation, the stents were found to be expanded to a range of 4.7-7.1 mm, largely conforming to the diameter of the recipient target artery. The stents continued to expand over time, however, and all stents had enlarged to nearly their 8-mm nominal diameter by 6 months. The histological effects of OS were profound, with marked increases in injury and luminal area stenosis, including a statistically significant linear correlation between stent-to-artery ratio and area stenosis. In this experimental model of peripheral endovascular intervention, oversized Nitinol SE stents are constrained by their target artery diameter upon implantation but expand to their nominal diameter within 6 months. Severe OS (stent-to-artery ratio >1.4:1) results in a profound long-term histological response including exuberant neointimal proliferation and luminal stenosis.

Kinetics of Expansion of Epitope-Specific T Cell Responses during Primary HIV-1 Infection

Multiple lines of evidence support a role for CD8(+) T cells in control of acute/early HIV replication; however, features of the primary HIV-specific CD8(+) T cell response that may impact on the efficiency of containment of early viral replication remain poorly defined. In this study, we performed a novel, comprehensive analysis of the kinetics of expansion of components of the HIV-specific CD8(+) T cell response in 21 acutely infected individuals. Epitope-specific T cell responses expanded asynchronously during primary infection in all subjects. The most rapidly expanded responses peaked as early as 5 days following symptomatic presentation and were typically of very limited epitope breadth. Responses of additional specificities expanded and contracted in subsequent waves, resulting in successive shifts in the epitope immunodominance hierarchy over time. Sequence variation and escape were temporally associated with the decline in magnitude of only a subset of T cell responses, suggesting that other factors such as Ag load and T cell exhaustion may play a role in driving the contraction of HIV-specific T cell responses. These observations document the preferential expansion of CD8(+) T cells recognizing a subset of epitopes during the viral burst in acute HIV-1 infection and suggest that the nature of the initial, very rapidly expanded T cell response may influence the efficiency with which viral replication is contained in acute/early HIV infection.

Kinetics of myogenic progenitor cell (MPC) expansion and bone marrow‐derived cell recruitment in skeletal muscle regeneration

Muscle regeneration requires myogenic progenitor cells (MPC) and recruitment of bone marrow (BM)‐derived cells. MPC (CD34+/CD45−/Sca‐1−) and BM‐derived progenitor cells (CD45+/Sca‐1+) isolated from injured muscle undergo myogenic differentiation in vitro. However, the kinetics of MPC expansion and BM‐derived cell recruitment to injured muscle are poorly understood and were quantitated in tibialis anterior muscle using flow cytometry after cardiotoxin (CTX) injury in wild type (WT, C57Bl/6J) male mice. Maximal MPC expansion occurred 3 days post‐CTX and BM‐derived progenitor and immune cell recruitment exhibited similar kinetics; few cells present at baseline with maximal accumulation 3 days post‐CTX.MPC expansion and BM‐derived cell recruitment occurred within days of injury and demonstrated similar accumulation kinetics suggesting interactions between MPC and BM‐derived cells may be crucial to skeletal muscle regeneration. A better understanding of interactions between different cell types could result in improved strategies for muscle regeneration and tissue engineering.Supported by Veterans Administration and HL074236 and HL090196.