Cross-Talk Between Neutrophils and Macrophages Post-Myocardial Infarction: From Inflammatory Drivers to Therapeutic Targets

The initial inflammatory phase of myocardial infarction (day 1–3) represents the clearest window in which monocyte–neutrophil crosstalk occurs, either directly or indirectly. DAMPs released from ischemic tissue activate PRRs on surviving cells, including resident CCR2⁺ macrophages [5]. These macrophages, in turn, secrete inflammatory cytokines and chemokines that recruit circulating leukocytes, including neutrophils, marking the first level of neutrophil–macrophage communication (Figure 1). Infiltrating neutrophils peak around day 1 post-MI [33], and produce chemokines that signal monocytes to migrate to the lesion site (a second level of communication). Under the influence of local inflammatory cues (many of which are provided by neutrophils), monocytes differentiate into CCR2⁺Ly6C^high pro-inflammatory macrophages, a third level of cross-talk. These macrophages actively phagocytose cellular debris, including apoptotic neutrophils, and further amplifying inflammation through the secretion of IL-1β, IL-6, and TNF-α. While neutrophils release inflammatory mediators that exacerbate tissue damage and promote additional immune-cell recruitment [34], they also aid debris clearance and are required for efficient macrophage efferocytosis and polarization toward an M2-like reparative phenotype [35], highlighting that neutrophil–macrophage interaction may participate in the initiation of the reparative phase post-MI, marking a fourth level of interaction (Figure 1). This phase involves the gradual resolution of inflammation, myofibroblast proliferation, and scar formation, typically starting from day 4 to day 7 post-MI. After the first 3 days, anti-inflammatory mediators increase, limiting neutrophil infiltration, enhancing macrophage efferocytosis of apoptotic neutrophils, and possibly promoting the transition of CCR2⁺Ly6C^high recruited macrophages toward reparative phenotypes [24]. There is evidence showing that NGAL (neutrophil gelatinase-associated lipocalin) from the neutrophil secretome modulates efferocytosis by regulating the expression of efferocytosis receptor MertK (myeloid-epithelial-reproductive tyrosine kinase) on the membrane of cardiac macrophages [32]. In addition, DNA from NETs can prime Mertk⁻MHC-II^lo-int macrophage polarization through the TLR9 pathway, although the precise mechanisms remain to be defined [36]. Both examples illustrate an indirect mode of communication, whereby neutrophil-derived factors modulate macrophage functionality.

Resolution of the inflammatory phase marks the transition to the proliferative phase, a process characterized by angiogenesis and collagen deposition by myofibroblasts, ultimately leading to the development of scar tissue. During this stage, inflammatory leukocytes are either cleared from the injured tissue or transformed into reparative phenotypes that secrete anti-inflammatory, pro-angiogenic, and pro-fibrotic mediators [37]. Collectively, current evidence indicates that neutrophil–macrophage cross-talk occurs predominantly during the inflammatory and early reparative phases of MI, while much less is known about their interactions during the later proliferative phase.

Macrophages were initially categorized into polarized M1/M2 states; by analogy, N1/N2 neutrophils were proposed in the infarct area based on the gene expression profiling of isolated cardiac neutrophils using pro- and anti-inflammatory markers. In this manner, it was shown that pro-inflammatory molecules (e.g., IL-1β, TNF-α, CCL3) peak on day 1 post-MI in isolated neutrophils, whereas anti-inflammatory markers increase around days 4–7 [17]. It is now clear, however, that both macrophages and neutrophils exhibit broad phenotypic heterogeneity beyond these binary definitions. Recent single-cell RNA-seq (scRNA-seq) studies have revealed transcriptionally distinct immune subpopulations and their dynamic flux after MI [38]. Because neutrophils are particularly sensitive to scRNA-seq workflows, many cardiac datasets under-capture their diversity, and instead predominantly describe the monocyte/macrophage continuum, but emerging studies are overcoming these limitations. Defining these subpopulations and their temporal trajectories could also shed light on the neutrophil–macrophage crosstalk and its influence on the progression versus resolution of inflammation.

A scRNA-seq study [18] mapping neutrophils on days 1, 2, or 3 post-MI identified five cardiac neutrophil states: Retnlg^HI, ISG^HI, NF-κB^HI, HIF-1^HI, and SiglecF^HI. Retnlg^HI neutrophils were the most abundant on day 1 and were also prominent in the steady-state heart. Notably, whereas other subsets declined by days 2 and 4, the SiglecF^HI population increased and reached ~54% of all cardiac neutrophils by day 4. These findings are supported by another study, which reported a similar SiglecF^HI neutrophil subset emerging from day 3 post-MI onward [14]. This SiglecF^HI population exhibits a pro-inflammatory phenotype with enriched NF-κB and Myc target activity and elevated expression of genes such as TNF, ICAM-1, Nlrp3, features consistent with enhanced longevity and sustained inflammatory signaling. By comparing aging and transcriptomic specifications in circulating versus myocardial neutrophils, these authors also showed that neutrophils can acquire specialized phenotypes locally within infarcted tissue. Both studies further identified a type-I interferon-responsive subset (ISG^HI) present in both normal tissue and blood, indicating that this state is not MI-specific [39].

Similar to neutrophils, macrophages can also assume multiple fates in the infarcted heart. One important distinction must be made between the recruited versus resident macrophages. CCR2 status was initially used as a marker of residency, with CCR2⁺ macrophages being considered monocyte-derived and CCR2⁻ cells viewed as seeding the heart during embryonic development [4]. However, scRNA-seq is revealing that some monocyte-derived macrophages express low CCR2, indicating that additional markers are required to discriminate these lineages. In a comprehensive 2022 study, Dick et al. showed that three resident subsets co-exist in the normal heart: a TLF⁺ population expressing TIMD4, LYVE1, FOLR2 with low CCR2 and self-renewal capacity; a CCR2⁺ subset with low TIMD4⁻LYVE1⁻FOLR2⁻, which is constantly replaced by monocytes; and a MHC-II^hi subset that lacked TLF subset genes and CCR2 expression [40]. A recent integrative study showed a macrophage cluster with high Lyve1 and Folr2 expression that was enriched in controls, declined rapidly by day 3 post-MI, and was again increased in the reparative phase after day 7 [41]. Chakarov et al. identified a similar macrophage population high in Lyve1 expression that was localized near blood vessels and had a potential role in facilitating vascular repair and regeneration through the release of vascular growth factors in response to injury [42]. The modulation of this cluster post-MI could prove useful in future therapeutic actions post-MI, as there is evidence that human Lyve⁺ macrophages can also interact with cardiac fibroblasts and influence cardiac fibrosis through the CD74-MIF axis [43].

For infiltrating macrophages, Ke et al. integrated multiple scRNA-seq and snRNA-seq datasets and resolved eight macrophage subclusters in mouse hearts [41]. One cluster with high Arg1, Ccl6, and Ccl2 expression expanded rapidly on day 1 post-MI and declined by day 5. In contrast, a Spp1⁺, Gpnmb⁺, Fabp5⁺ cluster expanded from day 3, peaked on day 7, and dropped sharply by day 14. In both mouse and human cardiac tissues, Spp1^high macrophages were almost exclusively present in early MI, not in later stages. Arg1 is a canonical marker for immunosuppressive M2 macrophages [44]; in postnatal day 1 (P1) vs. P10 mice hearts, myocardial injury was associated with an increased Arg1⁺ macrophage subpopulation in regenerative P1 hearts, correlating with improved repair. Interestingly, CXCR2 inhibition enhanced cardiac repair and further increased Arg1⁺ macrophages, but this effect was lost when neutrophils were depleted [45], underscoring the important role of neutrophils in post-MI repair.

While defining the transcriptomic signatures of neutrophil and macrophage subsets is essential, capturing their communication potential is paramount. scRNA-seq now enable inference of cell–cell interactions using tools such as Scriabin, NicheNet, LIANA+, Cellchat [46]. Applying NicheNet to neutrophil–macrophage signaling, Vafadarnejad et al. identified IL-1β, TNF-α, and Csf1 as top-ranked neutrophil ligands influencing macrophage programs, and highlighted Csf1/Csf1r and Vegfa/Nrp1 as key ligand-receptor pairs in this interaction. In addition, some ligands exhibited enrichment in neutrophils at different time points after MI, for example, TNF-α peaking on days 3 and 5 post-MI, and C3 and Ccl4 on day 1 post-MI, suggesting a time-dependent neutrophil/macrophage cross-talk [14].

Although scRNA-seq provides valuable insights into cellular transcriptomic heterogeneity and enables the inference of cell–cell communication, the required tissue dissociation results in the loss of spatial context. To overcome this limitation, spatial transcriptomics (ST) technologies preserve cellular localization and spatial relationships of neighboring cells. A recent study employing ST revealed that neutrophils highly infiltrate into the infarcted area on day 1 post-MI, whereas macrophages are mostly dispersed across the whole heart tissue. Furthermore, while early (days 1–3) and late (days 5 and 7 post-MI) macrophage subsets accumulate in the infarcted region, a subset of steady-state tissue resident macrophages remains dispersed across the myocardium at all time points, potentially modulating the immune response and promoting tissue repair [47].

Another comprehensive study employing both scRNA-seq and ST that focused on the cellular composition and distribution within the MI border zone revealed the presence of several myeloid subsets, including Lyve1^HI resident macrophages, monocyte-derived macrophages (Ly6c2^HI, Ifit1^HI, Arg1^HI, C1qa^HI, Gclm^HI), and neutrophils (Retnlg^HI, Siglecf^HI, Ifit1^HI) in the first 7 days post-MI. Macrophage subpopulations (C1qa^HI, Gclm^HI, Lyve1^HI) were located along the posterolateral wall of the LV, near the papillary muscle, while Arg1^HI pro-resolving macrophages were found in the anterior and anterolateral wall of the LV. Neutrophil markers (S100a8, S100a9) and fibrosis were also abundantly detected in this area, which is the most affected following the occlusion of the coronary artery. This data supports the potential for local interactions between the two cell populations and provides the necessary context for neutrophils to promote a pro-resolving macrophage phenotype. In addition, both Ifit1^HI macrophages and Ifit1^HI neutrophil subsets, which correspond to a mostly pro-inflammatory signature, were found to inhabit the same limited area in the anterior wall of the LV [48].

Therefore, despite major advances from time-resolved single-cell sequencing, we still lack a causally resolved, time-anchored map of how discrete neutrophil and macrophage subtypes communicate across infarct zones to govern the transition from inflammation to repair. Integrative frameworks for inferring cell–cell communication now exist, but they require further studies to move beyond correlation and establish signaling mechanisms. Systematic, phase-specific mapping of who talks to whom, when, and where will be essential to explain why similar cellular compositions can yield different remodeling trajectories after MI.

The neutrophil secretome—including cytokines, proteases, NETs, and extracellular vesicles—can influence the behavior of infiltrating monocytes and macrophages, controlling their polarization and function (Table 1). The factors released by neutrophils expand the inflammatory infiltrate but also create a microenvironmental context that primes macrophages either for pro-inflammatory or reparative functions, depending on the timing and balance of additional signals. Our recent data showed that macrophages exposed to the secretome from pro-inflammatory N1 neutrophils exhibit increased expression of TNF-α, IL-1β, and S100A8/A9, suggesting that factors released by these cells promote an M1-like inflammatory response in macrophages. In contrast, when macrophages were exposed to N2 secretome, they increased expression of the anti-inflammatory markers CD206, TGF-β, and IL-10 and of nuclear factors associated with reparatory macrophages (PPARγ, Nur77, and KLF4), indicating that factors released by N2 cells promote an M2-anti-inflammatory response [16]. Moreover, MerTK—an indispensable molecule for clearance of cell debris and inflammation resolution post-MI—together with other efferocytosis receptors were upregulated in macrophages following their exposure to soluble factors released by anti-inflammatory N2 neutrophils [16], highlighting the importance of neutrophil–macrophage cross-talk in promoting inflammation resolution. Therefore, this secretome-driven crosstalk plays a central role in the transition from inflammation to repair, potentially affecting processes such as macrophage recruitment, efferocytosis, and fibrotic remodeling. Among the factors contained in the neutrophil secretome that impact macrophage phenotype and functionality, there are as follows:

As stated, following MI, neutrophils are the first immune cells to infiltrate the injured myocardium, followed by monocytes. Most studies emphasize that infiltrating monocytes are modulated by neutrophils already present within the lesion, suggesting that the earliest cross-talk between these populations is directed from neutrophils toward monocytes/macrophages. Despite this, in the very early phase of MI, resident macrophages within the infarct zone are rapidly activated by local DAMPs and release chemokines that attract neutrophils. Thus, the first wave of crosstalk is actually directed from macrophages toward neutrophils. Therefore, it can be argued that resident macrophages play an initiating role in post-MI evolution by recruiting neutrophils to the lesion.

As reviewed in the previous section, many studies have investigated how neutrophils, or their released factors, influence macrophage phenotypes and functions. In contrast, only a limited number of studies have examined the reciprocal process—how macrophages affect neutrophil behavior. A recent study addressed this gap, showing that conditioned medium from activated human monocyte-derived macrophages enhances neutrophil activation by boosting both oxidative and glycolytic metabolism, while simultaneously impairing their migratory capacity, effectively retaining them at sites of injury. These neutrophils displayed elevated ROS production, increased NET formation, and enhanced secretion of CXCL8, IL-13, and IL-6 compared to untreated neutrophils or those exposed to conditioned medium from unstimulated macrophages [86].

The interplay between neutrophils and macrophages extends beyond cytokine and EV signaling to include a metabolic crosstalk within the infarcted tissue microenvironment. Cellular metabolism is a key determinant of immune cell function and plasticity, as demonstrated in T cells and macrophages [87]. In contrast, the metabolic regulation of neutrophil biology has only recently gained attention. Traditionally regarded as cells relying almost exclusively on glycolysis, neutrophils were thought to possess limited metabolic flexibility. However, recent advances have questioned this view, revealing that the tricarboxylic acid cycle, oxidative phosphorylation, fatty acid oxidation, and the pentose phosphate pathway all contribute to meet the energetic, biosynthetic, and functional demands of neutrophils [88,89,90,91]. Although the metabolic interplay between neutrophils and macrophages following MI has not yet been extensively investigated, emerging evidence suggests the existence of such a crosstalk. Recent data indicate that conditioned media from activated macrophages enhances neutrophil activation, as reflected by increased ROS production, elevated NET formation, and higher levels of CXCL8, IL-13, and IL-6. These changes were accompanied by an upregulation of both oxidative and glycolytic metabolism, while concurrently reducing neutrophil migratory capacity [86]. Moreover, metabolic intermediates produced by these two cell types, such as lactate, succinate, and arginine-derived metabolites, can profoundly influence neutrophil and macrophage polarization and behavior by modulating their activation, lifespan, and effector functions. Therefore, the acute inflammatory response promotes an increase in glycolytic activity within neutrophils, leading to an increase in lactate production and release [92]. Lactate produced during neutrophil glycolysis stimulate the expression of pro-inflammatory genes in the early stage of inflammation [93]. However, as lactate accumulates, the process of lactylation triggers M2-like macrophage polarization in a time-dependent manner, referred to as the ‘lactate clock’, thereby regulating the inflammatory response. In the late phase of inflammation, lactylation induces the transformation of M1-like macrophages into M2-like macrophages through epigenetic mechanisms, thus facilitating the repair of tissue damaged caused by inflammation [94].

Succinate has also been shown to exert different immunomodulatory effects in macrophages. During LPS-induced activation, macrophages shift from oxidative phosphorylation to glycolysis, leading to intracellular succinate accumulation that stabilizes HIF-1α and promotes IL-1β production, reinforcing M1 polarization [95]. Conversely, extracellular succinate can signal through the SUCNR1 receptor to favor M2-like polarization, thereby contributing to an immunosuppressive tissue environment [96].

Arginine is a key amino acid for macrophages, and its metabolism determines their function, particularly in the context of macrophage polarization. Upon activation, macrophages use L-arginine through two major competing enzymatic pathways: nitric oxide synthase (iNOS) and arginase. In classically activated M1 macrophages, inducible iNOS converts arginine to nitric oxide (NO) and citrulline, promoting antimicrobial activity and sustaining inflammatory responses [97]. In contrast, alternatively activated M2 macrophages preferentially express arginase-1 (Arg1), which metabolizes arginine into ornithine and urea. Ornithine serves as a precursor for polyamines and proline, facilitating tissue repair, collagen synthesis, and wound healing [97]. Activated neutrophils release Arg1 from cytoplasmic granules, thereby competing with macrophage iNOS for the shared substrate L-arginine [98]. Arg1 was significantly up-regulated in different MI animal models, and arginase activity was demonstrated to be markedly up-regulated as early as 20 min after reperfusion and maintained on day 8 post-MI [99,100]. Increased arginase competes with iNOS for arginine utilization, resulting in decreased NO production and citrulline/ornithine ratio [99,101]. Depletion of local arginine availability suppressed NO production in macrophages, attenuated pro-inflammatory M1 polarization [102], and promoted a shift toward a reparative, M2-like phenotype [103]. Additionally, immature neutrophils, which are released during the inflammatory phase [104] generate increased levels of arginine-derived metabolites like ornithine and spermidine [105]. Ornithine was shown to modulate macrophage function, particularly through the enzyme ornithine decarboxylase, which regulates M1 macrophage activation during infection [106]. In some contexts, ornithine from arginine metabolism is converted into polyamines like putrescine, which is necessary for optimal macrophage responses, such as the internalization of apoptotic cells [107]. Spermidine has been shown to promote an anti-inflammatory M2-like phenotype through mtROS-dependent AMPK activation, Hif-1α stabilization and autophagy induction [108].

All these findings support the concept of a reciprocal metabolic dialog between neutrophils and macrophages. Through their released metabolites and metabolic enzymes, each cell type adjusts the other’s energy metabolism, polarization state, and inflammatory output, thereby influencing the delicate balance between inflammation and repair in cardiovascular injury.

Resident CCR2⁻ and CCR2⁺ cardiac macrophages act as the first sensors of released DAMPs following cardiomyocyte ischemic cell death. Recent studies revealed that these two subsets differentially regulate neutrophil and monocyte recruitment after myocardial injury. CCR2⁺ macrophages were found to be indispensable for neutrophil extravasation into the myocardium in a mouse model of ischemia–reperfusion. In this model, free DNA and histones released by necrotic cardiomyocytes served as activators of CCR2⁺ resident cardiac macrophages via the TLR9/MyD88 signaling axis, prompting them to produce and release CXCL2 and CXCL5. Both proteins serve critical roles in neutrophil recruitment, as the absence of CXCL5 was associated with defects in crawling on the endothelial surface, and CXCL2 interrupts the cascade more upstream, by impairing neutrophil adhesion to the endothelium [5]. Also, in a mouse model of MI, depletion of resident CCR2⁺ macrophages resulted in substantially less monocyte, macrophage, and neutrophil recruitment in the first 2 days following myocardial injury, and reduced interstitial fibrosis after 28 days, suggesting that depletion of CCR2⁺ macrophages alone is enough to limit the initial inflammatory response and subsequent fibrosis. In contrast, a lack of resident cardiac CCR2⁻ macrophages led to shifts in monocyte fate specification, increased macrophage proliferation, increased infarct area, reduced LV systolic function, and exaggerated LV remodeling, highlighting their protective role [4].

Collectively, these findings indicate that resident macrophage subsets not only dictate the recruitment of leukocytes to the myocardium but also determine their fate after infiltration. In addition, it points to CCR2⁺ resident cardiac macrophages as an essential upstream mediator of the inflammatory response to cardiac injury, by regulating the intensity of recruitment in the first wave of both neutrophils and monocytes to the affected tissue. As such, disruption of the balance between CCR2⁻ and CCR2⁺ resident cardiac macrophage subsets can either dampen or exacerbate the inflammatory response to injury, with important effects on subsequent tissue repair dynamics and cardiac function. The aging heart provides an eloquent example of the consequences of such an imbalance. Here, the self-renewal capacity of CCR2-resident embryonic cardiac macrophages declines with age, and they are gradually replaced by CCR2⁺ macrophages derived from circulating monocytes [25,109]. RNAseq analysis revealed that recruited CCR2⁺ macrophages are distinct from tissue-resident CCR2⁺ and CCR2⁻ macrophage subsets, and are a particularly inflammatory population that expresses higher levels of inflammatory chemokines (Cxcl1, Cxcl2, Ccl2, Ccl7, Ccl9), cytokines (IL-1β, IL-10), and genes implicated in adverse cardiac remodeling (Areg, Ereg, Gdf3) [4]. As this inflammatory subset becomes the dominant resident macrophage population, the heart becomes primed to initiate an exacerbated inflammatory response when tissue injury occurs, explaining in part the association with excessive inflammation and worse outcomes after MI [17].

Despite accumulating evidence supporting the role of CCR2⁺ and CCR2⁻ resident macrophages in LV remodeling following MI and of more in-depth characterization of the gene profile of these subsets, the mechanisms involved in their interaction and cross-talk with infiltrating neutrophils and monocyte-derived macrophage subtypes following injury remain unclear.

After MI, neutrophils tend to accumulate in the border zone [110], where they perform key functions to prepare the injured tissue for scar formation and ensure macrophage recruitment and polarization. The sequence of inflammatory and reparative events that is triggered following MI serves to ensure scar formation and preserve adequate heart function. For this purpose, the intensity and temporal organization of these events must be tightly regulated, either through direct cell–cell interactions or paracrine signaling. Because of their central role in the inflammatory phase, increased neutrophil infiltration or delayed neutrophil removal can lead to a prolonged inflammatory response and contribute to post-MI adverse LV remodeling. In contrast, in the absence of robust recruitment of neutrophils, debris is improperly removed, resulting in the accumulation of excess granulation tissue and unstable scar formation. A landmark study by Horckmans et al. showed that neutrophil depletion in mice worsens cardiac function and accelerates progression to heart failure after MI, providing direct evidence that neutrophils are indispensable for effective repair [32]. These mice appeared to “skip” the inflammatory phase and showed reduced expression of M1 markers, together with an increase in resident macrophage proliferation. Also, although M2 markers were upregulated in the heart, MertK expression was decreased, and removal of apoptotic cells was impaired, pointing to neutrophils as critical regulators of the microenvironment that drives macrophage polarization towards M1 and its importance for subsequent tissue repair.

Excessive M1 polarization can amplify the inflammatory phase with deleterious effects on tissue repair. This exacerbated inflammation may be due to HMGB1 and S100A8/A9, which signal through TLR4 and RAGE on monocytes/macrophages and neutrophils, driving their differentiation toward pro-inflammatory phenotypes [17,111]. Elevated circulating levels of these DAMPs have been reported in MI patients and were correlated with adverse clinical outcomes such as heart failure, cardiac rupture, and in-hospital cardiac death [112]. These complications likely arise from excessive immune cell recruitment and their polarization into a pro-inflammatory subtype, leading to exacerbated inflammation and impaired resolution. Another mechanism responsible for defective resolution may be dependent on abundant MMPs released from neutrophil granules. Among these, MMP-9 can activate IL-1β and IL-8 by proteolytic cleavage, generating a positive feedback loop for neutrophil and macrophage activation and chemotaxis [113]. This can also result in prolonged inflammation, and MMP-9 plasma levels were correlated with MI mortality, LV remodeling, and dysfunction in humans [114].

Timely apoptosis of activated neutrophils is known to limit inflammation and promote the transition to the reparatory phase after MI. One of the mechanisms responsible for neutrophil apoptosis and removal in the MI microenvironment is driven by MMP-12, a protein mainly secreted by macrophages. In vivo, MMP-12 inhibition resulted in prolonged pro-inflammatory cytokine upregulation by neutrophils, failed upregulation of TGFβ proteins, hyaluronic acid accumulation, and impaired inflammation resolution after MI. Even though inhibition of MMP-12 did not affect the initial size of the infarct area, it resulted in a greater reduction in ejection fraction because of adverse LV remodeling on day 7 post-MI [115]. Moreover, apoptotic neutrophils can release annexin A1 and lactoferrin, which further inhibit neutrophil recruitment and promote infiltration of anti-inflammatory macrophages [116]. Since MMP-12 is preferentially secreted by M2 macrophages, this further establishes a positive feedback loop that promotes inflammation resolution.

Sex and age are emerging as critical determinants of immune responses following MI, influencing both the magnitude of inflammation and repair. Experimental and clinical data indicate that male and female hearts exhibit distinct inflammatory trajectories post-MI, partly driven by differences in sex hormones and immune cell composition [117,118]. Older MI patients exhibit ~30% higher mortality compared with younger individuals [119], a difference partly attributed to an exaggerated inflammatory response [120] driven by chronic, low-grade sterile inflammation known as inflammaging.

In aged mice, neutrophil production and recruitment to the infarcted myocardium are diminished [121], whereas in humans, the number remains largely unchanged, but their functionality is impaired, showing delayed apoptosis, increased oxidative bursts, and excessive NET formation [122,123]. Similarly, both human and mouse macrophages exhibit a reduction in MHC-II surface expression [124], with mouse macrophages also exhibiting diminished cytokine production and impaired phagocytic activity [125]. Enhanced neutrophil-driven inflammation activates macrophages, whose polarization also becomes dysregulated with aging. Instead of efficiently transitioning from the pro-inflammatory M1 phenotype toward the reparative M2 phenotype after MI, aged macrophages maintain an inflammatory profile, secreting IL-1β, TNF-α, and IL-6. This dysregulation impairs clearance of necrotic tissue, prolongs inflammation, and reinforces neutrophil–macrophage crosstalk, creating a self-sustaining inflammatory loop. Consequently, these processes promote fibrosis and adverse ventricular remodeling, contributing to impaired cardiac repair, functional decline, and residual inflammatory risk [126,127]. In addition, aging profoundly impacts the adaptive immune response, leading to reduced circulating lymphocyte number and the accumulation of functionally impaired memory lymphocytes [128]. All these changes impact neutrophil–macrophage cross-talk and clinically translate into an elevated neutrophil-to-lymphocyte ratio (NLR) in the elderly, a marker currently used as an indicator of systemic inflammation. Elevated NLR has been shown to correlate with organ damage [129] and to predict increased morbidity and mortality following cardiovascular events [130]. In addition, NLR was shown to be a strong predictor of the presence and number of carotid atherosclerotic plaques in older adults, performing better than CRP and fibrinogen [131], and was positively correlated with the Global Registry of Acute Coronary Events (GRACE) score currently used to predict in-hospital mortality of patients with acute MI [132]. Moreover, NLR can enhance the predictive precision of the GRACE score and can be used independently to forecast the risk of major adverse cardiovascular events (MACE) during hospitalization [133].

Regarding sex and age differences, men tend to experience acute MI at younger ages than women, who typically present about 7-10 years later, often post-menopause. Estrogen, mainly as 17β-estradiol (E2), plays a key role in protecting women’s cardiovascular health. After menopause, E2 levels drop sharply to levels similar to men, which is linked to increased cardiovascular risk and faster LV remodeling [134].

After MI, notable sex-based differences emerge in the innate and adaptive responses that influence cardiac repair. While estrogen has direct anti-inflammatory effects on blood vessels, women have a higher baseline immune setpoint, manifesting as more robust macrophage activation, greater antibody generation, with higher lymphocyte counts, lymphocyte to monocyte ratio, and higher adaptive immune response through Th1/Th17 polarization [117,135,136]. Due to stronger adaptive immune activation, women have an earlier reparative response but may also experience prolonged inflammation and consecutive fibrosis following MI [137]. Men, on the other hand, exhibit a more robust and earlier innate immune response, marked by increased neutrophil activation. Studies in murine models have shown that neutrophil counts post-MI were higher in male than female mice, which translates into a larger ischemic area, greater adverse remodeling, and a higher risk of heart failure with reduced ejection fraction [138,139]. Compared to young male mice, female mice have fewer neutrophils in the infarcted myocardium, but are more efficient at clearing debris and exhibit reduced pro-inflammatory gene expression, indicating better resolution of inflammation [138,139]. Estrogen appears to play a role in these differences also by promoting an anti-inflammatory and pro-resolving macrophage phenotype through ERα signaling, helping to limit excessive inflammation and fibrosis [140].

Overall men face a higher absolute risk and tend to experience cardiovascular disease earlier, but women’s relative risk rises significantly after menopause, and they often face worse outcomes once the disease develops.