Impact of pleural anthracosis severity on the structure and function of subcarinal lymph nodes

Introduction

Pleural anthracosis (PA), characterized by the deposition of carbonaceous particles on the pleural surface, is a common pathological finding, particularly in populations with significant exposure to air pollution or biomass smoke (1). While historically considered a benign marker of environmental exposure, emerging evidence suggests that PA may have significant pathological consequences beyond mere discoloration. Notably, studies have linked PA to pleural effusion, with proposed mechanisms involving the obstruction of parietal pleural lymphatic channels by anthracotic nodules, thereby inhibiting fluid reabsorption (2). Additionally, PA has been linked to both structural and functional changes within the pleural lymphatic system. Studies show that severe anthracosis is associated with pleural thickening, a reduced prevalence of long, straight-running lymphatic vessels, and compromised pleural lymphatic drainage, as observed through near-infrared fluorescence imaging (3). These lymphatic changes are not merely anatomical curiosities; they have been shown to influence the metastatic behavior of lung cancer, interfering with nodal skip metastasis patterns (3). This evolving understanding positions PA not as an inert bystander but as an active modifier of local pleural and lymphatic microenvironment.

The lymph nodes (LNs), particularly the mediastinal station such as the subcarinal node, serve as a critical hub for immune surveillance and a potential gateway for metastatic spread in thoracic malignancies (4). While inhaled particulate matter within the central airways conventionally traverses the intrapulmonary and hilar lymphatic chain (N1), the visceral pleura possesses a distinct, superficial lymphatic network with unique drainage kinetics. Comprehensive anatomical mapping has demonstrated that approximately 20% to 25% of subpleural lymphatic vessels drain directly into the mediastinal LNs, completely bypassing the N1 hilar stations. The subcarinal LNs serve as a major anatomical convergence point for this direct pleuro-mediastinal drainage, particularly receiving subpleural lymphatics from the lower lobes, the middle lobe, and the lingula via the inferior pulmonary ligaments (5). Consequently, in the setting of PA, where the carbonaceous particulate burden is heavily concentrated at the visceral pleural surface, subcarinal LNs, constitute a primary and direct downstream target for the sequestration of pleural particulates, making them an ideal anatomical site for evaluating regional immune tissue remodeling. Its structure, comprising a capsule, cortex, and medulla with specialized sinus systems, is finely tuned to filter lymph and coordinate immune responses. The functional integrity of LNs is paramount, with their cellular composition, proliferative activity, vascularity, and macrophage content reflecting local and systemic immune status. In the context of environmental exposures, LNs are primary sites for the sequestration of particulate matter, including carbon particles. For instance, anthracosis has been documented in thoracic LNs, and its presence has been linked to the accumulation of radionuclides like Polonium-210, suggesting a role as a reservoir for airborne pollutants (6). However, the existing literature has predominantly focused on the parenchymal aspects of anthracosis or its association with specific clinical syndromes like anthracofibrosis (7). A significant gap remains in systematically elucidating how the burden of pleural carbon deposition—a direct indicator of environmental particle load—translates to structural and functional remodeling within the downstream draining LNs, such as the subcarinal LNs.

The primary objective of this study is to investigate the impact of varying degrees of PA on the structural and functional integrity of subcarinal LNs. By systematically analyzing a spectrum of histological and immunohistochemical parameters, we aim to determine whether a higher burden of pleural carbon deposition is associated with specific patterns of LNs remodeling, such as increased fibrosis, altered proliferative index, or changes in vascular and immune cell profiles. This research seeks to bridge the gap between environmental pleural pathology and regional lymphatic node biology, providing novel insights into how chronic particulate exposure may precondition the lymphatic microenvironment, with potential implications for understanding cancer biology and immune function in polluted environments. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-1274/rc).

Methods

Patients

This study recruited all patients undergoing pulmonary surgery at the Department of Thoracic Surgery of Shandong Cancer Hospital and Institute between August 7, 2025 and November 28, 2025. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Shandong Cancer Hospital and Institute (No. SDTHEC2024003152). The samples we used were all the remaining samples necessary for completing clinical testing, and the requirement for informed consent from the patients was waived for this retrospective study.

The following criteria were used for patient selection.

Inclusion criteria required participants to: be at least 18 years old; have received no prior lung cancer treatment; have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1; present with computed tomography (CT)-confirmed ground-glass pulmonary nodules (axial diameter ≤20 mm, solid component <5 mm); and undergo video-assisted thoracoscopic surgery (VATS).

Exclusion criteria comprised: a history of malignancy within the past 5 years; prior local radiotherapy or systemic antitumor therapy; unstable systemic disease; current or prior interstitial lung disease; pleural adhesions; pulmonary infections; or thoracotomy.

LNs collection

LN specimens were obtained from patients presenting with pulmonary nodules who were scheduled for surgery and satisfied predetermined eligibility criteria (these patients underwent mediastinal LNs dissection and the LNs were pathologically confirmed to be negative).

PA assessments

Based on our literature (8) and our clinical experience, we classified PA into four degrees: 0= no PA (Figure 1A), 1= dotted PA (Figure 1B), 2= linear or blocky PA (Figure 1C), and 3= patchy PA (Figure 1D) (due to our limited data, it is possible to make a one-to-one comparison, and the PA grading among the three doctors is consistent).

Figure 1 Photos of different levels of PA captured during thoracoscopic surgery. (A) No pleural anthracosis; (B) dotted pleural anthracosis; (C) linear or blocky pleural anthracosis; (D) patchy pleural anthracosis. PA, pleural anthracosis.

In addition to grading data, we incorporated measurement data into the analysis. The ratio of the PA area within the images was determined using the ImageJ software (https://imagej.nih.gov/ij/docs/intro.html). Specifically, the outline of the black region (PA area) was extracted and delineated, and the PA ratio was computed as follows: PA ratio = PA area/pleural area (Figure 2A-2C) (8).

Figure 2 How to calculate the PA ratio using ImageJ. (A) PA ratio = PA area/pleural area; (B) circle the PA area through ImageJ (within the range of the yellow curve); (C) PA ratio = proportion of black area. PA, pleural anthracosis.

Histopathological evaluation

Hematoxylin-eosin (HE) staining assessments

Preparation of pathological sections

Tissue specimens were fixed in 4% paraformaldehyde. After fixation, they were processed in strict accordance with the Standard Operation Procedure (SOP) for trimming, dehydration, embedding, sectioning, staining, and mounting. Once these steps were completed, the samples were deemed suitable for microscopic evaluation.

Image acquisition and analysis instrument

Images were captured using a PANNORAMIC DESK/MIDI/250/1000 system (3DHISTECH, Hungary), and the browsing software utilized for viewing is CaseViewer version 2.4 (3DHISTECH, Hungary).

Immunohistochemistry assessments

The corresponding subcarinal LNs were then subjected to a detailed histopathological and immunohistochemical panel. Beyond standard HE staining for general architecture and pigment localization, we employed Masson’s trichrome and Elastica van Gieson (EVG) stains to assess collagen and elastic fiber deposition, respectively. Furthermore, we utilized immunohistochemistry for Ki-67 (a proliferation marker), CD31 (an endothelial marker for vasculature), CD68 (a macrophage marker), and D2-40 (a lymphatic endothelial marker) to quantitatively evaluate LN function across dimensions of cellular proliferation, vascularity, immune cell infiltration, and lymphangiogenesis.

Statistical analysis

Categorical variables were reported as percentages and assessed using the chi-square test or Fisher’s exact test, as appropriate. Continuous variables were summarized as mean ± standard deviation (SD) and compared via analysis of variance (ANOVA). Linear regression was employed to examine relationships between numerical variables, and Pearson’s correlation coefficient was used to evaluate their associations. All tests were two-sided, and a P value <0.05 was considered statistically significant. Data were analyzed using SPSS version 24.0 (SPSS, Inc., Chicago, IL, USA).

Given the large number of correlated quantitative immunohistochemical endpoints evaluated [including positive cell ratio, density, mean optical density, H-score, and Immunoreactive Score (IRS) across four distinct markers], this study was prospectively designed to be exploratory and hypothesis-generating in nature. Consequently, formal statistical adjustments for multiple comparisons (e.g., Bonferroni corrections) were not applied to the primary P values, as these endpoints represent highly inter-dependent measures of the same biological phenomena. The significance levels reported should therefore be interpreted within an exploratory context.

Results

Clinical characteristics

We conducted a prospective evaluation of 79 subjects from August 7, 2025 to November 28, 2025. Table 1 summarize the clinical and characteristics of patients according to different PA levels. Compared to smoking history (P=0.25), age has a significant impact on PA (P<0.01). As the level of PA increases, although there are no significant differences in various indicators of lung function, they all show a downward trend.

Pathological characteristics (Figures 3-7)

Figure 3 Comprehensive histopathological and immunohistochemical characterization of lymph node tissue at PA level 1. (A) Images corresponding to PA ratio =2% and PA level =1. (B,C) The lymph node tissue corresponding to (A) has a thin layer of capsule on its surface; the parenchyma is divided into two parts: cortex and medulla, with a clear boundary (HE staining). Multiple black deposits (yellow arrows) can be seen in both the medulla and cortex. The black box indicates the location of the magnified view. (D,E) Under Masson staining, the collagen fibers in the lymph node tissue corresponding to (A) are stained blue. A small amount of collagen fibers can be seen on the capsule of the lymph node tissue, and no significant abnormalities in collagen fiber content are observed. The black box indicates the position of the magnified view. (F,G) In the EVG staining of the lymph node tissue corresponding to (A), the elastic fibers are stained black, and no obvious elastic fibers are observed in the lymph node tissue. The black box indicates the location of the magnified view. (H-K) Immunohistochemical staining of lymph node tissue for CD31 (H), CD68 (I), D2-40 (J), and Ki67 (K), with corresponding positive cell counting. EVG, Elastica van Gieson; HE, hematoxylin-eosin; PA, pleural anthracosis.

Figure 4 Comprehensive histopathological and immunohistochemical characterization of lymph node tissue at PA level 2. (A) Images corresponding to PA ratio =20% and PA level =2. (B,C) The lymph node tissue corresponding to (A) has a thin layer of capsule on its surface; the parenchyma is divided into two parts: cortex and medulla, with a clear boundary (HE staining). The cortex is rich in lymphocytes; a large amount of black substance deposition can be seen in the medulla (yellow arrows). The black box indicates the position of the magnified view. (D,E) Under Masson staining, the collagen fibers in the lymph node tissue corresponding to (A) are stained blue. A small amount of collagen fibers can be seen on the capsule of the lymph node tissue, and no significant abnormalities in collagen fiber content are observed. The black box indicates the position of the magnified view. (F,G) In the EVG staining of the lymph node tissue corresponding to (A), the elastic fibers are stained black, and no obvious elastic fibers are observed in the lymph node tissue. The black box indicates the position of the magnified view. (H-K) Immunohistochemical staining of lymph node tissue for CD31 (H), CD68 (I), D2-40 (J), and Ki67 (K), with corresponding positive cell counting. EVG, Elastica van Gieson; HE, hematoxylin-eosin; PA, pleural anthracosis.

Figure 5 Comprehensive histopathological and immunohistochemical characterization of lymph node tissue at PA level 3. (A) Images corresponding to PA ratio =90% and PA level =3. (B,C) The lymph node tissue corresponding to (A) has a thin layer of capsule on its surface; large areas of black substance deposition (yellow arrows) are visible in both the cortex and medulla (HE staining). The black box indicates the location of the magnified view. (D,E) Under Masson staining, the collagen fibers in the lymph node tissue corresponding to (A) are stained blue, and a small amount of collagen fiber proliferation can be seen locally in the lymph node tissue (yellow arrows). The black box indicates the position of the magnified view. (F,G) In the EVG staining of the lymph node tissue corresponding to (A), elastic fibers are stained black, and a small amount of elastic fibers can be seen locally in the lymph node tissue (yellow arrows). The black box indicates the position of the magnified view. (H-K) Immunohistochemical staining of lymph node tissue for CD31 (H), CD68 (I), D2-40 (J), and Ki67 (K), with corresponding positive cell counting. EVG, Elastica van Gieson; HE, hematoxylin-eosin; PA, pleural anthracosis.

Figure 6 Positive cells of different ratio of PA. PA, pleural anthracosis.

Figure 7 Comprehensive histopathological and immunohistochemical characterization of lymph node tissue at PA level 0. (A) Images corresponding to PA ratio =0 and PA level =0. (B,C) The lymph node tissue corresponding to (A) has a thin layer of capsule on its surface; large areas of black substance deposition (yellow arrows) are visible in both the cortex and medulla (HE staining). The black box indicates the location of the magnified view. (D,E) Under Masson staining, the collagen fibers in the lymph node tissue corresponding to (A) are stained blue, and a small amount of collagen fiber proliferation can be seen locally in the lymph node tissue. The black box indicates the position of the magnified view. (F,G) In the EVG staining of the lymph node tissue corresponding to (A), the elastic fibers are stained black, and no obvious elastic fibers are observed in the lymph node tissue. The black box indicates the position of the magnified view. (H-K) Immunohistochemical staining of lymph node tissue for CD31 (H), CD68 (I), D2-40 (J), and Ki67 (K), with corresponding positive cell counting. EVG, Elastica van Gieson; HE, hematoxylin-eosin; PA, pleural anthracosis.

Comparison of HE staining of LNs corresponding to different degrees of PA: the surface of LNs tissue has a thin layer of capsule; the parenchyma is divided into cortex and medulla, with a clear boundary, and the cortex is rich in lymphocytes; a large amount of black material deposition can be seen in the capsule and medulla. As the proportion of deposition increases, the deposition of black material in the LNs also increases (Figures 3B,3C,4B,4C,5B,5C,7B,7C).

Masson staining of LNs corresponding to different degrees of subpleural carbonaceous particulate matter deposition: under Masson staining, collagen fibers are stained blue, and a small amount of collagen fiber proliferation can be seen locally in the LNs tissue, with no significant differences in collagen fiber proliferation among the groups. (Figure 3D,3E,4D,4E,5D,5E,7D,7E).

EVG staining of LNs corresponding to different degrees of subpleural carbonaceous particulate matter deposition: elastic fibers are stained black, and no significant elastic fibers are observed in the LNs tissues of all groups. Only a small amount of elastic fibers can be seen in the LNs of the group with 90% deposition (Figure 3F,3G,4F,4G,5F,5G,7F,7G).

Ki67, CD31, CD68, and D2-40 calculation of LNs corresponding to different degrees of subpleural carbonaceous particulate matter deposition: as the proportion of deposition increases, the positive cell ratio, positive cell density, mean density, H-score, and IRS show a trend of first increasing and then decreasing (Figure 3H-3K,4H-4K,5H-5K,7H-7K) The ratio of PA at 20% is the turning point (Figure 6).

Discussion

Anthracosis, a condition characterized by the deposition of carbonaceous particles within lung tissues and pleura, is increasingly recognized not merely as an inert marker of environmental exposure but as a potential modifier of pulmonary pathophysiology (9). Given the significant baseline association between advancing age and increasing PA severity, patient age was identified a priori as a critical potential confounder. This is due to the well-established effects of immunosenescence, which intrinsically drives age-related structural disorganization, decreased vascularity, and altered cellularity within human LNs. While traditionally associated with parenchymal changes and bronchial obstruction, emerging evidence highlights its significant impact on pleural and lymphatic structures (3). This is particularly relevant in the context of lung cancer, where the interplay between environmental lung disease, lymphatic drainage, and tumor biology can influence disease progression and treatment outcomes (10). Our study focuses on a specific aspect of this interaction: the structural and functional alterations in the subcarinal LNs associated with varying degrees of PA in early-stage lung cancer patients, aiming to elucidate how carbon burden may precondition the regional lymphatic microenvironment.

The most striking finding of this study is the biphasic response of the cellular markers Ki67, CD31, CD68, and D2-40, which uniformly peaked at a PA ratio of approximately 20% (through visual examination of the scatter plot, a clear biphasic distribution was observed, leading to the identification of a 20% threshold for the PA ratio) before experiencing a precipitous decline. While the current study design did not incorporate direct molecular assays for cellular apoptosis or immune exhaustion, this non-linear dynamic aligns closely with established toxicological models of carbon nanoparticle exposure. Experimental models consistently demonstrate that low-dose exposure to carbon black nanoparticles induces a robust, acute inflammatory response characterized by rapid macrophage polarization, cellular proliferation, and compensatory angiogenesis. However, as the particulate burden escalates and exceeds the phagocytic clearance threshold, carbon nanoparticles induce severe cytotoxicity (11). Mechanistically, carbon particles accumulate within macrophage lysosomes, leading to physical lysosomal swelling and membrane disruption—a process described as nanomechanical buckling. This lysosomal damage precipitates the release of cathepsin B and the activation of the NLRP3 inflammasome, a cascade that ultimately triggers inflammatory cell death via caspase-1 dependent pyroptosis and caspase-3 mediated apoptosis (12). Therefore, the sharp decline in cellular markers observed at higher PA grades in our cohort likely reflects a state of physical cellular overload and nanoparticle-induced cytotoxicity, rather than classical, receptor-mediated immune checkpoint exhaustion. Future investigations incorporating specific molecular markers for apoptosis (e.g., cleaved caspase-3) and pyroptosis (e.g., gasdermin D) are essential to definitively validate this mechanical toxicity hypothesis within the human lymphatic microenvironment.

This investigation systematically evaluated subcarinal LNs from patients without nodal metastasis, stratified by PA severity quantified via thoracoscopic imaging. We employed a comprehensive histological and immunohistochemical panel—including HE, Masson, EVG, Ki67, CD31, CD68, and D2-40 staining—to assess architectural changes, fibrosis, cellular proliferation, angiogenesis, macrophage infiltration, and lymphatic endothelial integrity (13-15). Preliminary findings indicate a direct correlation between PA grade and nodal carbon deposition, alongside a non-linear, biphasic response in proliferative, vascular, and immune markers. The following discussion interprets these results in the context of existing literature on anthracosis-induced lymphatic remodeling (8) and considers the potential implications for lymphatic function and immune surveillance in the pre-metastatic niche.

The present study provides novel insights into the structural and functional alterations of subcarinal LNs in response to varying degrees of PA, a condition characterized by the deposition of carbonaceous particles on the pleural surface. While the association between PA and pleural lymphatic dysfunction has been documented, with studies showing that severe anthracosis leads to pathological changes in pleural lymphatics and decreased drainage, thereby interfering with nodal skip metastasis in lung cancer, the direct impact of PA on the architecture and cellular function of regional LNs, particularly the subcarinal nodes, remains largely unexplored. The observed microenvironmental changes within the nodes—such as altered macrophage density and dynamic vascularity—represent an independent, concurrent pathophysiological process occurring within the highly cellular lymphoid tissue itself, driven by physical particulate accumulation, which is distinct from the upstream mechanical blockade of pleural lymphatic fluid drainage. Our findings demonstrate a dose-dependent accumulation of black particulate matter within the LNs capsule and medulla, correlating with the macroscopic blackening of the lung. This observation aligns with the known pathophysiology of anthracosis as a marker of environmental particulate exposure (6). Contrary to the dense fibrotic scarring and architectural distortion classically observed in clinical anthracofibrosis syndromes, our histological evaluation utilizing Masson’s trichrome and EVG stains revealed minimal to absent collagen and elastic fiber deposition across the vast majority of PA grades. Overt extracellular matrix remodeling was sparsely observed, and only at the extreme upper limit of carbon deposition (90% PA grade). These findings indicate that in patient populations with subclinical or incidental environmental particulate exposure, PA induces dynamic cellular shifts within the LN—specifically involving macrophage populations, lymphatic endothelium, and vascular networks—rather than driving classical fibrotic or desmoplastic remodeling. The micro-architectural disruption observed is primarily one of cellular displacement, resulting from the accumulation of carbon-laden macrophages within the medullary and cortical sinuses, rather than collagenous tissue replacement. This pattern, characterized by an initial increase followed by a decline in markers for proliferation (Ki67), angiogenesis (CD31), macrophage infiltration (CD68), and lymphatic endothelium (D2-40), suggests that PA induces a state of chronic, subclinical immune activation that may eventually lead to functional exhaustion or remodeling of the nodal microenvironment. This biphasic response has not been previously reported in the context of anthracosis and represents a significant contribution to understanding how chronic environmental insult shapes the immune landscape of regional lymphoid tissue.

The clinical implications of these findings are potentially significant for the management of lung cancer patients, who frequently present with varying degrees of PA. The altered LNs microenvironment we describe could influence the nodal immune response to tumor antigens and affect the patterns of lymphatic metastasis. For instance, the initial increase in lymphatic markers (D2-40) and macrophage activity might temporarily enhance antigen surveillance, whereas the subsequent decline could impair immune trafficking and contribute to the “altered lymphatic structure and function” previously linked to atypical metastatic patterns (3). Furthermore, the accumulation of carbon-laden macrophages within nodes may physically obstruct lymphatic sinuses or alter cytokine milieus, potentially explaining the association between anthracosis and transudative pleural effusions due to blocked lymphatic reabsorption (9). From a therapeutic standpoint, understanding that PA is associated with a quantifiable, dynamic change in the LNs immune milieu is crucial. In the era of immunotherapy, the functional status of regional LNs is a key determinant of treatment response (16). LNs microenvironment primed by chronic particulate exposure might respond differently to immune checkpoint inhibitors. Although evidence is scarce, case reports suggest that careful management of concurrent mycobacterial infection is possible during immunotherapy for lung cancer (10), highlighting the need for a nuanced approach in patients with complex pulmonary comorbidities like PA. Our data suggest that the degree of PA could serve as a histological biomarker for predicting the immune competency of regional LNs, which may inform decisions regarding the extent of LNs dissection or the use of neoadjuvant therapies.

The clinical and biological implications of this biphasic shift in the nodal microenvironment remain an important area for future investigation. The dynamic fluctuation in macrophage density (CD68) and lymphatic endothelial integrity (D2-40) unequivocally demonstrates that regional LNs in patients with moderate to severe PA possess an altered baseline cellular architecture. While it is theoretically plausible that the physical displacement of nodal architecture by carbon-laden macrophages, or the induction of localized nanoparticle cytotoxicity, could alter local antigen presentation dynamics, the present study evaluated exclusively pathologically negative LNs. Consequently, direct conclusions regarding how PA influences metastatic efficiency, overall patient survival, or responsiveness to systemic therapies cannot be drawn from these data. The current findings strictly establish that PA acts as an independent modifier of local node cellularity and vascularity. This underscores the critical need for longitudinal, matched-cohort studies to determine whether this baseline environmental remodeling intersects meaningfully with tumor immunology or clinical oncological outcomes.

Despite these insights, our study has several limitations that must be acknowledged. First, the sample consisted exclusively of subcarinal LNs from early-stage lung cancer patients without nodal metastasis. While this design allowed us to isolate the effects of PA from those of overt malignancy, it limits the generalizability of our findings to healthy individuals or to LNs involved by metastatic disease. The observed biphasic trends in cellular markers require validation in a larger, independent cohort to confirm the inflection points and their clinical correlates. Second, the absence of comprehensive epidemiological data regarding the patients’ lifelong occupational histories, residential proximity to urban air pollution, or historical exposure to biomass smoke and dust. In the context of the present study, the thoracoscopically quantified PA ratio serves as an objective, internal proxy dosimeter for total particulate burden, thereby mitigating the reliance on potentially flawed or incomplete retrospective self-reporting of environmental exposures. Third, our study is cross-sectional, capturing a snapshot of LNs status at a single time point. Longitudinal studies tracking LNs changes in relation to the progression of PA or the development of lung cancer would be invaluable to establish causality and understand the temporal dynamics of the biphasic response. Future research should also incorporate molecular profiling to elucidate the signaling pathways driving the observed cellular changes and investigate whether similar alterations occur in other thoracic LN stations (17,18). Fourth, the present study design is the exclusive focus on subcarinal LNs without a parallel, comparative analysis of intrapulmonary or hilar (N1) LNs. Although compelling anatomical evidence supports the existence of direct pleuro-mediastinal drainage pathways to station 7, particularly from the lower lung fields, an integrated analysis evaluating the entire N1-to-N2 lymphatic axis would provide a more comprehensive understanding of the topographical gradient of carbon deposition. Future investigations incorporating paired analyses of sequential lymphatic stations are warranted to fully map the multi-level microenvironmental impact of PA.

Conclusions

This study systematically reveals for the first time the dynamic correlation between the degree of PA and the structural and functional markers of subcarinal LNs. Although the collagen and elastic fiber components of the LNs did not significantly change with carbon deposition, key indicators reflecting cell proliferation (Ki67), angiogenesis (CD31), macrophage infiltration (CD68), and lymphatic vessel distribution (D2-40) all exhibited a nonlinear trend of initial increase followed by decrease. This suggests that a certain degree of PA may initially activate the immune and clearance responses of the LNs, while excessive deposition may lead to functional inhibition or exhaustion. These findings provide a new pathological perspective for understanding the long-term effects of environmental particulate matter exposure on regional immune hubs, and suggest that PA should be considered as a potential influencing factor when assessing the immune status of lung cancer patients or high-risk populations.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-1274/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-1274/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-1274/prf

Funding: This study was supported by Taishan Scholar Project Special Fund (No. tsqn202312367) and Shandong Provincial Natural Science Foundation Youth General Project (No. ZR2024QH455).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-1274/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Shandong Cancer Hospital and Institute (No. SDTHEC2024003152). The samples we used were all the remaining samples necessary for completing clinical testing, and the requirement for informed consent from the patients was waived for this retrospective study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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