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Introduction: Endometriosis is a chronic, estrogen-dependent inflammatory disorder affecting approximately 10% of women of reproductive age. Retrograde menstruation is widely accepted as a primary mechanism for ectopic endometrial seeding; however, only a subset of individuals develop the disease. This suggests additional pathogenic processes. Increasing evidence suggests impaired immune surveillance as a central factor enabling ectopic endometrial tissue to persist and expand. This review aims to explore immune-associated pathogenic mechanisms in endometriosis, focusing on the interplay between natural killer (NK) cells, cytokines, and extracellular vesicles (EVs).

Methods: This study was conducted as a narrative review. Relevant PubMed studies addressing immune dysfunction in endometriosis were identified, with emphasis on the role of NK cells, cytokines, EVs, and EV-mediated signaling. All material chosen for referral in the review consists of published reports that were critically evaluated and discussed.

Results: Endometriosis is associated with impaired immune surveillance, characterized by reduced NK-cell cytotoxicity, driven by altered receptor expression and a shift toward regulatory NK-cell subsets. A dysregulated cytokine milieu combines pro-inflammatory signals that promote lesion growth with immunosuppressive factors that inhibit immune clearance of ectopic tissue. Lesion-derived EVs further contribute the lesions' survival by suppressing cytotoxic immune function, inducing apoptosis of activated immune cells and promoting inflammation and angiogenesis. The referred results highlight key immunological mechanisms underlying endometriosis.

Discussion: This review presents an immune-based model in which NK-cell dysfunction, cytokine imbalance, and EV-mediated signaling cooperate to establish an immune-privileged microenvironment that promotes the survival and growth of ectopic endometrial tissue. The immune escape mechanism, described here, highlights potential targets as candidates to be tested for immunomodulatory therapies. We conclude that endometriosis should be considered a disorder fundamentally linked to mechanisms of immune dysregulation.