Introduction: Primary aldosteronism (PA), most commonly caused by aldosterone-producing adenomas (APAs), represents the leading form of surgically curable secondary hypertension. While genomic studies have elucidated the mutational landscape of APAs, the spatial organisation and functional role of immune populations across APAs, aldosterone-producing micronodules (APMs), and adjacent adrenal cortex remain poorly defined at single-cell resolution. Methodology: Single-cell RNA sequencing (scRNA-seq) was integrated with spatial transcriptomics in APAs and paired adjacent adrenal cortex, complemented by immunohistochemical (IHC) validation. Immune populations were spatially mapped using canonical markers (CD14, CD68, CD163, HLA-DR, CD8A, and CD4) across defined adrenocortical regions. Results: The adrenal microenvironment in PA demonstrates structured immune organisation rather than passive infiltration. CD14+ monocyte-lineage cells localize intraparenchymally within APAs (n = 10), intercalating between CYP11B2+ aldosterone-producing cells and forming a pattern distinct from perivascular immune niches. scRNA-seq further identified a transcriptionally distinct CD14+ population within the zona reticularis (zR) that co-expresses steroidogenic markers (CYB5A, SULT2A1, TSPAN12) while lacking canonical monocyte transcripts. IHC supported this observation, demonstrating CD14 expression within adrenocortical zR parenchymal cells (n = 5). In parallel, CD4 and HLA-DRA exhibited diffuse cytoplasmic staining within zR parenchymal cells in the absence of classical macrophage marker coexpression (CD68), suggesting non-canonical or context-dependent expression within steroidogenic compartments. CD68+ and CD163+ macrophages were sparsely distributed across APA, APM and adjacent cortex, consistent with lowdensity tissue-resident populations, while CD8A+ cytotoxic lymphocytes were enriched in APAs and APMs with diffuse parenchymal cytoplasmic staining of CD8A additionally observed within the zR. Conclusion These findings reveal a previously unrecognized spatially organised immune-steroidogenic interface within the adrenal cortex. The presence of immune-associated transcriptional and protein signatures within zR cells suggests potential functional plasticity of steroidogenic cells, possibly extending to antigen presentation-related pathways, warranting further mechanistic investigation
Hyperaldosteronism ; Humans

Hypertension is highly prevalent in Malaysia and even the rest of the world. Primary aldosteronism (PA) is one of the most common treatable cause of secondary hypertension. PA occurs due to excessive secretion of aldosterone in the adrenal glands. Up to one in five resistant hypertension cases are due to PA. Therefore, there are a high number of individuals who have the potential to be cured of their hypertension. However, this is difficult to achieve due to limitations in the procedure of diagnosing the PA disease. The challenge now is to know the best usage of available diagnostic methods to detect those who would most likely be cured of hypertension which may be associated with the genotype of the disease. In the past decade, five genes have been found to cause excess aldosterone production in aldosteroneproducing adenomas (APAs), namely KCNJ5, ATP1A1, ATP2B3, CACNA1D and CTNNB1. These somatic mutations have been found to activate the intracellular signaling pathway that regulates aldosterone production. Studies on bilateral adrenal hyperplasia (BAH) samples also have identified the genetic causes for the many hereditary hyperaldosteronism, namely familial hyperaldosteronism types I, II, III, and IV/V. Herein we review the genetic factors of PA as a result of either aldosterone-stimulating somatic mutations or germline variants, and the associated clinical phenotype.