SERPINB1 as a critical regulator of inflammation and protease activity in human monocytic cells.

SERPINB1, a member of the serpin superfamily, functions primarily as a serine protease suicide inhibitor via its reactive center loop (RCL). While murine studies have elucidated its role in neutrophil homeostasis and survival, the functions and pathways orchestrated by human SERPINB1, particularly in monocytes, remain largely undefined. Here, we demonstrate that SERPINB1 is under purifying selection, indicative of an essential, non-redundant role in human immunity comparable to that of genes known to cause immune diseases when mutated. Flow cytometric and Western blot analyses reveal ubiquitous expression in immune cells, with monocytes exhibiting the highest levels and the most active utilization of SERPINB1. Using CRISPR/Cas9-mediated knockout in THP-1 monocytic cells, we found that SERPINB1 deficiency does not impair cell viability but significantly enhances proinflammatory responses, notably increasing IL-1β production in response to lipopolysaccharide stimulation. Bulk RNA sequencing corroborated upregulation of inflammatory genes, while activity-based proteomic profiling uncovered broad alterations in enzymatic activity, affecting pathways beyond protease regulation, including ribosomal function and cellular metabolism. These findings suggest that human SERPINB1 extends its function beyond protease inhibition to modulate monocyte inflammatory activation and metabolic processes. Further mechanistic investigations are warranted to delineate the molecular interactions underpinning SERPINB1's regulatory network in monocytes. Yet, our study provides novel insights into SERPINB1's multifaceted functions in human immunity and highlights its potential as a therapeutic target for controlling dysregulated inflammation.