NK cell hyperactivation drives macrophage repolarization and limits M2 bias in pemphigus vulgaris

Macrophages and natural killer (NK) cells are innate immune components proven to be either pathogenic, protective, or both in autoimmune disorders. Nonetheless, the function of macrophages in the pathogenesis of pemphigus vulgaris (PV), an autoimmune skin disorder, is lacking.

We aimed to investigate macrophages and their crosstalk with NK cells in PV, with a particular focus on how these interactions influence their functionalities.

Flow cytometry and immunofluorescence was utilised to assess macrophage profile along with expression of receptors on NK cells and macrophages. In-vitro macrophage skewing, and NK-macrophage interactions (including F-actin accumulation, activation markers, cytotoxicity, IFNγ and perforin secretion, NOS2, CD86, CD206 expression, phagocytic activity, and arginase activity were examined. NKG2D blocking and related assays were performed to elucidate its role in crosstalk.

Expression of NKG2D on NK cells and MICA/B on macrophages was upregulated. CD56⁺ NK cells and CD68⁺ macrophages co-localized in lesions. A significant increase in macrophages in both the periphery and lesional skin was observed. Both M1 and M2 macrophages were upregulated in blood, whereas M1 increased and M2 decreased in skin lesions. Macrophages displayed skewing toward an M2 phenotype in vitro. Upon co-culturing, F-actin accumulation increased during interaction. The interaction led to increased activation, cytotoxicity, and IFNγ and perforin secretion in NK cells when M1 stimulation and Dsg3 autoantigen were given. In macrophages, increased expression of iNOS and CD86 and higher phagocytic activity were noted, whereas arginase activity and expression along with CD206 were downregulated. NKG2D blockade on NK cells resulted in partial but significant decrease in NK cells activity including activation, perforin, cytotoxicity and IFNγ release. The reduction were prominent in M1 state. M1 like markers NOS2 and CD86 were reduced and arginase activity non significantly improved under M2 state post blockade.

This study helped in comprehending functionally active NK- macrophage axis, where NK cells promote pro inflammatory M1 state, and dysregulate M2 macrophage functionality. NKG2D blockade resulted in partial reversal suggesting its critical, though not elusive, contribution indicating multifactorial crosstalk mechanism. Targeting NK cell activity or promoting M2 functionality could potentially lead to improvements in disease pathogenesis.