NLRP3 inflammasome signaling orchestrates hepatic granuloma organization and protective immunity

In a study of experimental visceral leishmaniasis, researchers have uncovered a crucial role for the NLRP3 inflammasome in the organization of protective hepatic granulomas. This immune structure defends the host against persistent pathogens. The researchers analyzed samples from patients with active disease and found elevated levels of inflammasome-associated mediators, which correlated with systemic inflammation.

In mice, Leishmania infantum infection triggered NLRP3 inflammasome activation within hepatic granulomas. Single-cell and spatial transcriptomic analyses revealed high levels of inflammasome-associated transcription in hepatic macrophages and regions associated with granulomas. However, the NLRP3 deficiency did not prevent the initial formation of granulomas, but it did impair their expansion, cellular organization, and the accumulation of leukocytes.

For this response to occur, the researchers found that NLRP3 required the presence of Caspase-1/11 and IL-18, but it was independent of IL-1β. Interestingly, the loss of NLRP3 also led to impaired parasite control despite reducing hepatic inflammation and histopathological alterations. Overall, these findings highlight NLRP3-Caspase-1/11-IL-18 signaling as a vital mechanism for coordinating the cellular and spatial organization of protective hepatic granulomas.

This discovery demonstrates that granuloma architecture plays a previously unrecognized role in inflammasome-mediated immunity, providing valuable insight into host resistance in visceral leishmaniasis, a potentially fatal neglected tropical disease.