Jessica dos Santos and Leo Joosten, theme Infectious diseases and global health, and colleagues, describe in Cell Reports that trained immunity induced by b-glucan confers protection against L. braziliensis infections. Infection control is associated with IL-32 and IL-1 induction. Genetic variation in the IL-32 gene enhances induction of trained immunity leading to proinﬂammatory gene transcription in bone marrow hematopoietic stem and progenitor cells.
American tegumentary leishmaniasis is a vector-borne parasitic disease caused by Leishmania protozoans. Innate immune cells undergo long-term functional reprogramming in response to infection or Bacillus Calmette-Guerin (BCG) vaccination via a process called trained immunity, conferring non-speciﬁc protection from secondary infections. They demonstrate that monocytes trained with the fungal cell wall component b-glucan confer enhanced protection against infections caused by Leishmania braziliensis through the enhanced production of proinﬂammatory cytokines. Mechanistically, this augmented immunological response is dependent on increased expression of interleukin 32 (IL-32). Studies performed using a humanized IL-32 transgenic mouse highlight the clinical implica-tions of these ﬁndings in vivo. This study represents a deﬁnitive characterization of the role of IL-32g in the trained phenotype induced by b-glucan or BCG, the results of which improve the understanding of the molecular mechanisms governing trained immunity and Leishmania infection control.