Protection against lethal sepsis following immunization with species varies by isolate and inversely correlates with bone marrow tissue damage.

Protection against lethal ()/ () intra-abdominal infection (IAI)-mediated sepsis can be achieved by a novel form of trained innate immunity (TII) involving Gr-1+ myeloid-derived suppressor cells (MDSCs) that are induced by inoculation (immunization) with low virulence species [i.e., ()] that infiltrate the bone marrow (BM). In contrast, more virulent species (i.e., ), even at sub-lethal inocula, fail to induce similar levels of protection. The purpose of the present study was to test the hypothesis that the level of TII-mediated protection induced by strains inversely correlates with damage in the BM as a reflection of virulence. Mice were immunized by intraperitoneal inoculation with several parental and mutant strains of deficient in virulence factors (hyphal formation and candidalysin production), followed by an intraperitoneal challenge 14 d later and monitored for sepsis and mortality. Whole femur bones were collected 24 h and 13 d after immunization and assessed for BM tissue/cellular damage via ferroptosis and histology. While immunization with standard but not sub-lethal inocula of most wild-type strains resulted in considerable mortality, protection against lethal / IAI challenge varied by strain was usually less than that for , with no differences observed between parental and corresponding mutants. Finally, levels of protection afforded by the strains were inversely correlated with BM tissue damage ( = -0.773). TII-mediated protection against lethal sepsis induced by strain immunization inversely correlates with BM tissue/cellular damage as a reflection of localized virulence.