654 - Myeloid-KLF2 knockout neonatal mice experience mortality from lipopolysaccharide in an age-dependent and cell-specific manner

Preterm neonates experience increased mortality from Gram negative sepsis as compared to term neonates. The innate immune system is at a critical phase of development during the neonatal period. Mechanisms underlying activation of the preterm neonatal innate immune response are poorly understood. Our prior data has shown that Kruppel-like factor (KLF)-2 is a critical transcription factor necessary to maintain murine myeloid cells in a quiescent state (Mahabeleshwar G, Immunity 2011).

Objective: We hypothesized that myeloid KLF2 plays a critical role in the murine neonatal immune response in Gram negative sepsis and that loss of KLF2 from myeloid cells leads to increased mortality (decreased survival) in an age dependent and cell specific manner in neonatal mice.

Design/Methods:

Preterm neonatal (postnatal day (P) 4) and term neonatal (P12) myeloid KLF2 knockout (MyK2KO) and age matched myeloid Cre mice were given 5ug/gm of E. coli O55:B5 lipopolysaccharide (LPS) toxin via intraperitoneal (i.p.) injection. For in vivo cell depletion studies, antibodies were injected i.p. 24 hours prior to LPS injection, followed by a repeat dose 24h after LPS. Ly6G antibody was used for neutrophil depletion, CD115 for monocyte depletion and equal dose of both for depletion of both cell lines.

Results:

P4 MyK2KO mice have significantly decreased survival within 48 hours of LPS exposure as compared to P4 myeloid Cre mice (19% vs 59%, n=19, p< 0.01, Χ² test, Figure 1). At P12, there is 100% survival of both groups of mice. In vivo depletion of either neutrophils, monocytes or both together increased survival in P4 MyK2KO mice from 19% to 37%, 47%, and 45% respectively (Figure 2).

Conclusion(s):

Preterm neonatal mice lacking myeloid KLF2 have decreased survival after exposure to LPS endotoxin as compared to term neonatal MyK2KO or age-matched control mice. In vivo depletion of neutrophils, monocytes, or both prior to LPS increases survival in MyK2KO mice exposed to LPS. Future studies will focus on the mechanism underlying this postnatal age-specific and cell-specific role of myeloid-KLF2 in the neonatal innate immune response.