Lethality in LPS-induced endotoxemia in C3H/HeCr mice is associated with prevalence of proinflammatory cytokines: lack of protective action of lactoferrin

C3H/HeCr mice are more susceptible to infection compared with other strains. Lactoferrin (LF), a protein involved in innate defense, was shown to protect mice against lethal endotoxemia. In this investigation we attempt to explain the cause of increased susceptibility of C3H/HeCr mice to LPS and lack of protective LF action in these mice. We found that C3H/HeCr mice produced up to 5-fold more serum TNFalpha and 66% higher IFNgamma levels in response to i.v. LPS injection than the control, CBA strain. 24 h pretreatment of C3H/HeCr mice with LF did not cause inhibition of the LPS-induced TNFalpha serum levels, whereas in CBA mice LF significantly decreased TNFalpha level. IL-6 serum levels, in turn, were lowered in C3H/HeCr mice but elevated in CBA mice. That differential regulation of cytokine production by LF in C3H/HeCr mice paralleled a decreased survival after lethal LPS injection - 10% vs. 60% in control, PBS treated mice. In addition, determination of colony forming units (CFU) in livers and spleens after administration of 10(8) Escherichia coli revealed that pretreatment of CBA mice with LF caused a marked reduction of CFU in these organs, whereas in C3H/HeCr mice the changes were insignificant. These results indicate that the altered TNFalpha/IL-6 ratio in C3H/HeCr mice, as compared to control CBA mice, as well as the increased IFNgamma level, may be responsible for the increased susceptibility to endotoxemia in that substrain. We also suggest that an association exists between the LF protective effect against endotoxic sequelae and the insult-induced systemic immune response.