CD14, a GPI-linked protein, plays a pivotal role in LPS-mediated signaling by potentiating leukocyte adherence, activation, and cytokine production. Recent studies have identified the Toll-like receptor 4 (TLR4) as a membrane cofactor in LPS-mediated transmembrane signaling in cytokine induction, although the mechanism responsible for this cooperation is unknown. Using fluorescence resonance energy transfer (RET) techniques, we demonstrate that LPS triggers a physical association between CD14 and TLR4. Because LPS stimulation up-regulates CD14 and TLR4 expression, it was necessary to control for the possibility that these newly expressed molecules were associated with one another independent of LPS stimulation. Although the calcium ionophore A23187 increased the expression of CD14 and TLR4, they did not exhibit energy transfer. However, following A23187 treatment, LPS promoted physical proximity between CD14 and TLR4. Therefore, we suggest that a close interaction between CD14 and TLR4 participates in LPS signaling, leading to nuclear translocation of NF-κB.

Fever is a phylogenetically ancient response that is associated with improved survival in acute infections. In endothermic animals, fever is induced by a set of pyrogenic cytokines [tumor necrosis factor-α (TNF-α), interleukin (IL)-1, and IL-6] that are also essential for survival in acute infections. We studied the influence of core temperature on cytokine expression using an anesthetized mouse model in which core temperature was adjusted by immersion in water baths. We showed that raising core temperature from basal (36.5–37.5°C) to febrile (39.5–40°C) levels increased peak plasma TNF-α and IL-6 levels by 4.1- and 2.7-fold, respectively, and changed the kinetics of IL-1β expression in response to lipopolysaccharide challenge. TNF-α levels were increased predominantly in liver, IL-1β levels were higher in lung, and IL-6 levels were widely increased in multiple organs in the warmer mice. This demonstrates that the thermal component of fever may directly contribute to shaping the host response by regulating the timing, magnitude, and tissue distribution of cytokine generation during the acute-phase response.

Fever improves survival in acute infections, but the effects of increased core temperature on host defenses are poorly understood. Tumor necrosis factor alpha (TNF-␣) is an early activator of host defenses and a major endogenous pyrogen. TNF-␣ expression is essential for survival in bacterial infections but, if disregulated, can cause tissue injury. In this study, we show that passively increasing core temperature in mice from the basal (36.5 to 37.5°C) to the febrile (39.5 to 40°C) range modifies systemic TNF-␣ expression in response to bacterial endotoxin (lipopolysaccharide). The early TNF-␣ secretion rate is enhanced, but the duration of maximal TNF-␣ production is shortened. We identified Kupffer cells as the predominant source of the excess TNF-␣ production in the warmer animals. The enhanced early TNF-␣ production observed at the higher temperature in vivo could not be demonstrated in isolated Kupffer cells or in precision-cut liver slices in vitro, indicating the participation of indirect pathways. Therefore, expression of the endogenous pyrogen TNF-␣ is regulated by increments in core temperature during fever, generating an enhanced early, self-limited TNF-␣ pulse.

Fever improves survival in acute infections, but the effects of increased core temperature on host defenses are poorly understood. Tumor necrosis factor alpha (TNF-α) is an early activator of host defenses and a major endogenous pyrogen. TNF-α expression is essential for survival in bacterial infections but, if disregulated, can cause tissue injury. In this study, we show that passively increasing core temperature in mice from the basal (36.5 to 37.5°C) to the febrile (39.5 to 40°C) range modifies systemic TNF-α expression in response to bacterial endotoxin (lipopolysaccharide). The early TNF-α secretion rate is enhanced, but the duration of maximal TNF-α production is shortened. We identified Kupffer cells as the predominant source of the excess TNF-α production in the warmer animals. The enhanced early TNF-α production observed at the higher temperature in vivo could not be demonstrated in isolated Kupffer cells or in precision-cut liver slices in vitro, indicating the participation of indirect pathways. Therefore, expression of the endogenous pyrogen TNF-α is regulated by increments in core temperature during fever, generating an enhanced early, self-limited TNF-α pulse.

Purpose: Osteoarthritis involving the ankles has been relatively understudied. We have previously demonstrated associations of older age, obesity, and prior injury with prevalent radiographic ankle OA (rAOA) in a community-based cohort (Lateef 2017), but little is known Abstracts / Osteoarthritis and Cartilage 28 (2020) S86eS527 S402