Membrane CD14, but not soluble CD14, is used by exoenzyme S fromP. aeruginosato signal proinflammatory cytokine production

Abstract

Recognition of TLR agonists involves a complex interplay among a variety of serum and cell membrane molecules, including mCD14 and sCD14 that is not fully understood. TLR activation results in downstream signaling that induces inflammatory cytokine production in response to pathogenic molecules, such as ExoS, which is a TLR2 and TLR4 agonist produced by the opportunistic pathogen Pseudomonas aeruginosa. We reasoned that responses to ExoS, a protein, might differ from canonical TLR agonists such as LPS. Stimulating the expression of mCD14 with vitamin D3 enhanced the response to ExoS and LPS. Also, blocking anti-CD14 antibody or removing mCD14 using PLC reduced responses to ExoS and LPS. Furthermore, CD14-deficient cells were unable to bind and respond to ExoS, which was restored by stable transfection of mCD14, indicating that mCD14 was required for the response to ExoS. However, addition of sCD14 to culture enhanced responsiveness to LPS but not ExoS. Moreover, the addition of serum did not alter the response to ExoS but enhanced the response to LPS. Despite differences of adaptor molecule use between ExoS and LPS, lipid antagonists that compete for LPS binding to CD14 also inhibited the response to ExoS. These results highlight a fundamental difference between TLR agonists in their requirements for CD14 and serum components. These results suggest that understanding the dissimilarities and targeting overlapping sites of interaction on CD14 may yield a synergistic, clinical benefit during infections where a variety of TLR agonists are present.

Absence of c-Maf and IL-10 enables Type I IFN enhancement of innate responses to low-dose LPS in alveolar macrophages

“…For example, CD14 has been shown to be required for sensing of Mtb component trehalose 6,6’-dimycolate (TDM) along with TLR2 and MARCO 40 , and other TLR2 associated mycobacterial lipoproteins 41 . CD14 is also known to contribute to the recognition of necrotic cells 42 , several different types of LPS from gram-negative bacteria 43 , flagellin 44 , and Legionella pneumophila 45 . Further investigation into how CD14 expression levels impact AM-specific pathogen sensing will shed light on whether CD14 expression is significantly impacting the early pulmonary response to other respiratory pathogens.…”

Activation of α7 Nicotinic Acetylcholine Receptor Upregulates HLA-DR and Macrophage Receptors: Potential Role in Adaptive Immunity and in Preventing Immunosuppression

“…The CD14 membrane protein, together with TLR4 and the MD2 adapter molecules, serves as the receptor for such components of gram-negative bacteria as LPS [49]. Binding of LPS to CD14 leads to the activation of immune cells and excessive production of TNF-α, playing a critical role in sepsis [50]. Systemic inhibition of CD14 reduces inflammation in sepsis [51].…”