Ehrlichia chaffeensisdownregulates surface Toll-like receptors 2/4, CD14 and transcription factors PU.1 and inhibits lipopolysaccharide activation of NF-κB, ERK 1/2 and p38 MAPK in host monocytes

Abstract

SummaryMicrobial ligands, such as lipopolysaccharide (LPS), activate Toll-like receptors (TLRs) of mononuclear phagocytes, thus activating transcription factors including NF-k k k k B and inducing antimicrobial activity. Ehrlichia chaffeensis , an obligatory intramonocytic Gram-negative bacterium, causes human monocytic ehrlichiosis. In the present study, we found that E. chaffeensis-infected human monocytes became progressively less responsive to Escherichia coli lipopolysaccharide (LPS) in activating NF-k k k k B and mobilizing ehrlichiacidal activities. E. chaffeensis infection caused downregulation of the expression of several pattern recognition receptors, such as CD14, TLR2 and TLR4, as revealed by flow cytometry and/or reverse transcription polymerase chain reaction analysis. Electrophoretic mobility shift assay revealed that the activity of a transcription factor PU.1 was also downregulated by E. chaffeensis infection. ERK 1/2 and p38 MAPK were slightly activated at the early stage of E. chaffeensis infection; however, the activations of ERK 1/2 and p38 MAPK by LPS treatment were subsequently reduced in E. chaffeensis -infected monocytes compared with those in uninfected monocytes. Like E. chaffeensis , the p38 MAPK-specific inhibitor SB 203580 downregulated PU.1 activity and the expression of TLR2, TLR4 and CD14 in human monocytes, suggesting that the inhibition of p38 MAPK by E. chaffeensis is involved in the suppression of several downstream signalling pathways. These data point to a novel mechanism by which E. chaffeensis can survive by inhibiting critical signalling in monocyte activation pathways linked to pattern recognition receptors.

Functional Genomics of Innate Host Defense Molecules in Normal Human Monocytes in Response toAspergillus fumigatus

“…Down-regulation of the gene encoding CD14, a surface protein expressed on monocytes and macrophages, has been reported previously in human monocytes in response to the obligatory intracellular parasite Ehrlichia chaffeensis (25). E. chaffeensis down-regulated mRNA expression of TLR2, TLR4, and CD14, genes coding for key pattern recognition receptors.…”

Two Monoclonal Antibodies with Defined Epitopes of P44 Major Surface Proteins NeutralizeAnaplasma phagocytophilumby Distinct Mechanisms

“…After 12 h, the medium was replaced with fresh RPMI 1640 medium supplemented with 5% FBS and 2 mM L-glutamine. The host cell-free organisms were then coincubated with HL-60 cells at 37°C for several days to allow the growth of internalized A. phagocytophilum (19). The infection of A. phagocytophilum and Ehrlichia chaffeensis was evaluated by Diff-Quik staining.…”

“…To analyze whether MAb 5C11 and MAb 3E65 block infection of A. phagocytophilum, host cellfree organisms were preincubated with MAbs and then coincubated with HL-60 cells at 37°C for several days to allow the growth of internalized A. phagocytophilum (19). As shown in Fig.…”

Ehrlichia chaffeensis Induces Monocyte Inflammatory Responses through MyD88, ERK, and NF-κB but Not through TRIF, Interleukin-1 Receptor 1 (IL-1R1)/IL-18R1, or Toll-Like Receptors

“…Induction of proinflammatory cytokines in THP-1 cells by E. chaffeensis is dependent on ERK and NF-B pathways. The ability of E. chaffeensis Arkansas to limit MAPK activity has been suggested as an important virulence mechanism (26). Therefore, we examined whether ERK1/2 (p44/p42) is activated by strain Wakulla and whether this is dose dependent.…”