Cross-Talk between HLA Class I and TLR4 Mediates P-Selectin Surface Expression and Monocyte Capture to Human...

Area of Science:

• Immunology
• Transplantation Immunology
• Cellular Signaling

Background:

• Donor-specific HLA antibodies (HLA Abs) drive antibody-mediated rejection (AMR) by activating endothelial cells (ECs) and recruiting leukocytes.
• The precise molecular mechanisms of HLA Ab-mediated EC activation and leukocyte recruitment are not fully understood.

Purpose of the Study:

• To investigate whether Toll-like receptors (TLRs) function as coreceptors for human leukocyte antigen class I (HLA I) in ECs.
• To elucidate the role of TLR4 in HLA I-mediated endothelial cell activation and monocyte recruitment.

Main Methods:

• Screening of TLR expression on human aortic ECs.
• Coimmunoprecipitation assays to detect complex formation between HLA I and TLR4.
• Small interfering RNA (siRNA) knockdown of TLR4 and MyD88 to assess functional impact.
• Measurement of P-selectin expression, von Willebrand factor release, and monocyte recruitment.

Main Results:

• Human aortic ECs express TLR3, TLR4, TLR6, and TLR10; only TLR4 is found on the EC surface.
• HLA Ab stimulation increases complex formation between HLA I and TLR4 on ECs.
• Knockdown of TLR4 or MyD88 inhibits HLA I Ab-induced P-selectin expression, von Willebrand factor release, and monocyte recruitment.

Conclusions:

• TLR4 serves as a novel coreceptor for HLA I in stimulating monocyte recruitment on activated ECs.
• HLA I molecules form distinct signaling complexes with TLR4 (for monocyte capture) and integrin β4 (for firm adhesion), both contributing to AMR.